Circadian rhythm in serum parathyroid hormone concentration in human subjects: correlation with serum calcium, phosphate, albumin, and growth hormone levels.

A circadian variation in serum calcium, albumin and PTH concentration in normal subjects has been demonstrated. The levels of the three blood constituents were remarkably constant during the day, but striking night and early morning changes occurred. Serum calcium levels were highest at 8:00 p.m. and reached a nadir between 2:00 and 4:00 a.m. Serum albumin levels were parallel to those of serum calcium. PTH levels began to rise after 8:00 p.m., reached the highest levels between 2:00 and 4:00 a.m., and fell to baseline values by 8:00 a.m. The nocturnal fall in serum calcium levels appears to be secondary to dilution of serum proteins by increasing blood volume. The nocturnal rise in PTH levels appears to be independent of serum calcium levels within the normal range but it can be abolished by induced hypercalcemia. Serum phosphate levels were lowest between 8:00 a.m. and 10:00 a.m. and highest between 2:00 a.m. and 4:00 a.m. The data presented suggest that circadian changes in serum phosphate levels are not mediated in toto by parathyroid hormone but they are exaggerated when the secretion of this hormone is inhibited. They are independent of growth hormone levels and activity but they are greatly modified during a prolonged fast.

Inhibitory effect of prostaglandin F2 alpha on the growth of a hormone-dependent rat mammary tumor.

Growth of the rat hormone-dependent mammary adenocarcinoma MTW-9 was inhibited by prostaglandin F2alpha (PGF2alpha) This inhibition of tumor growth was associated with a marked reduction in serum progesterone concentrations. The inhibitory effect of PGF2alpha on tumor growth was abolished by concomitant injections of progesterone. The growth rates of coimplanted prolactin-secreting pituitary tumor MtTW-5 and plasma concentrations of prolactin and estradiol were not affected significantly by PGF2alpha. Our data imply that the effect of PGF2alpha on growth of rat mammary adenocarcinoma is mediated by progesterone.

Abnormalities in the regulation of growth hormone in chronic renal failure.

Carbohydrate intolerance is a common abnormality in patients with chronic renal failure. In this group of patients we investigated the interrelation among glucose, insulin, and growth hormone and confirmed the presence of carbohydrate intolerance and hyperinsulinemia. In addition we demonstrated alterations in growth hormone regulation, characterized by (1) the lack of suppression of growth hormone by orally induced hyperglycemia and paradoxical increase in serum levels of growth hormone after the administration of intravenous glucose or glucagon; (2) lack of release of growth hormone with induced hypoglycemia and an exaggerated response to levodopa administration. Furthermore, thyrotrophin-releasing hormone stimulated growth hormone release, a phenomenon not observed in the control population. Our studies show an impaired hypothalamic regulation of growth hormones secretion in patients with renal failure undergoing long-term hemodialysis.

Evaluation of the hypothalamic hypophyseal adrenal axis in patients receiving long-term hemodialysis.

Several alterations are present in the hypothalamic hypophyseal regulation of many hormones in patients with chronic renal failure. Evaluation of the hypothalamic hypophyseal adrenal axis in these groups of patients demonstrated normal levels of plasma cortisol. Dexamethasone suppression is abnormal after administration of 1 mg of oral dexamethasone, but normal after 3 mg. Dexamethasone blood levels were lower than the control after administration of 1 mg of oral dexamethasone. A dexamethasone metabolic clearance showed a similar half-life between the patients and controls. Oral absorption study showed poor absorption of the drug. Therefore, there is a problem of gastrointestinal absorption producing the abnormal dexamethasone suppression test in patients with renal failure. Results of metyrapone tests were normal. Corticotropin stimulation tests elicited a normal response. Insulin-induced hypoglycemia does not produce an increment in plasma cortisol or adrenocorticotropic hormone levels.

Single-dose metyrapone test: review of a four-year experience.

