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Studies were carried out to characterize the secretion and the effects of calcitonin in the Buffalo rat. Mean basal concentrations of calcitonin and parathyroid hormone were significantly increased in serum of rats older than 6 months of age as compared with rats between 2 and 3 months of age. The mean concentration of calcium in serum was independent of age. In both age groups, serum calcitonin was increased by administration of calcium (1 mmol/kg body wt) or isoproterenol (100 microgram/kg body wt), was diminished by beta-adrenergic blockade with DL-propranolol (1 mg/kg body wt) and was not altered by either pentagastrin or glucagon (200 and 100 microgram/kg body wt respectively). The average weight of the thyroid glands was significantly greater in the old than in the young animals but the mean concentration of calcitonin in the thyroids was the same. Thyroparathyroidectomy produced a transient increase followed by a fall in mean serum calcium in the old rats. In contrast, a progressive decline in the mean concentration of calcium in serum was observed after thyroparathyroidectomy in the young rats. Treatment of old animals with reserpine (2.5 mg/kg body wt) markedly depleted noradrenaline in the thyroid, lowered calcitonin in serum and converted the pattern of response of serum calcium to thyroparathyroidectomy to that observed in young animals. The results provide evidence that hypercalcitonaemia occurs in aged Buffalo rats, as does hyperparathyroidism, and that the concentrations of calcitonin in blood are modulated by beta-adrenergic affectors. Glucagon and pentagastrin exhibit little if any effects on calcitonin secretion in this strain of rat regardless of age.

It is known that the secretion of PTH is often impaired in association with aluminum (Al3+) accumulation in patients with renal failure. The mechanisms involved remain ill defined. Since adenylate cyclase plays a role in the regulation of PTH secretion, these studies examine the effects of Al3+ on parathyroid adenylate cyclase. In membranes from normal bovine parathyroid glands, basal adenylate cyclase activity, in the presence of 0.2 mM ATP and 20 mM Mg2+, increased by 22% as Al3+ was raised from 0-10 microM. Higher Al3+ concentrations caused a progressive decrease in adenylate cyclase activity, reaching 68% inhibition of control activity at 2 mM Al3+. Since adenylate cyclase activation is influenced by the interaction of multiple sites within the adenylate cyclase complex, the nature of the inhibition by Al3+ was explored by examining the interaction of Al3+ with substrate ATP and with Mg2+, an allosteric activating metal ion. In the presence of 20 mM Mg2+, Al3+ concentrations of 1-2 mM resulted in noncompetitive inhibition with respect to ATP [decrease in maximum velocity (Vmax) from 4176 in the absence of Al3+ to 1106 pmol cAMP/mg protein X 15 min; Michaelis Menten constant (Km) for ATP was unchanged]. In contrast, at fixed ATP (0.2 mM), 0.5 mM resulted in competitive inhibition of adenylate cyclase with respect to Mg2+, whereas at higher Al3+ concentrations the inhibition was noncompetitive. When Mg2+ was replaced by Mn2+ (enzyme activity reflects the activity of the catalytic unit), the inhibitory effect of Al3+ on adenylate cyclase activity was abolished. These data suggest that the inhibition of parathyroid adenylate cyclase by Al3+ occurs at the level of the allosteric metal activating site. These data provide a potential mechanism for the inhibition of PTH secretion by Al3+.

We have examined the changes in bone histology in 28 uremic patients after long-term treatment with the aluminum chelator, deferoxamine. Marked declines in stainable bone-surface aluminum were associated with increases in bone formation rate and osteoblastic osteoid following deferoxamine. The increased bone formation resulted from increases in bone apposition and length of double-tetracycline labels, the latter being highly correlated with the increase in osteoblastic osteoid (r = 0.85). While bone surface aluminum was highly correlated with bone formation rate (r = .69, p less than .001), bone aluminum content did not correlate with bone formation (r = 0.13) and was often elevated after treatment despite an improvement in bone histology. Patients who had undergone prior parathyroidectomy were less likely to have improved bone histology than those with intact parathyroid glands. We conclude that aluminum chelation therapy with deferoxamine is effective in ameliorating the bone histology of patients with chronic renal failure and bone aluminum accumulation, and that the change in stainable bone-surface aluminum is a more sensitive indicator than the change in bone aluminum content in assessing adequacy of chelation therapy. Patients who need deferoxamine treatment but have undergone a prior parathyroidectomy will probably require a more intensive treatment schedule than those who have intact parathyroid glands.

