A novel renal carbonic anhydrase type III plays a role in proximal tubule dysfunction.

Dysfunction of the proximal tubule (PT) is associated with variable degrees of solute wasting and low-molecular-weight proteinuria. We measured metabolic consequences and adaptation mechanisms in a model of inherited PT disorders using PT cells of ClC-5-deficient (Clcn5Y/-) mice, a well-established model of Dent's disease. Compared to cells taken from control mice, those from the mutant mice had increased expression of markers of proliferation (Ki67, proliferative cell nuclear antigen (PCNA), and cyclin E) and oxidative scavengers (superoxide dismutase I and thioredoxin). Transcriptome and protein analyses showed fourfold induction of type III carbonic anhydrase in a kidney-specific manner in the knockout mice located in scattered PT cells. Kidney-specific carbonic anhydrase type III (CAIII) upregulation was confirmed in other mice lacking the multiligand receptor megalin and in a patient with Dent's disease due to an inactivating CLCN5 mutation. The type III enzyme was specifically detected in the urine of mice lacking ClC-5 or megalin, patients with Dent's disease, and in PT cell lines exposed to oxidative stress. Our study shows that lack of PT ClC-5 in mice and men is associated with CAIII induction, increased cell proliferation, and oxidative stress.

Mapping the gene causing X-linked recessive nephrolithiasis to Xp11.22 by linkage studies.

X-linked recessive nephrolithiasis is associated with kidney stones and renal tubular dysfunction in childhood progressing to renal failure in adulthood. The primary defect causing this renal tubular disorder is unknown and determining the chromosomal location of the mutant gene would represent an important step toward defining the biochemical basis. We have performed linkage studies in 102 members (10 affected males, 47 unaffected males, 15 obligate heterozygote females, and 30 unaffected females) from five generations of one family. As genetic markers we used 10 cloned human X chromosome fragments identifying restriction fragment length polymorphisms and seven pairs of oligonucleotide primers identifying microsatellite polymorphisms. Linkage with the locus DXS255 was established with a peak LOD score = 5.91 at 3.6% recombination, thereby localizing the X-linked recessive nephrolithiasis gene to the pericentromeric region of the short arm of the X chromosome (Xp11.22). Multilocus analysis indicated that the mutant gene was distal to DXS255 but proximal to the Duchenne muscular dystrophy locus on Xp. Thus, the gene that causes X-linked recessive nephrolithiasis maps to the pericentromeric region of the short arm of the X chromosome (Xp11.22), and further characterization of this gene will help to elucidate the factors controlling renal tubular function and mineral homeostasis.

Quantitative evaluation of anticalciuretic effects of synthetic parathyroid hormonelike peptides.

The PTH-like peptide (PTHLP) responsible for hypercalcemia in many patients with humoral hypercalcemia of malignancy (HHM) acts on PTH receptors in bone and kidney, and large doses of PTHLPs have been shown to reduce urinary calcium excretion. However, PTHLPs have not been assessed quantitatively for effects on renal calcium excretion at concentrations (5-100 pM) now known to be found in the serum of patients with HHM. We perfused isolated rat kidneys with synthetic [tyr-36] PTHLP-(1-36)amide [PTHLP-(1-36)], PTHLP-(1-74), and synthetic bovine PTH-(1-34). The ratio of calcium to sodium clearances (CCa/CNa), a measure of distal tubular calcium transport, was reduced to the same extent by PTH, PTHLP-(1-36), and PTHLP-(1-74) (54.3 +/- 3.9, 52.9 +/- 3.9, and 52.7 +/- 1.3% reductions from control), respectively) at maximal doses (35-50 pM and higher), with half-maximal effects at 10, 18, and 32 pM, respectively. PTH, PTHLP-(1-36), and PTHLP-(1-74) all increased fractional phosphate excretion over control (p less than 0.05 each). All three peptides were natriuretic, at least doubling fractional Na excretion (p less than 0.05 or less). Urinary cAMP excretion was increased by all three. None had any effect on GFR or renal vascular resistance. These results indicate that clinically relevant concentrations of PTHLPs are anticalciuretic and natriuretic, with maximal effects similar to those of PTH. Differences in anticalciuretic potencies are small but may explain differences among patients, depending on the size(s) and concentrations of the native circulating form(s) of the peptide.