Subnormal plasma 11-deoxycortisol (compound S) responses to metyrapone were found in patients with adrenal insufficiency or with Cushing syndrome caused by adrenal tumors and in those receiving long-term glucocorticoid or diphenylhydantoin sodium therapy. High normal or exaggerated responses were seen in women receiving oral contraceptives, patients with Cushing syndrome caused by adrenal hyperplasia, and those with untreated hypothyroidism. Diabetes mellitus, hypoglycemia, congestive failure, and obesity also were associated with exaggerated responses. Subnormal plasma S responses were observed in 15 patients who responded normally to a repeat test or to the standard metyrapone test. The abnormal response resulted from insufficient metyrapone, administration at the wrong time, or delay in obtaining the blood sample. The single-dose metyrapone test may be the procedure of choice in screening for adrenal insufficiency.

Prostaglandins activation of erythropoietin production and erythroid progenitor cells.

A model is presented postulating a role for prostaglandins E and prostacyclin in kidney generation of erythropoietin and the activation of the erythroid progenitor cell (CFU-E) compartment by erythropoietin (Ep). Several criteria have been met to prove that prostanoids mediate erythropoiesis: 1) several E-type prostaglandins (PGE2, 15-methyl prostaglandin E2, 16,16-dimethyl E2, 6-keto-E1 and PGE1) produced a significant increase in radioiron incorporation in red cells of exhypoxic polycythemic mice; 2) prostaglandin E2 increased kidney production of erythropoietin in the isolated perfused dog kidney; 3) arachidonic acid, a precursor for all bisenoic prostaglandins, increased kidney production of erythropoietin in the isolated perfused dog kidney which was blocked by pretreatment with the cyclo-oxygenase inhibitor drug indomethacin; 4) hypoxemic perfusion of the isolated perfused dog kidney increased kidney production of erythropoietin and produced an elevation in prostacyclin in the perfusates; 5) albuterol, a beta-2 adrenergic agonist, produced a significant increase in perfusate levels of erythropoietin and PGE in the isolated perfused dog kidney; 6) renal ischemia increased Ep and PGE levels in renal venous plasma which was blocked by pretreatment with indomethacin; 7) prostaglandin E2 and arachidonic acid produced a significant increase in erythroid colonies (CFU-E) in vitro in normal mouse bone marrow; 8) E-type prostaglandins (15-methyl E2) increased in vivo erythroid colony (CFU-E) formation in bone marrows of post-hypoxic polycythemic mice; and 9) injections of 15-methyl E2 daily for six weeks in normal and hypoxic mice produced a significant elevation in the total circulating red cell mass. These studies indicate that hypoxic stimulation of kidney production of erythropoietin may be related to the generation of prostacyclin (PGI2). On the other hand, albuterol and ischemic (reduction in renal blood flow) stimulation of kidney production of erythropoietin involves prostaglandins of the E type. In addition, E-type prostaglandins were found to enhance the effects of erythropoietin in activating erythroid progenitor cells (CFU-E) in the bone marrow. We postulate from our model that prostaglandins E and prostacyclins are involved in the mechanism of kidney production of erythropoietin as well as the activation of the Ep-responsive cell (ERC) compartment.

The role of iodine in the pathogenesis of thyroid enlargement in rats with chronic renal failure.

In rats with mild renal failure produced by a 2/3 nephrectomy on one side followed by a total nephrectomy on the other, ingestion of a high (10 mg/kg) iodine diet for two months resulted in thyromegaly, high serum iodine levels and a good correlation between thyroid weight and serum iodine (r = 0.75, P less than 0.01) or thyroid weight and blood urea nitrogen (r = 0.745, P less than 0.01). Iodine may potentiate the effects of unidentified gointrogens that accumulate in rats with renal failure. Since the serum iodine levels were higher in the animals with renal failure, it is also possible that iodine alone may have been responsible for the observed differences in thyroid weight.

Effect of indomethacin on the hypothalamic-pituitary-adrenal axis in man.

