Primary hyperparathyroidism: review and recommendations on evaluation, diagnosis, and management. A Canadian and international consensus.

The purpose of this review is to assess the most recent evidence in the management of primary hyperparathyroidism (PHPT) and provide updated recommendations for its evaluation, diagnosis and treatment. A Medline search of "Hyperparathyroidism. Primary" was conducted and the literature with the highest levels of evidence were reviewed and used to formulate recommendations. PHPT is a common endocrine disorder usually discovered by routine biochemical screening. PHPT is defined as hypercalcemia with increased or inappropriately normal plasma parathyroid hormone (PTH). It is most commonly seen after the age of 50 years, with women predominating by three to fourfold. In countries with routine multichannel screening, PHPT is identified earlier and may be asymptomatic. Where biochemical testing is not routine, PHPT is more likely to present with skeletal complications, or nephrolithiasis. Parathyroidectomy (PTx) is indicated for those with symptomatic disease. For asymptomatic patients, recent guidelines have recommended criteria for surgery, however PTx can also be considered in those who do not meet criteria, and prefer surgery. Non-surgical therapies are available when surgery is not appropriate. This review presents the current state of the art in the diagnosis and management of PHPT and updates the Canadian Position paper on PHPT. An overview of the impact of PHPT on the skeleton and other target organs is presented with international consensus. Differences in the international presentation of this condition are also summarized.

Diagnosis of asymptomatic primary hyperparathyroidism: proceedings of the third international workshop.

OBJECTIVE: Asymptomatic primary hyperparathyroidism (PHPT) is a common clinical problem. The purpose of this report is to guide the use of diagnostic tests for this condition in clinical practice. PARTICIPANTS: Interested professional societies selected a representative for the consensus committee and provided funding for a one-day meeting. A subgroup of this committee set the program and developed key questions for review. Consensus was established at a closed meeting that followed. The conclusions were then circulated to the participating professional societies. EVIDENCE: Each question was addressed by a relevant literature search (on PubMed), and the data were presented for discussion at the group meeting. CONSENSUS PROCESS: Consensus was achieved by a group meeting. Statements were prepared by all authors, with comments relating to accuracy from the diagnosis subgroup and by representatives from the participating professional societies. CONCLUSIONS: We conclude that: 1) reference ranges should be established for serum PTH in vitamin D-replete healthy individuals; 2) second- and third-generation PTH assays are both helpful in the diagnosis of PHPT; 3) DNA sequence testing can be useful in familial hyperparathyroidism or hypercalcemia; 4) normocalcemic PHPT is a variant of the more common presentation of PHPT with hypercalcemia; 5) serum 25-hydroxyvitamin D levels should be measured and, if vitamin D insufficiency is present, it should be treated as part of any management course; and 6) the estimated glomerular filtration rate should be used to determine the level of kidney function in PHPT: an estimated glomerular filtration rate of less than 60 ml/min.1.73 m2 should be a benchmark for decisions about surgery in established asymptomatic PHPT.

Effects of hepatectomy, nephrectomy, and nephrectomy/uremia on the metabolism of parathyroid hormone in the rat.

Reports from several laboratories, showing extensive hepatic extraction of circulating parathyroid hormone, led us to examine the effect of near-total hepatectomy on the metabolism of the hormone to circulating fragments, and on its clearance from plasma. The rate of disappearance of (125)I-labeled and unlabeled bovine parathyroid hormone from plasma, and the appearance, disappearance, and chemical and immunochemical characteristics of circulating fragments were examined by gel filtration and either sequence-specific radioimmunoassays or sequence analysis using the Edman reaction. Results from awake rats subjected to near-total hepatectomy were compared with those found in sham-treated, nephrectomized, and short-term uremic rats (studied 2 d after nephrectomy). When compared with the sham-treated group, all other groups clear (125)I-labeled hormone more slowly; after hepatectomy, however, the clearance rate is most strikingly decreased. After injection of intact hormone, the concentration of carboxy-terminal fragments in the circulation of hepatectomized rats is greatly reduced at all time intervals when compared with that in sham-treated rats. Sequence analysis of plasma samples, collected from rats into which (125)I-labeled hormone had been injected, shows that carboxy-terminal fragments having positions 34 and 37 of the intact hormone sequence as their amino-terminal amino acids are abundant in sham-treated, nephrectomized, and nephrectomized/uremic rats, but are undetectable in hepatectomized rats. The data suggest that inasmuch as the liver in vivo generates most of the carboxy-terminal fragments resulting from the metabolism of injected hormone, specific cell types within the liver must be the principal locus of the responsible enzyme(s); thus, studies of the enzymic properties of isolated hepatic cells in vitro most likely will yield information of physiologic relevance to the metabolism of the hormone in the intact animal.

Analysis of parathyroid hormone and its fragments in rat tissues: chemical identification and microscopical localization.