In vitro stimulation of thyroid ornithine decarboxylase activity and polyamines by thyrotropin.

Thyrotropin (TSH) stimulation of ornithine decarboxylase (ODC) activity and polyamine levels was studied in vitro in rat thyroids. The elevation in ODC activity was related to the concentration of TSH in the incubation medium with peak activity at a concentration of 25mU/ml. ODC activity with 50 mU/ml of TSH was 3 to 5-fold higher than control activity at 5 h of incubation; this stimulation was enhanced by the addition of 0.5 mM 3-isobutyl-l-methyl xanthine (MIX), a phosphodiesterase inhibitor. Dibutyryl cyclic AMP (DbcAMP) also stimulated ODC activity with a dose response up to 2.0 mm. The increase in ODC activity with TSH and MIX was prevented by incubation with actinomycin D (10 microgram/ml) or puromycin (0.2 mM). Putrescine concentrations in rat thyroids rose to three times basal levels after 6 h of incubation with TSH and MIX; no significant elevation in spermidine or spermine was observed after up to 7 h incubation. The increase in tissue putrescine preceded a rise in [3H]uridine incorporation into acid-soluble material that occurred at 7 h. The results suggest that stimulation of thyroid ODC activity by TSH is mediated by a cyclic AMP; the data further are consistent with a role for polyamines in the control of RNA synthesis in the thyroid.

Marked hypotonic polyuria resulting from nephrogenic diabetes insipidus with partial sensitivity to vasopressin.

We studied two women with severe hypotonic polyuria whose symptoms dated from infancy. We eliminated the possibility of central diabetes insipidus (DI) and primary polydipsia, and established the presence of nephrogenic DI on the basis of: 1) the interrelationships between plasma osmolality, urine osmolality, and urinary AVP; and 2) impaired antidiuretic responses to AVP and 1 deamino-8-D-arginine vasopressin. Though 25-50 times as resistant to 1 deamino-8-D-arginine vasopressin nasal spray as patients with central DI, these patients could be treated effectively with large doses of the nasal spray. One patient has been so treated for more than a year with dramatic improvement in her polydipsia, polyuria, and sense of well-being.

Ectopic secretion of neurohypophyseal peptides in patients with malignancy.

A great deal of information has been accumulated on the synthesis and release of AVP, oxytocin, and their associated neurophysins under normal circumstances. In 1957, Schwartz and Bartter first described SIAD in patients with lung cancer and postulated that the clinical findings were the results of excessive vasopressin secretion. Tumors have been known since 1964 to produce vasopressin, and small cell (oat cell) carcinoma of the lung is by far the most frequent malignant cause of SIAD. The biosynthetic pathway for the synthesis of AVP and its associated neurophysin (and to a lesser extent, oxytocin and its neurophysin) is well described and is similar if not identical to the synthesis of these peptides in the hypothalamus. However, there is little reliable information on the control of peptide synthesis and release by these tumors. The clinical picture of SIAD is well described and occurs in 20% to 40% of patients with SCCL, although up to 88% of patients with extensive SCCL have elevated circulating levels of one or more neurohypophyseal peptides. This information has led to considerable interest in the use of these peptides as tumor markers for the diagnosis, evaluation, and assessment of therapy in these patients. With the recognition of the high incidence of secretion of neurohypophyseal peptides by SCCL, studies have been initiated to determine the value of radioactive vasopressin neurophysin antibodies in localizing tumors that synthesize these peptides. The studies provide potentially useful information in diagnosing and following patients with SCCL and also offer some promise that radiolabeled antineurophysins could eventually be used to treat these patients.

Nephrolithiasis.

Genetic factors are important determinants for kidney stone formation. Cystinuria, primary hyperoxaluria, and X-linked nephrolithiasis (Dent's disease) are monogenic kidney stone diseases for which responsible genes have been identified. Familial stone disease with hyperuricosuria or renal tubular acidosis has been described in several clinical settings. Idiopathic hypercalciuria is the most common stone risk factor, and evidence in humans and in a rat model indicates that hypercalciuria is a complex, polygenic trait. Some candidate genes for idiopathic hypercalciuria are suggested by the known physiology, including those encoding the vitamin D receptor, the 1 alpha-hydroxylase of vitamin D, the calcium-sensing receptor, the renal sodium-dependent phosphate transporter, and chloride channels, but others remain to be identified. The multifaceted physiology of hypercalciuria may reflect the combined effects of polymorphisms in several genes.