The effect of the cyclo-oxygenase inhibitor, indomethacin, on hypothalamic-pituitary-adrenal function was investigated in five normal males. Baseline 0800 and 1600 h plasma ACTH and cortisol, plasma ACTH and 11-deoxycortisol responses to metyrapone, and plasma cortisol responses to dexamethasone and exogenous ACTH were not affected by indomethacin. However, the area under the curve for plasma ACTH after iv injection of regular insulin (0.1 U/kg) was significantly decreased during indomethacin administration (control, 88.0 +/- 32.6 cm2, mean +/- sd; indomethacin, 47.6 +/- 23.1, P less than 0.01). Plasma cortisol levels were decreased only at 30 min. Our results support the hypothesis that prostaglandins or any of their precursors play a role in the hypothalamic control of ACTH secretion and indicate that evaluation of hypophyseal ACTH secretory capacity by means of insulin-induced hypoglycemia may yield abnormal results in patients receiving indomethacin.

Serum thyrotropin and thyroid hormone levels in humans receiving chronic potassium iodide.

Serum thyroxine (T4), triiodothyronine (T3) and thyrotropin (TSH) concentrations were measured in 13 patients with chronic obstructive pulmonary disease receiving saturated solution of potassium iodide (SSKI). All had a low serum T4 and a high serum TSH concentration. However, serum T3 levels were normal in eight. Recovery of normal thyroid function was observed in each of the seven patients in whom the iodide was discontinued. The same hormones were measured in four normal subjects who received 30 drops of SSKI daily for 11 weeks. An increase in serum TSH levels was preceded by a fall in serum concentrations of T4 and to some extent, T3. Upon SSKI withdrawal subsequent increases in the serum concentrations of both thyroid hormones, but particularly T3, resulted in the return of serum TSH to baseline levels. None of the subjects developed clinical hypothyroidism. It is not apparent why the normal subjects did not exhibit clinical or laboratory evidence of hypothyroidism while the patients with chronic pulmonary disease did. A younger age and the shorter duration of iodide administration in the normal subjects may have played a role.

Hypertension in primary hyperparathyroidism: the role of the renin-angiotensin system.

In four out of seven patients with primary hyperparathyroidism, we have found elevated plasma renin activity (PRA) and blood pressure, both of which returned to normal following surgical correction of the hyperparathyroidism. However, PRA was normal in nonmotensive patients with primary hyperparathyroidism, those with hypercalcemia of other etiologies, and those with secondary hyperparathyroidism. These findings suggest that the renin angiotensin system may play a role in the etiology of the hypertension in primary hyperparathyroidism.

Plasma 1,25-dihydroxyvitamin D levels in patients receiving anticonvulsant drugs.

Recent evidence has linked altered plasma vitamin D metabolite levels to the reported occurrence of hypocalcemia and other metabolic abnormalities in patients receiving anticonvulsant drugs. We have measured plasma levels of 25-hydroxyvitamin D (25-(OH)D) and 1,25-dihydroxyvitamin D (1,25-(OH)2D) in institutionalized patients on diphenylhydantoin (Dilantin) and/or phenobarbital therapy. Values were compared with those obtained in institutionalized patients receiving no drugs and with normal ambulatory subjects. Although plasma 25-(OH)D levels were lower in the patients on drugs, a deficiency of 1,25-(OH)2D, the tissue active metabolite of vitamin D, was not present. These results indicate that in patients taking anticonvulsant drugs, the serum calcium, phosphorus, alkaline phosphatase and parathyroid hormone (PTH) abnormalities are not caused by a defective formation of 1,25-(OH)2D.

Spurious overestimation of plasma cortisol in patients with chronic renal failure.

Plasma cortisol concentrations in patients with chronic renal failure were measured by five different RIAs, four commercial methods, and an in-house method after paper chromatography. It was observed that cortisol concentrations of the same samples measured by the various methods did not agree. The difference was attributed to cross-reactivity of the antisera with steroids and glucuronide conjugates which circulate at high concentrations in patients with chronic renal failure. With two of the methods, values were higher in unextracted plasma (P less than 0.001) than after paper chromatography (in-house procedure). The values obtained with the other two methods were not significantly different from those obtained by the postpaper chromatography method for baseline and postdexamethasone samples. Plasma cortisol values after methyrapone administration were much higher when measured by any of the four commercial assays than after paper chromatography. A simple dichloromethane extraction improved the results from one of the methods. Laboratories are encouraged to assess carefully the behavior of cortisol antisera before using them in the assay of plasma cortisol concentrations in patients with chronic renal failure.