After intravenous injection of [(125)I]-iodo-parathyroid hormone in the rat, uptake of the hormone was greatest in the liver and kidneys. Uptake was rapid, reaching a maximal concentration by 4 and 8 min, respectively. Extracts, prepared from both these organs at intervals soon after the injection of intact hormone, showed three main radioactive peaks when samples were subjected to gel filtration under protein-denaturing conditions. The first peak coeluted with intact hormone. The second eluted at a position corresponding to the carboxy-terminal fragments previously described in plasma, and the last eluted at the salt volume of the column. Microsequence analysis of the radioiodinated fragments, a method that has proved valuable for chemically defining the circulating fragments resulting from metabolism of injected hormone, showed that extracts of liver and kidney, prepared at 4 and 8 min after injection of the intact hormone, contained different fragments. The radioiodinated fragments in liver extracts were identical to those previously reported in the plasma of rats and dogs, fragments resulting principally from proteolysis between positions 33 and 34, and 36 and 37 of the intact hormone. Although the same fragments were also present in the kidneys, they constituted less than 15% of the amount present in the liver. More than 50% of the labeled renal fragments consisted of a peptide whose amino-terminal amino acid was position 39 of the intact hormone, a fragment not present in plasma. The rate of appearance of radioiodinated fragments that were chemically identical to those in plasma was more rapid in the liver than in plasma. Correlation of these chemical analyses with studies of the localization of (125)I by autoradiography showed that at the times when the intact hormone and the carboxy-terminal fragments comprised nearly all of the (125)I-labeled moieties in the tissues, the proximal convoluted tubules of the kidney and sinusoidal lining cells of the liver, which probably are Kupffer cells, contained the highest concentration of (125)I. Preferential localization of immunoreactive parathyroid hormone to these tissue sites also was shown by immunoperoxidase staining in studies with unlabeled hormone. Our results suggest that, unless multiple renal mechanisms are present for release of hormonal fragments, one of which releases the circulating fragments preferentially, the liver, rather than the kidney, is principally responsible for generating the carboxy-terminal fragments in plasma after injection of intact hormone, and the Kupffer cells may contain the enzymes that hydrolyze parathyroid hormone.

Circulating PTH molecular forms: what we know and what we don't.

Circulating parathyroid hormone (PTH) molecular forms have been identified by three generations of PTH assays after gel chromatography or high-performance liquid chromatography fractionation of serum. Carboxyl-terminal (C) fragments missing the amino-terminal (N) structure of PTH(1-84) were identified first. They represent 80% of circulating PTH in normal individuals and up to 95% in renal failure patients. They are regulated by calcium (Ca) slightly differently than PTH(1-84), occurring in a relatively smaller proportion relative to the latter in hypocalcemia but in a much larger proportion in hypercalcemia. Synthetic C-PTH fragments do not bind to the PTH/PTHrP type I receptor and are not implicated in the classical biological effect of PTH(1-84). They bind to a different C-PTH receptor and exert biological actions on bone that are opposite to those of PTH(1-84). The integrity of the distal C-structure appears to be important for these biological effects, and it is uncertain if all C-PTH fragments are intact up to position 84. A second category of C-PTH fragment has a partially preserved N-structure. They are called non-(1-84) PTH or N-truncated fragments. They react in Intact (I)-PTH assays but not in PTH assays with a 1-4 epitope. They are acutely regulated by Ca(2+) concentration. They also exert similar hypocalcemic and antiresorptive effects but have 10-fold greater affinity for the C-PTH receptor compared to other C-PTH fragments. Even if they represent only 10% of all C-PTH fragments, they could be as relevant biologically. An N form of PTH other than PTH(1-84) has been identified in the circulation. It reacts very well in PTH assays with a 1-4 epitope but poorly in I-PTH assay with a 12-18 epitope. It is oversecreted in severe primary and secondary hyperparathyroidism and in parathyroid cancers. Its biological activity is still unknown. Overall, these studies suggest that PTH(1-84) and C-PTH fragments are regulated differently to exert opposite biological effects on bone via two different receptors. This may serve to control bone turnover and Ca concentration more efficiently.

Chronic adaptation of dog parathyroid function to a low-calcium-high-sodium-vitamin D-deficient diet.

The development of secondary hyperparathyroidism was studied in relation to changes in serum ionized Ca (Ca2+), 25-OHD, and 1,25-(OH)2D concentrations in six dogs maintained on a low-Ca (0.05%), high-Na (1.6%), and vitamin D-deficient diet for 91 weeks. Blood samples and evaluations of the parathyroid function were obtained before and after 3, 12, 24, 36, and 91 weeks of diet. Serum iPTH was measured by an intact hormone (I) and a carboxy-terminal (C) assay. The sigmoidal relationship between ionized Ca and iPTH values was evaluated mathematically. Results are means +/- SD. Statistically significant changes over a time period were evaluated by an ANOVA for repeated measurements. Over the first 3 weeks, serum Ca2+, 25-OHD, and 1,25-(OH)2D did not change but stimulated I-iPTH increased 84.3 +/- 39.9% (p less than 0.005) and C-iPTH only 25.3 +/- 12.2% (p less than 0.01), a significant difference (p less than 0.02). The increase in stimulated I-iPTH reached 487.4 +/- 139.6% (p less than 0.0001) and 418.4 +/- 76.9% (p less than 0.0001) for C-iPTH by the end of the study. Similar significant increases were seen in basal and nonsuppressible iPTH at or after week 12.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of involution of hyperplastic parathyroid glands in dogs: adaptation via a decrease in the calcium stimulation set point and a change in secretion profile.