Hereditary vasopressin resistance in man and mouse.

The DI +/+ Severe hereditary nephrogenic diabetes insipidus mouse is resistant to the antidiuretic action of vasopressin (VP) because of failure to accumulate cAMP and subsequent inability to form intramembranous particles on the apical (luminal) surface of kidney cells that normally respond to VP. The defect is primarily, if not exclusively, due to excessive activity of specific cAMP-phosphodiesterases. The abnormality can be overcome in vitro and in vivo by the phosphodiesterase inhibitor, rolipram. Most cases of hereditary NDI in man have sex-linked recessive inheritance, which appears to be due to an abnormality of the V2 receptor. The chromosomal locus of the defect is Xq28. Sporadic cases of congenital NDI have been described in females who appear to have a defect beyond the V2 receptor and the guanine nucleotide-binding stimulatory protein. There is no information on the biochemical defect in very rare cases with other types of inheritance patterns. No abnormalities of V1a and V1b receptor function have been found in patients with NDI. Mice and patients with NDI have evidence of increased AVP synthesis. AVP release in relation to plasma osmolality is increased in patients during infusion of hypertonic saline. This is the opposite of what has been described in patients with primary polydipsia (dipsogenic diabetes insipidus) who are chronically overhydrated. Together, these studies indicate that chronic dehydration and overhydration can cause up- and downregulation of the osmotic release of AVP.

Hypercalcemia with excess serum 1,25 dihydroxyvitamin D in lymphomatoid granulomatosis/angiocentric lymphoma.

Hypercalcemia has been described in a variety of granulomatous and lymphoproliferative disorders in association with elevated serum levels of 1,25-dihydroxyvitamin D. In such cases, hypercalcemia appears to be the consequence of excessive production of 1,25(OH)2D by the lymphocyte/macrophage line. The authors report a patient with lymphomatoid granulomatosis/angiocentric lymphoma who developed hypercalcemia with extreme elevation in serum 1,25(OH)2D. Therapy with steroids reduced the serum calcium and 1,25(OH)2D levels to normal. Hypercalcemia has not previously been reported in lymphomatoid granulomatosis/angiocentric lymphoma. The distinctive features of this malignancy, and the derangement in the metabolism of 1,25(OH)2D in lymphoproliferative disorders in general, are discussed.

New insights into causes and treatments of kidney stones.

Recent findings have provided insight into the molecular basis of kidney stone formation and entirely changed our approach to management of calcium stones. Understanding the role of genetic factors and the various promotors and inhibitors of stone formation should lead to more effective prophylaxis and treatment of other types of stones as well.

Effects of confluence on phosphate transport capacity in cultured renal cell lines.

The LLC-PK1 cell line transports phosphate (Pi), glucose, and amino acids using carriers similar to those in proximal tubular cells. Others have reported that when monolayers reach confluence, hexose transport increases and activity of the A-amino acid transporter falls. The present study evaluates Pi uptake by two continuous cell lines derived from renal proximal tubule, and demonstrates that phosphate uptake falls sharply upon reaching confluence in LLC-PK1 cells but not in cultured opossum kidney (OK) cells. The fall in Pi uptake in LLC-PK1 cells at confluence represents a halving in Vmax for Na-dependent phosphate uptake (2.33 vs. 5.00 nmol/mg protein/5 min) without a change in Km (82 vs. 94 microM). Suppression of phosphate transport in confluent monolayers of LLC-PK1 cells is completely reversed by bringing the cells into suspension. As has been shown for the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA), exposure of monolayers to serum stimulates phosphate uptake, but unlike phorbol ester, serum does so without stimulating alanine uptake. OK cells differ from LLC-PK1 in that no change occurs in Pi uptake at confluence, although they resemble LLC-PK1 cells in that sugar uptake rises and alanine uptake falls at confluence. The different temporal patterns for Pi uptake in the two cell lines indicates that developmental change in the uptake of Pi is not linked to that of glucose or alanine.

Xanthine effects on renal proximal tubular function and cyclic AMP metabolism.