Abnormalities in the regulation of prolactin in patients with chronic renal failure.

We have investigated the hypothalamic-hypophyseal regulation of prolactin secretion in patients with chronic renal failure treated with chronic hemodialysis. When compared to control subjects, baseline serum prolactin levels were elevated in the renal failure patients (range 11 to 16 mmicrogram/ml for renal failure patients, 6 to 9 mmicrogram/ml for controls, P less than 0.05). In addition, serum prolactin levels in the renal failure patients failed to suppress significantly following the administration of L-dopa, and did not increase in response to chlorpromazine or thyrotropin releasing hormone. These findings suggest an abnormal regulation of prolactin secretion and appear to be another example of the endocrine dysfunction that occurs in uremic subjects.

Changes in serum thyroxine, triiodothyronine, and thyrotropin induced by lithium in normal subjects and in rats.

Serum thyroxine (T4), triiodothyronine (T3), and thyrotropin (TSH) were measured in 4 normal subjects before, during, and 2 wk after administration of lithium carbonate (1,200 mg/day) for 6 wk. All subjects developed thyroid enlargement associated with increase in TSH. Serum T3 and T4 did not change significantly. In 3 hypothyroid maintained on thyroxine replacement, lithium administration did not alter circulating levels of T4 or T3, suggesting no effect of lithium on the extrathyroidal metabolism of the thyroid hormones. In rats fed a low iodine diet containing 122 mg/kg/day lithium carbonate, goiter, increased 131I uptake, and a decrease in intrathyroidal T3 and T4 with an increase in MIT, DIT, and MIT/DIT were observed at 3 wk. Serum T3 fell significantly only during the third week, while T4 did not change. Thyroid enlargement, secondary to a rise in TSH, appears to play a role in the adaptation of the thyroid gland to lithium carbonate. The exact mechanism for the elevation of TSH has not been elucidated.

Tissue lipoprotein lipase in the hyperthyroid rat. Effect of growth and aging.

The hydrolysis of lipoprotein triglycerides is catalyzed by lipoprotein lipase (LPL), an enzyme found in many tissues. We have examined tissue LPL activity (LPLA) in rats with experimentally-induced hyperthyroidism. In younger, lighter rats, hyperthyroidism was accompanied by a decrease in LPL in adipose tissue whereas heart and diaphragm muscle LPL activities were increased. These changes are consistent with the hypothesis that the hypercatabolism and increased beta-adrenergic activity of hyperthyroidism result in characteristic changes in tissue LPLA. In older, heavier hyperthyroid animals, however, adipose tissue LPLA was increased and heart and diaphragmatic LPLA were similar to control activities. Propranolol feeding abolished the thyroxine-induced increase in adipose tissue LPLA. In euthyroid animals of similar size the response of muscle LPLA to short-term starvation was also attenuated. These changes in tissue LPLA may provide a mechanism for shunting triglyceride fatty acids away from adipose tissue for utilization by muscle in the hyperthyroid state. During growth and aging, these adaptations are modified.

Osteomalacia associated with anticonvulsant drug therapy in mentally retarded children.

A survey of 289 severely retarded inpatients at a school for retarded children in American Fork; Utah revealed 67 patients with osteomalacia as defined by hypocalcemia, hypophosphatemia, elevated serum alkaline phosphatase levels, and appropriate bone changes. Investigation of the variables which might influence bone mineralization revealed no differences in age, sex, physical activity, sunshine exposure, or dietary intake of vitamin D between the osteomalacia and nonosteomalacia groups. However, all of the patients with osteomalacia were receiving anticonvulsant medications, either phenobarbital, diphenylhydantoin, or both. Duration of anticonvulsant therapy was the most important contributing factor to the development of osteomalacia. Seventy-five percent of patients who had received anticonvulsants for more than ten years had osteomalacia. The single most costly medical problem at the school is the treatment of pathologic bone fractures due to demineralized bone.

Alterations of glucocorticoid actions by other drugs and disease states.