The role of 24,25(OH)2D3 on parathyroid gland function remains controversial. The present studies were performed in vitro using (a) dispersed normal bovine parathyroid cells (bPTC) and (b) dispersed canine PTC (cPTC) prepared from glands of normal dogs, dogs with chronic renal failure (CRF), and dogs with CRF treated with 24,25(OH)2D3, 2.5 micrograms orally every day for more than 6 months. Bovine parathyroid cells were incubated for up to 180 min at 0.5, 1.0, and 3.0 mM external calcium in the presence or absence of 24,25(OH)2D3 (100 or 1000 nM). Similar experiments were conducted with cells incubated for 24 h in the presence of either the ethanol vehicle or 24,25(OH)2D3 (1000 nM). Parathyroid hormone secretion, measured in the supernatant by both C-terminal and N-terminal assays, did not show any differences between control and experimental groups at any time interval. Canine parathyroid cells obtained from uremic animals showed an average threefold increase in the total amount of PTH secreted, on a per cell basis over 180 min at 0.5 mM Ca2+, when compared with normal controls. However, there was no significant difference in PTH secretion at any level of calcium concentration between the cells obtained from parathyroid glands of CRF dogs and 24,25(OH)2D3-treated CRF dogs. Acute exposure to 24,25(OH)2D3 (1000 nM) in vitro of the cells obtained from the glands of CRF dogs also had no effect on PTH secretion. We conclude that 24,25(OH)2D3 has no direct effect on PTH secretion from dispersed parathyroid cells of either normal or uremic animals.

Experiments were performed on a particulate fraction from human parathyroid glands. A high activity of adenylate cyclase was detected which was linear with time and protein concentration. The enzyme had an optimum pH in the range of 7-8 and a Km for ATP of 0.44 X 10(-3) M. Ca++ had a profound inhibitory effect; a concentration of 0.5 mM Ca++ reduced enzyme activity by 60%. Maximal enzyme activity was obtained with 5 mM Mg++; higher concentrations of this cation also inhibited enzyme activity. The effect of Mn++ was similar to that of Mg++. Enzyme activity was stimulated by NaF, catecholamines, glucagon, and calcitonin. The effect of catecholamines seems to be mediated through beta-adrenergic receptors.

Of 100 consecutive patients with recurrent renal calculi, 43 had idiopathic hypercalciuria (IH) on outpatient evaluation. Hypercalciuria was classified as diet-dependent or fasting; all patients had normal serum iPTH and urinary cyclic AMP, and serum phosphate and TmPO4/GFR were reduced in IH compared to normocalciuric stone formers. In 16 patients with IH, clearance studies revealed an elevated urine flow are factored for GFR (V/GFR) as compared with normal controls (p less than 0.05). In 12 patients, serum PTH was normally suppressed by calcium infusion but TmPO4/GFR was persistently reduced. Acute and chronic phosphate administration significantly reduced urine calcium excretion but did not correct the abnormal V/GFR. We conclude that in IH of both the fasting and the diet-dependent type, there is a defect in the proximal tubular reabsorption of sodium and fluid as well as PTH-independent tubular phosphate wasting. The proximal tubular defect is not a consequence of hypercalciuria nor of phosphate depletion but may be a cause of these abnormalities.

Because of differing reports of an effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on parathyroid hormone (PTH) secretion, the present studies were performed in vitro using bovine parathyroid gland slices and isolated parathyroid cells. Both COOH-terminal and NH2-terminal RIAs for PTH were employed. No effect of 1,25(OH)2D3 on PTH secretion was found during a 4-h incubation of parathyroid slices in variable external calcium concentrations. The results from dual RIA measurements also showed no effect of 1,25(OH)2D3 on PTH secretion by isolated parathyroid cells during 90- to 150-min incubations with variable calcium concentrations. In addition, extensive analysis by polyacrylamide gel electrophoresis showed no effect of 1,25(OH)2D3 on cAMP generation. Whereas calcium inhibited and isoproterenol stimulated the production of cAMP, 1,25(OH)2D3 had no effect. We conclude that 1,25(OH)2D3 does not affect parathyroid gland function acutely in vitro.