This study analyzes the parathyroid function in four dogs before and after 2 years of a low-calcium, high-sodium, vitamin D-deficient diet and the involution of the same function following (1) correction of dietary calcium deficiency and administration of i.v. 1,25-(OH)2D (0.25 micrograms twice per day) during 1 month, (2) after an additional month of normal dog chow supplemented with oral vitamin D (25 micrograms per day), and, finally, (3) after 5 and 17 months of a diet with normal levels of calcium and vitamin D. The parathyroid function was evaluated through i.v. infusion of CaCl2 and Na2 EDTA with measurement of intact (I) and carboxyl-terminal (C) immunoreactive parathyroid hormone (iPTH). The C-iPTH/I-iPTH ratio was calculated to assess the modulation of molecular forms of iPTH induced by the various treatments. The 2 years of calcium and vitamin D deprivation lowered ionized calcium (1.23 +/- 0.04, p < 0.05) and 25-OHD (4.02 +/- 2.06 nM, p < 0.005) and tended to decrease 1,25-(OH)2D (80.8 +/- 8.6 pM); it increased basal I- and C-iPTH levels approximately eightfold (I-iPTH, 40.2 +/- 20.7, p < 0.05; C-iPTH, 185.4 +/- 94.9, p < 0.05) and stimulated I-iPTH (60.2 +/- 23.0 pM, p < 0.05) and C-iPTH (239.6 +/- 80.7 pM, p < 0.05) fivefold. A greater rise in nonsuppressible I-iPTH levels than in C-iPTH levels led to a decreased C-iPTH/I-iPTH ratio in hypercalcemia (12.5 +/- 2.8 versus 27.8 +/- 6.05 pM, p < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of Ca2+ concentration on the clearance and circulating levels of intact and carboxy-terminal iPTH in pentobarbital-anesthetized dogs.

The role of hormone secretion and hormone clearance in the differential control of circulating levels of intact (I-) and carboxy-terminal (C-) immunoreactive parathyroid hormone (iPTH) was evaluated in 18 pentobarbital-anesthetized dogs. Catheters were installed in the aorta, left renal, and hepatic veins for sampling. Hepatic and renal blood flows were calculated from sulfobromophtalein (BSP) and p-aminohippuric acid (PAH) extraction and clearance. I- and C-iPTH were measured during a 1 h of infusion of CaCl2 or Na2EDTA. High-performance liquid chromatography (HPLC) profiles of I- and C-iPTH in and out of the liver and kidney were also obtained. Data on two dogs (one CaCl2 and one Na2EDTA infusion) were pooled for the analysis of one parathyroid function using a four-parameter mathematical model. Results obtained in the basal state and during analysis of the parathyroid function were also compared with those of 24 awakened dogs. Results are means +/- SD. Anesthetized dogs had lower levels of Ca2+ (1.29 +/- 0.03 vs. 1.34 +/- 0.04 mmol/l; p < 0.001) and higher levels of I- (11.5 +/- 5.7 vs. 3.0 +/- 1.9 pmol/l, p < 0.001) and C-iPTH (52 +/- 20.9 vs. 22.8 +/- 10.5 pmol/l; p < 0.001) than awakened dogs. Their stimulated (S) and nonsuppressible (NS) I-iPTH levels were increased 2- and 4-fold, respectively, while similar C-iPTH levels rose only 1.35- and 1.75-fold; this caused their S (4.4 +/- 0.7 vs. 6.8 +/- 1.9; p < 0.001) and NS (24.6 +/- 11.8 vs. 49.8 +/- 27.5; p < 0.05) C-iPTH/I-iPTH ratios to decrease. This was not explained by different renal clearance rates of I- and C-iPTH since both were similar at approximately 10 ml/kg/minute and unaffected by Ca2+ concentration. Clearance of all I- and C-iPTH HPLC molecular forms by the kidney appeared equal. A 50% decrease in the hepatic clearance of I-iPTH to approximately 12 ml/kg/minute in pentobarbital-anesthetized dogs, related to a lower hepatic blood flow, explained the higher levels of S and NS I-iPTH in these animals. I-iPTH hepatic clearance was unaffected by Ca2+ concentration. C-iPTH hepatic clearance was much lower at approximately 5 ml/kg/minute, abolished by hypercalcemia, and reduced by the influence of anesthesia on hepatic blood flow. This also explained the higher S C-iPTH levels in anesthetized animals. I-PTH(1-84) detected by the C-iPTH assay explained only 37.6% of the hepatic C-iPTH clearance in hypocalcemia and 73.3% in hypercalcemia. Overall, our results indicate that total C-iPTH clearance is about 40.2% that of I-iPTH in hypocalcemia and 41.3% in hypercalcemia. This would only explain a 2.4- to 2.5-fold difference in circulating levels of I- and C-iPTH if secretion rates were equal; the larger difference observed in S and NS C-iPTH/I-iPTH ratio values is thus mainly explained by different production rates.

Development of a novel immunoradiometric assay exclusively for biologically active whole parathyroid hormone 1-84: implications for improvement of accurate assessment of parathyroid function.