We evaluated the renal effects of xanthines using two in vitro models: the isolated perfused rat kidney (IPRK) and cultured opossum kidney (OK) cells, a continuous cell line that resembles proximal tubule and responds to parathyroid hormone (PTH). 1,3-Diethyl-8-phenylxanthine (DPX) a potent adenosine receptor antagonist, increased urine volume, glomerular filtration rate, vascular resistance and the fractional excretions of Na, K, Ca and Pi in the IPRK. DPX lowered the Na-dependent uptake of Pi by OK cells. By comparison enprofylline, 3-propylxanthine (ENP), a weak adenosine receptor antagonist, produced a slight elevation in glomerular filtration rate but no changes in electrolyte excretion by IPRK or Pi uptake by OK cells. Both DPX and ENP produced negligible elevations in basal IPRK cAMP. A 1-nM bolus of PTH elevated urinary and perfusate cAMP 50- and 10-fold, respectively. PTH-elevated urinary and perfusate cAMP were augmented further 4- to 7-fold with DPX and 3- to 4-fold with ENP (All IPRK experiments used 50 microM xanthine). OK cells produced a 2-fold cAMP response to 10 nM PTH alone. OK cells treated with 50 microM DPX exhibited no increase in basal but a 13-fold increase in PTH-stimulated cell cAMP. The rank order of potency at 50 microM to augment OK cell cAMP with 10 nM PTH was DPX greater than 1,3-dipropyl-8-cyclopentylxanthine (DPC) greater than 1-methyl-3-isobutylxanthine greater than theobromine greater than theophylline greater than caffeine greater than ENP = no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of perfusate phosphate concentration on responses to PTH in isolated rat kidney.

We studied the excretion of electrolytes and adenosine 3',5'-cyclic monophosphate (cAMP) by rat kidneys perfused for 2 or 3 h at several concentrations of phosphate (Pi). Fractional phosphate excretion increased with higher perfusate Pi concentrations (up to 4.0 mM Pi) without parathyroid hormone (PTH), but no tubular maximum for phosphate reabsorption was reached. The addition of synthetic bovine 1-34 PTH (bPTH) gave a dose-related phosphaturia that depended on the perfusate Pi level. The urinary cAMP response to doses of bPTH was highly dependent on perfusate Pi concentration: with 20 nM bPTH, urinary cAMP was 211 +/- 94 pmol/ml glomerular filtration rate at 1.2 mM Pi and was 3,998 +/- 711 at 4.0 mM Pi (P less than 0.001). Without bPTH, cAMP excretion did not differ among Pi levels. Calcium-to-sodium clearance ratio rose with time in kidneys perfused without bPTH but fell with the addition of as little as 0.02 nM bPTH, regardless of Pi concentration. Variations in Pi or bPTH did not affect fractional magnesium excretion, which fell by 68% through 3 h of perfusion (P less than 0.001). These data suggest that the effects of Pi concentration on renal electrolyte excretion are consistent with changes in the filtered Pi load but that extracellular Pi concentrations dramatically alter the renal cAMP response to bPTH in the isolated perfused kidney.

Acute cardiac failure and hepatic ischemia induced by disopyramide phosphate.

Two patients abruptly developed congestive heart failure and elevation in serum transaminase levels when given disopyramide phosphate; enzyme abnormalities and hemodynamic status corrected upon withdrawal of the drug. Both patients had underlying ischemic cardiomyopathy. Myocardial infarction, pulmonary embolism, and viral hepatitis were ruled out in both patients. One patient had a liver biopsy documenting central hepatic necrosis with congestion, consistent with hepatic ischemia and not toxic hepatitis. In the other patient, cardiac decompensation and hepatocellular enzyme elevation were reproduced on rechallenge with the drug. Disopyramide should be used with caution in patients with heart failure.

Effects of (Sp)- and (Rp)-adenosine cyclic 3',5'-phosphorothioates on electrolyte excretion by the isolated perfused rat kidney.