The histologic features of renal osteodystrophy and the prevalence of bone aluminum deposition in children receiving regular dialysis have not been described. Forty-four pediatric patients undergoing continuous ambulatory (CAPD) or cycling (CCPD) peritoneal dialysis had bone biopsies and deferoxamine (DFO) infusion tests; all were receiving oral calcitriol. Osteitis fibrosa (OF) was found in 39%, mild lesions (M) in 25%, normal histology (NH) in 16%, aplastic lesions (AP) in 11%, and osteomalacia (OM) in 9%. Bone surface aluminum (SA) was present by histochemical staining in 10 out of 20 given aluminum-containing phosphate-binding agents and in 0 of 24 treated with calcium carbonate; chi 2 = 15.5, P less than 0.0001. Serum biochemistries and DFO infusion tests failed to predict bone histology, but plasma aluminum levels were markedly elevated and bone aluminum content was highest in patients with OM. Bone formation rate (BFR) correlated with serum parathyroid hormone (PTH), r = 0.55, P less than 0.001; BFR was inversely related to bone aluminum content (r = -0.42, P less than 0.01), even in patients with OF (r = -0.66, P less than 0.05). All patients with SA greater than 30% had normal or reduced BFR when compared to those with SA less than 30%; chi 2 = 12.2, P less than 0.005. Based on SA greater than 30%, six patients were classified as aluminum-related bone disease: three OM, one AP, and two NH. Two-thirds of pediatric patients undergoing CAPD/CCPD have persistent hyperparathyroidism despite treatment with calcitriol, but aluminum can adversely affect BFR when SA exceeds 30% regardless of histologic lesion or serum PTH level.

The renal degradation of intact bovine parathyroid hormone (b-PTH 1-84) was studied with the isolated perfused dog kidney. Disappearance of b-PTH 1-84 from the perfusate occurred concomitantly with the appearance of smaller molecular weight forms of immunoreactive parathyroid hormone (PTH). These smaller molecular weight PTH fragments included both carboxyl and amino terminal regions of the PTH peptide. Perfusate from kidneys with lower glomerular filtration rates (GFR) contained b-PTH 1-84 for longer periods of time than kidneys with higher GFRs, and perfusate from kidneys with lower GFRs demonstrated greater accumulation of carboxyl terminal PTH fragments. Perfusate containing high Ca++ concentrations retarded, and perfusate with low Ca++ concentrations accelerated the rate of degradation of b-PTH 1-84 by the kidney. These studies, therefore document the production of PTH fragments during the course of intact hormone degradation by the kidney. They also demonstrate renal clearance of the PTH fragments produced and define the effects of glomerular filtration rate and calcium concentrations on degradation of intact hormone and the clearance of PTH fragments.

Controversy exists over a direct effect of 1,25(OH)2D3 on PTH secretion. To investigate the possibility that the suppressive effect of 1,25(OH)2D3 on PTH secretion may be demonstrable in 1,25(OH)2D3-depleted tissue and/or after prolonged periods of exposure to 1,25(OH)2D3, primary monolayer cultures of bovine parathyroid cells were established in 1:1 DMEM/Ham's F-12 media supplemented with 2% calf serum but not 1,25(OH)2D3. Ionized calcium was maintained at 1.0 mM. Experiments were performed on 4-day-old culture cells. PTH concentration was measured using both a mid-region/carboxyl and an amino-terminal PTH antisera. 1,25(OH)2D3 at a concentration of 0.1 ng/ml suppressed PTH secretion by 32 +/- 7% after 48 hours. High calcium concentration (2.0 mM) suppressed PTH secretion by 37 +/- 10% and this effect was not additive over that of 1,25(OH)2D3. PTH secretion rate recovered fully 48 hours after normalization of the external calcium concentration but not after the removal of 1,25(OH)2D3. It is concluded that 1,25(OH)2D3 directly suppresses PTH secretion by monolayer culture of bovine parathyroid cells.