We developed a novel immunoradiometric assay (IRMA; whole parathyroid hormone [PTH] IRMA) for PTH, which specifically measures biologically active whole PTH(1-84). The assay is based on a solid phase coated with anti-PTH(39-84) antibody, a tracer of 125I-labeled antibody with a unique specificity to the first N-terminal amino acid of PTH(1-84), and calibrators of diluted synthetic PTH(1-84). In contrast to the Nichols intact PTH IRMA, this new assay does not detect PTH(7-84) fragments and only detects one immunoreactive peak in chromatographically fractionated patient samples. The assay was shown to have an analytical sensitivity of 1.0 pg/ml with a linear measurement range up to 2,300 pg/ml. With this assay, we further identified that the previously described non-(1-84)PTH fragments are aminoterminally truncated with similar hydrophobicity as PTH(7-84), and these PTH fragments are present not only in patients with secondary hyperparathyroidism (2 degrees -HPT) of uremia, but also in patients with primary hyperparathyroidism (1 degrees -HPT) and normal persons. The plasma normal range of the whole PTH(1-84) was 7-36 pg/ml (mean +/- SD: 22.7 +/- 7.2 pg/ml, n = 135), whereas over 93.9% (155/165) of patients with 1 degrees -HPT had whole PTH(1-84) values above the normal cut-off. The percentage of biologically active whole PTH(1-84) (pB%) in the pool of total immunoreactive "intact" PTH is higher in the normal population (median: 67.3%; SD: 15.8%; n = 56) than in uremic patients (median:53.8%; SD: 15.5%; n = 318; p < 0.001), although the whole PTH(1-84) values from uremic patients displayed a more significant heterogeneous distribution when compared with that of 1 degrees -HPT patients and normals. Moreover, the pB% displayed a nearly Gaussian distribution pattern from 20% to over 90% in patients with either 1 degrees-HPT or uremia. The specificity of this newly developed whole PTH(1-84) IRMA is the assurance, for the first time, of being able to measure only the biologically active whole PTH(1-84) without cross-reaction to the high concentrations of the aminoterminally truncated PTH fragments found in both normal subjects and patients. Because of the significant variations of pB% in patients, it is necessary to use the whole PTH assay to determine biologically active PTH levels clinically and, thus, to avoid overestimating the concentration of the true biologically active hormone. This new assay could provide a more meaningful standardization of future PTH measurements with improved accuracy in the clinical assessment of parathyroid function.

Metabolism of radioiodinated carboxy-terminal fragments of bovine parathyroid hormone in normal and anephric rats.

[125I]Carboxy-terminal fragments were produced by incubating [125I]bovine PTH(1-84) with plasma membranes from the rat renal cortex. After purification by gel chromatography and characterization by sequence analysis, these fragments, mainly [125I]bovine PTH(41-84), were injected into normal and acutely nephrectomized rats during two different experiments. In each case, blood was obtained from five rats at various time points (2, 4, 6, 8, 12, 24, 48, and 96 min); tissue was taken after they had been killed (4, 8, 24, and 96 min). Plasma and weighted aliquots of tissues were counted. Plasma at each time point and the extract of various tissues at the 8-min mark were further analyzed by gel chromatography. Each radioactivity peak on each profile was identified and quantitated planimetrically. [125I]Carboxy-terminal fragments were extracted from serum biexponentially: the first exponential had a half-life of 2.3 min and the second 27.2 min in normal rats. These values increased to 3.2 min (X 1.4) and 74.0 min (X 2.7) in nephrectomized rats. In normal rats, 125I-extraction was 33.4% (kidney), 15.9% (muscle), 6.9% (bone), less than 2.7% (liver), and under 1% in other tissues. In nephrectomized rats, these values were significantly (P less than 0.005) increased to 24.6% (muscle), 10% (bone), and 6.8% (liver) with less than 1% in other tissues. Most of the 125I-radioactivity present in these tissues at the 8-min time point migrated in the same manner as injected fragments or smaller degradation products generated in situ. Tissues which play a secondary role in circulating carboxy-terminal fragment extraction in normal rats can therefore increase this activity in anephric animals. Extraction overall remains less efficient, as demonstrated by the longer half-life of fragments in nephrectomized rats.

Effects of passive immunization against parathyroid hormone (PTH)-like peptide and PTH in hypercalcemic tumor-bearing rats and normocalcemic controls.

Passive immunization using antisera raised against rat PTH-like peptide [PLP-(1-34)] and rat PTH-(1-84) was used to assess and compare the roles played by PLP and PTH in modulating mineral metabolism in hypercalcemic rats bearing the Rice-500 Leydig cell tumor and in normocalcemic control animals. After immunization, plasma calcium in the tumor-bearing animals rapidly normalized and remained within the normal range for several days, plasma phosphate rose, and urinary phosphate and cAMP fell. These changes were associated with increased longevity of the tumor-bearing rats. Reduction of plasma calcium was shown to be a function of early (5 h) neutralization of PLP bioactivity in the kidney, whereas the effect of immunoneutralization of PLP in bone appeared later (24-48 h) and was more prolonged. Immunization against PTH in normocalcemic animals resulted in a hypocalcemic episode of smaller magnitude and shorter duration than that achieved in hypercalcemic animals immunized against PLP and appeared to be unassociated with neutralization of distal tubular effects. Neutralization of proximal tubular and skeletal actions of PTH appeared to occur in a manner analogous to that seen for PLP in tumor-bearing animals, but were of shorter duration. These studies suggest that in normal animals the action of PTH in the skeleton and/or on vitamin D metabolism contributes considerably more than renal transport activity to the maintenance of normocalcemia and that compensatory mechanisms rapidly restore homeostasis. PTH appears to be the major modulator of calcium homeostasis in normal rats, with PLP playing a minor role, if any. In tumor-bearing rats, mechanisms to restore calcium levels to baseline are delayed after PLP immunoneutralization, and PLP appears to be both necessary and sufficient for the hypercalcemic state.

Metabolism of radioiodinated bovine parathyroid hormone in the rat.