We studied the effects of the (Sp) and (Rp) diastereomers of the phosphorothioate analogue of cyclic AMP (cAMPS) on the excretion of electrolytes in the isolated perfused rat kidney. cAMPS is highly permeant across the peritubular cell membrane and is not metabolized by the rat kidney (Coulson et al., Life Sci. 32: 1489-1498, 1983). Addition of 10 microM cAMPS(Sp) to the perfusate resulted in a significant phosphaturia, bicarbonaturia, magnesuria and natriuresis and no change in renal vascular resistance or glomerular filtration rate. Fractional excretion of calcium was elevated by cAMPS(Sp) but proportionately less than the fractional excretion of sodium so that the ratio of calcium to sodium clearances was significantly lowered. cAMPS(Rp) 10 or 100 microM was without effect on renal electrolyte excretion. The parathyroid hormone-like effects of the (Sp) diastereomer are consistent with its known ability to activate protein kinase.

X-linked recessive nephrolithiasis: presentation and diagnosis in children.

We report a new X-linked recessive nephrolithiasis kindred. X-linked recessive nephrolithiasis is a recently described disease characterized by recurrent nephrolithiasis, nephrocalcinosis, and progressive renal failure, associated with mutations in a renal chloride channel gene, chloride channel number 5. Screening individuals at risk with renal ultrasonography and measurement of urinary excretion of low molecular weight proteins and calcium will exclude boys without X-linked recessive nephrolithiasis kindred and identify boys likely to have the disease.

Antidiuretic and PGE2 responses to AVP and dDAVP in subjects with central and nephrogenic diabetes insipidus.

Vasopressin stimulates renal prostaglandin (PGE2) production at several loci and in turn PGE2 modulates the antidiuresis. We have found the time courses of increased urinary PGE2 in subjects with central diabetes insipidus (DI) parallel the antidiuretic responses to AVP and dDAVP. The antidiuretic response to 4 micrograms dDAVP in these subjects was far greater than the response to 5 U (12.5 micrograms) AVP, but the PGE2 response to the dDAVP was only marginally greater than that which followed the AVP. Therefore, dDAVP disproportionately stimulates antidiuresis in relation to PGE2 production, whereas the reverse holds for AVP. In subjects with nephrogenic DI 12.5 micrograms AVP caused no antidiuresis but stimulated PGE2 excretion as well as in subjects with central DI. There was an intermediate relationship between antidiuresis and PGE2 excretion in subjects with central DI given AVP and subjects with nephrogenic DI injected with dDAVP. In summary, 1) the normal PGE2 response to AVP in subjects with nephrogenic DI is consistent with other evidence that non-antidiuretic actions of vasopressin are not impaired in these subjects. 2) The limited capability of dDAVP to stimulate PGE2 may be a factor in the augmented antidiuretic response to dDAVP in subjects with central DI. 3) Antidiuretic and PGE2 responses to vasopressin can be dissociated, thus allowing further consideration of mechanisms by which each may be independently controlled and interrelated.

Effects of atrial natriuretic peptides on metabolism of arginine vasopressin by isolated perfused rat kidney.

Atrial natriuretic peptide (ANP) antagonizes the release and action of arginine vasopressin (AVP) both in vivo and in vitro. We have reported that ANP increases the urinary and metabolic clearances of AVP in normal subjects (A. M. Moses et al. J. Clin. Endocrinol. Metab. 70: 222-229, 1990). To clarify this effect, we perfused isolated rat kidneys in vitro and measured the clearances of AVP for 30 min after the addition of rat ANP [rANP-(1-28), 10(-7) M]. In the perfused kidney, rANP increased the urinary clearance of AVP (UCAVP) from 321 +/- 19 to 417 +/- 20 microliters/min (P less than 0.01) and increased the glomerular filtration rate (GFR) from 558 +/- 28 to 696 +/- 28 microliters/min (P less than 0.01). Fractional excretion of AVP was unchanged. Rates of AVP reabsorption were directly related to filtered AVP, and this relationship was not altered by ANP. ANP did not affect the total organ clearance or the renal metabolic clearance of AVP. The increase in GFR was associated with increases in renal vascular resistance (P less than 0.05), filtration fraction (P less than 0.01), and sodium excretion (P less than 0.001). UCAVP also increased when GFR was raised without ANP by perfusing at higher pressures. The rat ANP clearance receptor agonist [cANP- (4-23), 10(-7) M] did not change GFR or UCAVP. ANP increases UCAVP in the isolated perfused rat kidney. This appears to be a hemodynamic effect of ANP, acting through its biological receptor and not the clearance receptor.(ABSTRACT TRUNCATED AT 250 WORDS)