Serum phosphorus concentrations are maintained within narrow limits in humans. In the extracellular fluid most of the phosphorus is present in the inorganic form and at the level of the glomerulus greater than 90% of PO4 is ultrafilterable. The kidney plays a key role in PO4 homeostasis. Micropuncture experiments have demonstrated that 60 to 70% of the filtered PO4 is reabsorbed in the proximal tubule; however, there is evidence that a significant amount of PO4 is reabsorbed in the distal tubule. Phosphate secretion probably plays a minor role in the overall renal regulation of phosphate. In normal individuals the amount of PO4 ingested plays a key role in the amount that ultimately will be excreted in the urine. The reabsorption of PO4 along the nephron is regulated by a series of factors of which parathyroid hormone is the most important one. Hyperphosphatemia is seen frequently in clinical medicine and by far, the most common cause is a decrease in urinary PO4 excretion secondary to renal failure. From the practical point of view, the most effective way to treat hyperphosphatemia is to decrease PO4 absorption in the GI tract by the use of PO4 binders.

Hepatic and renal extraction of immunoreactive parathyroid hormone (i-PTH) was studied in awake dogs with explanted kidneys and chronic indwelling hepatic vein catheters. After a single injection of bovine PTH 1-84 (b-PTH 1-84), hepatic arteriovenous (A-V) differences for immunoreactive PTH (i-PTH) was 39% at 2 min after injection but decreased to 0% by 25 min, despite high levels of i-PTH in the arterial circulation. Gel filtration of arterila and hepatic venous samples obtained when hepatic A-V differences for i-PTH were demonstrable revealed hepatic uptake of the intact hormone and addition of a smaller COOH-terminal fragment, eluting just after the intact hormone, to the hepatic venous blood. Gel filtration of samples obtained 20-30 min after injection of b-PTH was demonstrable) revealed no detectable intact hormone in the circulation. Levels of COOH-terminal fragments of the hormone at the time were identical in arterial and hepatic venous samples. In additional experiemtns no hepatic A-V difference was observed after the injection of the synthetic bovine PTH 1-34 (syn b-PTH 1-34). By comparison there was a demonstrable A-V difference of 20% across the kidney for both intact PTH and COOH-terminal fragments that persisted until i-PTH disappeared from the circulation. The kidney also demonstrated an A-V difference of 22% after injection of syn b-PTH 1-34. These studies demonstrate selective extraction of intact PTH but not of its fragments by the liver. The kidney, on the other hand, extracted the intact hormone and both COOH and NH2 terminal fragments. The studies demonstrate that the kidney was the only organ of those examined that detectably removed the fragments of PTH from the circulation.

Although it is well known that aluminum (Al) plays a role in the development of osteomalacia in patients with chronic renal failure, the mechanisms are not fully understood. Since the osteoblasts are the cells responsible for the formation of osteoid tissue, which is greatly affected in patients with Al-induced osteomalacia, it is possible that Al could affect the number of osteoblasts or interfere with their function. To further characterize this potential mechanism, we performed studies in isolated perfused tibiae from normal and Al-treated dogs. In this system, when PTH is added to the perfusate, cAMP, a major marker of osteoblasts, is released. The dogs were divided into two groups: control, and Al-treated (0.75 mg/kg, iv, 5 days a week for 3 months). Thereafter, the dogs were killed, and the tibiae were perfused in vitro. PTH-(1-34) (3-4 ng/ml) and 3-isobutyl-1-methylxanthine (an inhibitor of phosphodiesterase) were added to the perfusate. Basal cAMP secretion was the same in both groups of dogs. After PTH was added to the perfusate, cAMP increased to a peak of 188.2 +/- 30.6 pmol/min in the normal dogs vs. 113 +/- 8.15 in Al-treated dogs (P less than 0.05). Cumulative cAMP secretion over a 30-min period was 766 +/- 127.9 pmol in the normal dogs vs. 455.6 +/- 38.2 pmol in the experimental animals (P less than 0.05). The histological appearance of bone biopsies taken before and after Al administration are consistent with a suppressive effect of the cation on osteoblast function. In particular, the number of osteoblasts had decreased 8-fold (P less than 0.01) under the influence of Al, and tetracycline-based measurements of mineralization kinetics show that osteoblast-mediated calcification was dysfunctional (P less than 0.01-0.025). On the other hand, the histological features of the post Al treatment biopsies suggest that at some time during its administration, the cation stimulates osteoblastic activity. For example, new (woven) bone formation was present in two dogs, and in another, lamellar bone, deposited under the influence of Al, covered the entire trabecular surface. Moreover, Al-associated osteoid was deposited independent of prior resorptive activity, indicating that the cation promotes bone formation in the absence of prior resorption. In keeping with its trophic effect on matrix deposition, Al also led to extensive marrow fibrosis in five dogs, indicating that Al also stimulates the activity of fibroblasts, cells closely related to osteoblasts.(ABSTRACT TRUNCATED AT 400 WORDS)