Metabolism of bovine 125I-labeled parathyroid hormone was studied in the rat by gel filtration and by sequence analysis of the iodinated fragments. Analysis of the kinetics of hormone metabolism shows that iodinated intact hormone has a multiexponential disappearance curve with a rapid (3 min) initial and a slower (48 min) second component. Iodinated fragments, which rapidly increase during the first 12 min after injection of the intact hormone, subsequently disappear from the circulation with a t1/2 of no greater than 48 min. Plasma samples collected at various time-intervals after intravenous injection of bovine 125I-labeled parathyroid hormone were gel filtered on Bio-gel P-100. Four radioactive peaks were seen. The first and second peaks eluted, respectively, at the void volume of the column and at the position of intact hormone. The third peak consisted of iodinated fragments, and the last peak eluted at the salt volume of the column. Sequence analysis of the iodinated fragments in the third peak showed that it was heterogeneous, containing several different, but closely related, polypeptides. Before 48 min after injection, the most-abundant fragment is one whose amino-terminal amino acid is residue 34. The amino-terminal residue of the next most-common fragment is the amino acid at position 37. No fragments representing cleavages closer to the amino-terminus than residue 34 were seen. The results of these studies are virtually identical with those previously obtained in the dog. The similarities found in the sites of hormone proteolysis and in the kinetics of hormone metabolism in the rat and dog, coupled with the less direct evidence indicating that similar cleavages are also present in man and bovine, are consistent with the view that proteolysis of parathyroid hormone is peripheral tissues is specific, at least in mammalian species, and may be a critical step in controlling the availability of biologically active hormone.

Synthetic carboxyl-terminal fragments of parathyroid hormone (PTH) decrease ionized calcium concentration in rats by acting on a receptor different from the PTH/PTH-related peptide receptor.

Even if the carboxyl-terminal (C-) fragments/intact (I-) PTH ratio is tightly regulated by the ionized calcium (Ca(2+)) concentration in humans and animals, in health and in disease, the physiological roles of C-PTH fragments and of the C-PTH receptor remain elusive. To explore these issues, we studied the influence of synthetic C-PTH peptides of various lengths on Ca(2+) concentration and on the calcemic response to human (h) PTH-(1-34) and hPTH-(1-84) in anesthetized thyroparathyroidectomized (TPTX) rats. We also looked at the capacity of these PTH preparations to react with the PTH/PTHrP receptor and with a receptor for the carboxyl (C)-terminal portion of PTH (C-PTH receptor) in rat osteosarcoma cells, ROS 17/2.8. The Ca(2+) concentration was reduced by 0.19 +/- 0.03 mmol/liter over 2 h in all TPTX groups. Infusion of solvent over 2 more h had no further effect on the Ca(2+) concentration (-0.01 +/- 0.01 mmol/liter), whereas infusion of hPTH-(7-84) or a fragment mixture [10% hPTH-(7-84) and 45% each of hPTH-(39-84) and hPTH-(53-84)] 10 nmol/h further decreased the Ca(2+) concentration by 0.18 +/- 0.02 (P<0.001) and 0.07+/-0.04 mmol/liter (P< 0.001), respectively. Infusion of hPTH-(1-84) or hPTH-(1-34) (1 nmol/h) increased the Ca(2+) concentration by 0.16 +/- 0.03 (P < 0.001) and 0.19 +/- 0.03 mmol/liter (P < 0.001), respectively. Adding hPTH-(7-84) (10 nmol/h) to these preparations prevented the calcemic response and maintained Ca(2+) concentrations equal to or below levels observed in TPTX animals infused with solvent alone. Adding the fragment mixture (10 nmol/h) to hPTH-(1-84) did not prevent a normal calcemic response, but partially blocked the response to hPTH-(1-34), and more than 3 nmol/h hPTH-(7-84) prevented it. Both hPTH-(1-84) and hPTH-(1-34) stimulated cAMP production in ROS 17/2.8 clonal cells, whereas hPTH-(7-84) was ineffective in this respect. Both hPTH-(1-84) and hPTH-(1-34) displaced (125)I-[Nle(8,18),Tyr(34)]hPTH-(1-34) amide from the PTH/PTHrP receptor, whereas hPTH-(7-84) had no such influence. Both hPTH-(1-84) and hPTH-(7-84) displaced (125)I-[Tyr(34)]hPTH-(19-84) from the C-PTH receptor, the former preparation being more potent on a molar basis, whereas hPTH-(1-34) had no effect. These results suggest that C-PTH fragments, particularly hPTH-(7-84), can influence the Ca(2+) concentration negatively in vivo and limit in such a way the calcemic responses to hPTH-(1-84) and hPTH-(1-34) by interacting with a receptor different from the PTH/PTHrP receptor, possibly a C-PTH receptor.

Carboxyl-terminal fragments of parathyroid hormone are not secreted preferentially in primary hyperparathyroidism as they are in other hypercalcemic conditions.