Glucocorticoids are used in physiological and pharmacological amounts in the management of a variety of clinical conditions. Concomitant utilisation of other drugs or the presence of some diseases may affect the physiological action of the steroid in the tissues. Phenytoin, phenobarbitone, ephedrine and rifampicin accelerate the metabolism of glucocorticoids thereby decreasing their biological activity. A similar phenomenon occurs in patients with hyperthyroidism. In contrast, glucocorticoid action is enhanced in hypothyroid patients and in those with hepatic damage as the result of a defect in the clearance of the hormone from blood. In turn, glucocorticoids antagonise the effects of cholinesterase inhibitors and ganglion blocking agents. The above mentioned effects should be kept in mind whenever glucocorticoids are utilised in the diagnosis and management of endocrine or non-endocrine conditions.

1,25-Dihydroxyvitamin D3-induced growth restriction of cultured epithelial cells derived from a murine hepatic tumor.

Recent evidence suggests that 1,25-dihydroxyvitamin D3 can accumulate in certain presumed non-target tissues, although the mechanism of action of the vitamin in such cells is not understood. Exposure of 77-1/3a mouse hepatic tumor cells, which derived from a non-target tissue of vitamin D action, to 1,25-dihydroxyvitamin D3 in chemically-defined serum-free medium resulted in a dose-dependent decline in cellular growth rate and maximal culture population density but did not adversely affect cell viability. Culture of 77-1/3a cells in defined medium containing 10(-7) or 10(-6) M 1,25-dihydroxyvitamin D3 for 150 hr reduced the growth rate to 64 and 50% of control values respectively. Albumin secretion was unaffected by 1,25-dihydroxyvitamin D3 exposure; in contrast, the cellular content of the proliferation-associated protein p35 was reduced by 39%, a decline similar in trend and degree to that observed in other tumor cells exposed to differentiation-inducing agents. It appears that 1,25-dihydroxyvitamin D3 regulates cellular p35 content (within a specific restricted range) as a consequence of proliferative perturbation, rather than differentiated status, of cultured hepatic tumor cells.

Dissociation of E prostaglandin effects on liver glycogenolysis and cyclic AMP levels.

Some metabolic effects of prostaglandins have been related to their alteration of adenosine-3',5'-monophosphate (cyclic AMP) metabolism in different tissues. Prostaglandins E1 and E2 stimulate liver adenylate cyclase in vitro, but conflicting reports have been made about metabolic changes caused by E prostaglandins in hepatic tissue. We have attempted to resolve these issues by comparing the effects of PGE1 with those of glucagon using broken-cell homogenates, intact hepatocytes, liver slices and perfused liver. Prostaglandin E1 (PGE1) increased cyclic AMP in liver slices and in perfused liver without increasing glycogenolysis, but PGE1 had no discernible effect on carbohydrate or cyclic AMP metabolism in isolated hepatocytes. Glucagon caused predictable increases in cyclic AMP and glycogenolysis using hepatocytes, liver slices or perfused liver. These data can be explained by the absence of PGE effects on cyclic AMP metabolism in hepatocytes. The concentration of E prostaglandins (PGEs) increased 1.75-fold during incubations (37 degrees C) of hepatocyte suspensions, but cyclic AMP remained constant. Addition of exogenous arachidonate and indomethacin to cell suspensions increased and decreased PGEs, respectively, but cyclic AMP and glycogen metabolism were unchanged. Arachidonate and indomethacin likewise did not alter glucagon-stimulated glycogenolysis or cyclic AMP biosynthesis. The production of E prostaglandins and cyclic AMP appears to be unrelated in hepatocytes.

Absorption and biotransfomation of cholecalciferol in drug-induced osteomalacia.

The gastrointestinal absorption of vitamin D3 and its biotransformation to 25-hydroxycholecalciferol was studied in patients with drug-induced osteomalacia. The mean coefficient of absorption was virtually identical in the drug-treated group (82.8%) and the control (83.8%). The biotransformation of vitamin D3 to 25-hydroxycholecalciferol was significantly accelerated (P less than 0.03) in the drug-treated group compared to the control group. These data suggest that vitamin D absorption is not significantly altered but that biotransformation of vitamin D3 to 25-hydroxycholecalciferol is accelerated in drug-induced osteomalacia.