The interaction between glucocorticoids (GC) and PTH has been suggested to play a role in the pathogenesis of GC-induced osteopenia. The present studies were designed to examine the effect of acute (5-h) or chronic (4-week) GC administration in vivo on 1) cAMP release by the isolated perfused dog tibia before (basal) and after the addition of synthetic bovine PTH-(1-34) [syn bPTH-(1-34)] (stimulated) to the perfusate in vitro, in the presence or absence of the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (IBMX; 1 mM), and 2) the percent arteriovenous difference of immunoreactive PTH across bone. Acute administration of 6 mg/kg methylprednisolone (MP) did not affect the basal release of cAMP from bone (6.9 +/- 1.6 pmol/min in control vs. 6.1 +/- 1.2 pmol/min in MP-treated animals); however, syn bPTH-(1-34) stimulated release of cAMP was higher in the MP-treated animals (45 +/- 8.1 pmol/min) than in controls (26.8 +/- 3.0 pmol/min). When IBMX was added to the perfusate, basal cAMP release was not different in control and MP-treated bone (17.2 +/- 2.1 pmol/min in control vs. 19.1 +/- 1.9 pmol/min in MP-treated bone), and syn bPTH-(1-34)-stimulated release of cAMP was equivalent in both groups. In contrast, chronic prednisone therapy lead to a decrease in both basal and PTH-stimulated release of cAMP from bone (3.1 +/- 0.4 and 6.9 +/- 1.6 pmol/min for basal, and 13.1 +/- 1.7 and 26.8 +/- 3.0 pmol/min for stimulated values, respectively). However, the percent changes from the basal levels were not different in the two groups. These results were correlated with histological studies of rib biopsies obtained from these animals, which showed evidence of osteopenia and decreased bone turnover. Neither acute nor chronic GC administration had any effect on arterio-venous differences for PTH across the bone. Thus, these studies demonstrate that 1) acute administration of MP enhances the response of bone to PTH, an effect that is not apparent in the presence of the phosphodiesterase inhibitor IBMX; and 2) chronic prednisone therapy decreased basal and PTH-stimulated cAMP release, an effect that correlated with histological evidence of decreased bone turnover.

Study Objective: To assess the effect of weight-bearing exercise training and subsequent detraining on lumbar bone mineral content in postmenopausal women., Design: Non-randomized, controlled, short-term (9 months) trial and long-term (22 months) exercise training and detraining (13 months)., Setting: Section of applied physiology at a university school of medicine., Patients: Thirty-five healthy, sedentary postmenopausal women, 55 to 70 years old. All women completed the study. There was 90% compliance with exercise training., Interventions: All women were given calcium, 1500 mg daily. The exercise group did weight-bearing exercise (walking, jogging, stair climbing) at 70% to 90% of maximal oxygen uptake capacity for 50 to 60 min, 3 times weekly., Measurements and Main Results: Bone mineral content increased 5.2% (95% confidence interval [CI], 2.0% to 8.4%; P = 0.0037) above baseline after short-term training whereas there was no change (-1.4%) in the control group. After 22 months of exercise, bone mineral content was 6.1% (95% CI, 3.9% to 8.3% above baseline; P = 0.0001) in the long-term training group. After 13 months of decreased activity, bone mass was 1.1% above baseline in the detraining group., Conclusions: Weight-bearing exercise led to significant increases above baseline in bone mineral content which were maintained with continued training in older, postmenopausal women. With reduced weight-bearing exercise, bone mass reverted to baseline levels. Further studies are needed to determine the threshold exercise prescription that will produce significant increases in bone mass.