Calcium infusion in normal men decreases immunoreactive PTH (iPTH). Intact iPTH (I) shows the greatest decline, and there is a greater decrease in carboxyl-terminal iPTH (C) than in midcarboxyl-terminal iPTH (M); thus, C/I, M/I, and M/C ratios are increased. To verify whether this adaptive mechanism to hypercalcemia was present in patients with primary hyperparathyroidism (PHP), we measured total serum calcium (Ca), I, C, and M as well as C/I, M/I, and M/C ratios in 32 normocalcemic normal subjects (NN), in the same normal subjects made hypercalcemic (HN), in 31 patients with PHP, and in 12 patients with nonparathyroid hypercalcemia (NPHN). Eight patients with PHP and the 32 NN were submitted to CaCl2 and Na2 EDTA infusions to evaluate their parathyroid function. Ca was lower (P < 0.005) in NN (2.21 +/- 0.06 mmol/L) than in PHP (2.80 +/- 0.25 mmol/L) or NPHN (2.83 +/- 0.20 mmol/L). The HN Ca value (2.80 +/- 0.18 mmol/L) was similar to those in PHP and NPHN subjects. C, M, and I were increased in PHP compared to the other groups (P < 0.005). PHP had C/I and M/I ratios of 2.03 +/- 0.72 and 9.04 +/- 7.69, values similar to NN (2.29 +/- 0.55 and 8.70 +/- 3.0), but lower than HN (5.36 +/- 2.48 and 25.93 +/- 13.86; P < 0.005) and NPHN (11.91 +/- 13.06 and 18.69 +/- 10.81; P < 0.005). NPHN also had a lower M/C ratio than HN (2.76 +/- 2.02 vs. 4.99 +/- 1.81; P < 0.05). PHP and NN could increase their C/I ratio to the same maximum (4.71 +/- 1.26 vs. 5.70 +/- 2.94), but PHP did so at a much higher set-point (2.67 +/- 0.19 vs. 2.24 +/- 0.10 mmol/L; P < 0.005). PHP also had higher set-points for M/I, and M/C ratios even if they failed to increase the ratios to the high values in NN [M/I 11.6 +/- 6.4 vs. 29.3 +/- 18.3 (P < 0.005); M/C, 2.16 +/- 1.20 vs. 5.0 +/- 1.93 (P < 0.005)]. Thus, carboxyl-terminal fragments are not secreted preferentially in PHP as they are in other hypercalcemic conditions. This relates to a higher set-point for the regulation of C/I and M/I ratios, permitting the secretion of more intact hormone relative to C or M fragments. The lower M/C ratio in NPHN and in PHP made more hypercalcemic compared to HN suggests a lower production or a higher clearance of midcarboxyl-terminal fragments in chronic hypercalcemia.

Aberrant membrane hormone receptors in incidentally discovered bilateral macronodular adrenal hyperplasia with subclinical Cushing's syndrome.

Cortisol secretion in adrenal Cushing's syndrome can be regulated by the aberrant adrenal expression of receptors for gastric inhibitory polypeptide, vasopressin, catecholamines, LH/human CG (LH/hCG), or serotonin. Four patients with incidentally discovered bilateral macronodular adrenal hyperplasia without clinical Cushing's syndrome were evaluated for the possible presence of aberrant adrenocortical hormone receptors. Urinary free cortisol levels were within normal limits, but plasma cortisol levels were slightly elevated at nighttime and suppressed incompletely after dexamethasone administration. Plasma ACTH was partially suppressed basally but increased after administration of ovine CRH. A 51-yr-old woman had ACTH-independent increases of plasma cortisol after 10 IU AVP im (292%), 100 microg GnRH iv (184%), or 10 mg cisapride orally (310%); cortisol also increased after administration of NaCl (3%), hCG, human LH, and metoclopramide. In a 61-yr-old man, cortisol was increased by AVP (349%), GnRH (155%), hCG (252%), and metoclopramide (191%). Another 53-yr-old male increased plasma cortisol after AVP (171%) and cisapride (142%). Cortisol secretion was also stimulated by vasopressin in a 54-yr-old female. This study demonstrates that subclinical secretion of cortisol can be regulated via the aberrant function of at least V1-vasopressin, LH/hCG, or 5-HT4 receptors in incidentally identified bilateral macronodular adrenal hyperplasia.

Accumulation of a non-(1-84) molecular form of parathyroid hormone (PTH) detected by intact PTH assay in renal failure: importance in the interpretation of PTH values.

A molecular form of PTH different from PTH-(1-84) and present in normal serum is recognized by two-site intact (I-) PTH assays; it responds to Ca2+ changes in the same way that PTH carboxyl-terminal fragments do. To evaluate the impact of this finding, we have compared basal, stimulated, and nonsuppressible I-PTH values in 14 normal subjects and 15 renal failure patients, subdivided into 8 patients with low (< 12 pmol/L; LBI) and 7 with high (> 12 pmol/L; HBI) basal I-PTH. Samples obtained under various calcemic conditions in these 3 groups were further fractionated by high performance liquid chromatography (HPLC) and assayed for I-PTH, and the various peaks observed were quantitated by planimetry. Differences among the 3 groups were reinterpreted knowing the exact composition of I-PTH. Basal I-PTH was greatly increased in HBI (mean +/- SD, 44.1 +/- 38.6 pmol/L) compared to that in normal subjects (2.5 +/- 0.8 pmol/L; P < 0.001) or LBI (6.1 +/- 2.4 pmol/L; P < 0.001); the difference was less in these last 2 groups (P < 0.01). Similar differences were observed for stimulated and nonsuppressible I-PTH, except for stimulated I-PTH, which was similar in normal and LBI subjects. Two I-PTH HPLC molecular forms accounted for I-PTH immunoreactivity in the 3 groups. In normal subjects, PTH-(1-84) accounted for 74.9 +/- 4.3%, 79.0 +/- 3.0%, and 87.2 +/- 1.0% of I-PTH in hyper-, normo-, and hypocalcemia, respectively, but only for 44.6 +/- 2.5%, 50.5 +/- 0.7%, and 63.6 +/- 0.1% in renal failure patients, with similar results in HBI and LBI. The accumulation of a non-(1-84) PTH peak accounted for the difference between normal subjects and renal failure patients. When basal, stimulated, and nonsuppressible I-PTH values were separated into their 2 components, prior differences between HBI and LBI or normal subjects remained unchanged because of very high I-PTH values in HBI, but differences between normal and LBI subjects were entirely explained by the accumulation of the non-(1-84) PTH peak [basal, 3.0 +/- 1.2 vs. 0.5 +/- 0.2 pmol/L (P < 0.001); stimulated, 6.8 +/- 2.3 vs. 2.3 +/- 1.0 pmol/L (P < 0.001); nonsuppressible, 1.3 +/- 0.7 vs. 0.2 +/- 0.08 pmol/L (P < 0.001)]; PTH-(1-84) values were similar (basal, 3.1 +/- 1.2 vs. 2.0 +/- 0.6 pmol/L; stimulated, 12.0 +/- 3.9 vs. 15.5 +/- 6.6 pmol/L; nonsuppressible, 1.1 +/- 0.6 vs. 0.52 +/- 0.22 pmol/L). Thus, a non-(1-84) PTH molecular form detected by two-site I-PTH assays accumulates in renal failure and accounts for a larger proportion of I-PTH than that in normal subjects. Levels of I-PTH 1.57 times higher than those in normocalcemic subjects are thus required in renal failure to achieve similar PTH-(1-84) concentrations. The composition of I-PTH is also identical in all hemodialyzed patients.

The set point of parathyroid hormone stimulation by calcium is normal in progressive renal failure.

An increased set point of PTH stimulation by ionized calcium (Ca++) has been observed in renal failure patients with severe secondary hyperparathyroidism. The extension of this concept to all renal failure patients has remained problematic, even if it could explain elevated PTH levels in the absence of other biochemical abnormalities. We were particularly interested in seeing whether the concept could fit patients with progressive renal failure (PRF). To achieve this, we studied 26 normals (N), 9 patients with PRF, and 12 hemodialyzed patients (HD) in the basal state and during parathyroid function tests. The latter two groups were studied at the end of winter and end of summer, respectively. Patients with PRF had normal levels of Ca++, PO4, and 1,25(OH)2D, and they had low-normal concentrations of 25(OH)D; their basal I- and C-PTH levels were 3- and 4-fold higher than N, as were their creatinine levels. HD had significantly lower levels of Ca++ and 1,25(OH)2D, and they had higher levels of phosphate, creatinine, I-PTH, and C-PTH than N or PRF. Stimulated levels of I-PTH were similar in N (13.6 +/- 4.3 pmol/L) and PFR (18 +/- 3.3 pmol/L) and elevated in HD (37.1 +/- 28.7 pmol/L; P < 0.001 vs. N, and P < 0.05 vs. PRF). Nonsuppressible I-PTH was increased 2-fold in PRF (N = 0.64 +/- 0.19 vs. PRF = 1.28 +/- 0.46 pmol/L; P < 0.01) and 6-fold in HD (3.95 +/- 2.85 pmol/L; P < 0.001 vs. others). But the set point of I-PTH stimulation by Ca++ was normal in PRF (N = 1.18 +/- 0.03 vs. PRF = 1.20 +/- 0.04 mmol/L; not significant) and decreased in HD (1.09 +/- 0.04 mmol/L; P < 0.001 vs. others). Similar results were obtained with the set point of C-PTH and of the C-PTH/I-PTH ratio. A positive correlation was observed between serum Ca++ concentration and the set point value when all three populations were analyzed together (r = 0.759, n = 47, P < 0.0001). These results indicate that the set point of PTH stimulation is normal in PRF and decreased in hypocalcemic HD. The set point seems to adjust to the ambient Ca++ concentration of the patients, by mechanisms yet to be elucidated. This does not suggest participation of this factor to the genesis of the secondary hyperparathyroidism of PRF.

The modulation of circulating parathyroid hormone immunoheterogeneity in man by ionized calcium concentration.

Twenty normal individuals received 2-h iv infusions of CaCl2 and Na2 ethylenediamine tetra-acetate, with sampling every 15 min. PTH was measured by means of an intact hormone assay (I) and two carboxylterminal assays structured to react mostly with mid (M) or late (L) carboxylterminal fragments. A mathematical model was used to fit the sigmoidal relationship between ionized calcium (CA++) and PTH values. The influence of Ca++ on circulating PTH immunoheterogeneity was assessed via changes in L/I, M/I, and M/L ratios. Results are reported as means +/- SD. Response to hypocalcemia was highest with M (57.8 +/- 26.4 pmol/L, P less than 0.005 vs. L or I) and higher with L (20.1 +/- 5.6 pmol/L; P less than 0.0005 vs. I) than with I (14.1 +/- 6.4 pmol/L). L/I, M/I, and M/L decreased from 2.43 +/- 0.56 to 1.54 +/- 0.19 (P less than 0.0005), 8.44 +/- 2.38 to 4.36 +/- 4.07 (P less than 0.0005), and 3.49 +/- 0.71 to 2.86 +/- 0.76 (P less than 0.005), respectively, during Na2 ethylenediamine tetra-acetate infusion. Nonsuppressible PTH was again higher with M (13.7 +/- 4.8 pmol/L; P less than 0.0005 vs. L or I) and higher with L (2.8 +/- 0.7 pmol/L, P less than 0.0005 vs. I) than with I (0.5 +/- 0.3 pmol/L). L/I, M/I, and M/L ratios increased from 2.47 +/- 0.97 to 5.35 +/- 2.09 (P less than 0.0005), 8.90 +/- 3.10 to 29.56 +/- 14.89 (P less than 0.0005), and 3.62 +/- 0.90 to 5.30 +/- 1.91 (P less than 0.005) during CaCl2 infusion. The set-point for PTH stimulation by calcium was similar for M (1.15 +/- 0.035 mmol/L) and L (1.175 +/- 0.041 mmol/L) but significantly higher with the I assay (1.184 +/- 0.31 mmol/L; P less than 0.0005 vs. M). The M/I, L/I, and M/L ratio set-points were similar at 1.28 +/- 0.01, 1.27 +/- 0.01, and 1.29 +/- 0.02 mmol/L. Thus, even if proportionately more intact PTH and less carboxylterminal fragments are produced and secreted during hypocalcemia, the latter still predominate in the circulation. Furthermore, at high calcium values, secretion of fragments is less well inhibited than that of intact hormone. The lower secretion and higher ratio set-points suggest that the secretion and intracellular degradation of PTH have different sensitivities to inhibition by calcium.

Hypocalcemia induced during major and minor abdominal surgery in humans.

Hypocalcemia has only been rarely reported during surgical procedures not involving massive blood transfusions. The frequent observation in our hospital of a low serum ionized calcium level during surgery in nonacutely ill patients prompted us to investigate the calcium-PTH axis in three groups of subjects undergoing major (hepatectomy; n = 10), moderately severe, or minor surgery under general anesthesia (colectomy; n = 7, herniorrhaphy; n = 9) compared to that in one group of minor surgery cases under epidural anesthesia (herniorrhaphy; n = 15). Serum samples were obtained before anesthesia, after anesthesia but before surgery, and 40 and 120 min after the beginning of surgery in all groups of patients and for up to 3 days in major and moderately severe cases. Significant falls (P < 0.01), always proportional to the severity of the surgical/anesthesia procedure, were observed for ionized calcium (6-20%), total calcium (8-19%), and albumin (8-23%) accompanied by increases in intact PTH (105-635%). The decrease in ionized and total calcium correlated with a decrease in albumin (P < 0.001). Phosphorus, pH, and magnesium levels remained within the normal range. Adjustment of ionized calcium for variation in albumin revealed that 50-100% of the variation in ionized calcium could be attributed to a fall in albumin resulting from fluid administration to patients before admission to the surgery ward and between the onset of anesthesia and the end of surgery (1.2-5.6 L). Albumin- and pH-independent residual ionized calcium decreases of 12.2% in the hepatectomy group, 4.6% in the group of moderately severe and minor cases under general anesthesia, and 3.7% in the control group reflected the severity of the surgical/anesthesia procedure.

Estrogen replacement decreases the set point of parathyroid hormone stimulation by calcium in normal postmenopausal women.

Estrogens decrease serum total and ionized calcium (Ca) concentrations in postmenopausal women with or without primary hyperparathyroidism, but cause little or no increase in serum PTH suggesting a modification of the relationship between the two. In order to define this relationship, we studied the effect of conjugated estrogens on total and ionized serum Ca and serum PTH concentrations in five normal postmenopausal women, before and after 3, 11, and 23 weeks of therapy. Dynamic tests of parathyroid gland function, based on 2-h iv infusions of CaCl2 and NaEDTA, were performed at each time. Total and ionized serum Ca and carboxylterminal PTH were measured every 15 min during the infusions, and parathyroid function was evaluated by a nonlinear 4-parameter mathematical model. Estrogen therapy caused decreases in serum total [2.36 +/- 0.04 (SD) mmol/L, baseline vs. 2.19 +/- 0.05 mmol/L, 23 weeks, P less than 0.005) and ionized calcium (1.27 +/- 0.01 mmol/L, baseline vs. 1.21 +/- 0.02 mmol/L, 23 weeks, P less than 0.005]; the decreases were evident at 3 weeks and persisted for the duration of the study. Serum PTH concentrations did not change (8.94 +/- 1.84 pmol/L, baseline vs. 8.98 +/- 2.38 pmol/L, 23 weeks). Three parameters of the parathyroid function, the maximal response to hypocalcemic stimulation, the nonsuppressible fraction of circulating PTH, and the slope of PTH on calcium at the set point were not affected by estrogen treatment. The fourth parameter, the set point of PTH stimulation by serum total calcium (2.16 +/- 0.04 mmol/L, baseline vs. 1.97 +/- 0.07 mmol/L, 23 weeks, P less than 0.0166) or by serum ionized Ca (1.19 +/- 0.04 mmol/L, baseline vs. 1.12 +/- 0.03 mmol/L, 23 weeks, P less than 0.01), was decreased by estrogen treatment. This was evident at the earliest time point studied and persisted thereafter. The decrease in ionized Ca set point only explained 40% of the decrease in total calcium set point, the remaining 60% being related to hemodilution of plasma protein during therapy. We conclude that estrogen replacement can influence parathyroid function in postmenopausal women by resetting the set point of PTH stimulation by ionized Ca. This in turn could contribute to the estrogen-induced changes in their Ca balance.