In the present investigation, sodium fluoride (NaF) was employed to explore the role of guanine nucleotide-binding proteins (G-proteins), protein kinase-C, or cytosolic calcium [( Ca]i) in the regulation of cytosolic pH [( pH]i) in dispersed bovine parathyroid cells, using the pH-sensitive fluorescent dye BCECF. When cells acidified by nigericin in Na-free medium were resuspended in Na-containing buffer, [pH]i returned to basal levels. This recovery was blocked by continued removal of Na+ or the addition of amiloride. NaF (10 mM) increased [32P]phosphate incorporation into phosphatidylinositol bisphosphate, suggesting an increase in phosphatidylinositol bisphosphate turnover. NaF caused an initial acidification, followed by an alkaline recovery in a dose-dependent manner (1-10 mM). Amiloride blocked the NaF-induced alkaline recovery. The protein kinase-C activator phorbol 12-myristate 13-acetate (10(-7) M) caused cytosolic alkalinization, while the protein kinase-C inhibitor H7 (6 x 10(-5) M) significantly inhibited the NaF-induced alkaline recovery. Pertussis toxin (1 microgram/ml) did not affect the NaF-induced changes in [pH]i. Removal of extracellular Ca2+ with EGTA blocked the NaF-induced increase in [Ca]i and alkaline recovery. Ionomycin (5 x 10(-7) M) caused cytosolic alkalinization, but pretreatment with EGTA inhibited the ionomycin-induced cytosolic alkalinization. The present studies clearly demonstrated the presence of an amiloride-sensitive Na+/H+ exchanger in parathyroid cells. Our findings suggest that the NaF-induced cytosolic alkaline recovery was via two complementing pathways: 1) activation of protein kinase-C, followed by stimulation of a Na+/H+ exchanger, and 2) existence of extracellular calcium and/or an increase in [Ca]i.

These studies examine the release of 3',5'-cyclic adenosine monophosphate (cyclic AMP) from isolated perfused canine bones in response to synthetic bovine parathyroid hormone (syn b-PTH 1-34) and human calcitonin (hCT). Bones for perfusion were obtained from three groups of dogs: control (n = 11); thyroparathyroidectomized (n = 7), and mithramycin-treated thyroparathyroidectomized animals (n = 5). The results indicate that PTH causes a greater release of cyclic AMP from adult bones than CT; the addition of the two hormones simultaneously results in a synergistic rather than an additive effect; mithramycin inhibits the cyclic AMP response to calcitonin; and thyroparathyroidectomy decreases the cyclic AMP release in response to CT stimulation, suggesting that the cells (osteoclast-like) that respond to CT have an impaired response in the absence of PTH; acute TPTX does not affect the response of the cell populations of adult bones to PTH.

There is evidence that 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] affects phospholipid metabolism of intestine, kidney, and bone. There are no such studies concerning the parathyroid gland, which is also a target tissue for 1,25-(OH)2D3. In this investigation we examined the effect of 1,25-(OH)2D3 on the incorporation of radiolabeled choline, inositol, serine, and ethanolamine into the phospholipids of cultured bovine parathyroid cells. Treatment with 10(-8) M 1,25-(OH)2D3 for 48 h caused a significant decrease in [14C]choline incorporation, although there were no differences in the incorporation of radiolabeled inositol, serine, or ethanolamine. Time-course and dose-response evaluations of the 1,25-(OH)2D3 effect revealed that the decrease in [14C]choline incorporation was seen within 12 h of incubation and occurred with as little as 10(-9) M, respectively. In contrast, neither 10(-7) M 25-hydroxyvitamin D3 nor 10(-7) M 24,25-(OH)2D3 caused significant changes in [14C]choline incorporation. When 5 X 10(-6) M cycloheximide was added to the medium, the inhibitory effect of 1,25-(OH)2D3 on [14C]choline incorporation was completely abolished. A significant decrease in phosphatidylcholine content was observed after treatment with 10(-8) M 1,25-(OH)2D3 for 96 h. 1,25-(OH)2D3 did not cause a dramatic change in the fatty acid composition of the phosphatidylcholine. The present studies demonstrate that in parathyroid cells 1,25-(OH)2D3 causes a decrease in [14C]choline incorporation, which could be due to a decrease in the synthesis of phosphatidylcholine or increased degradation. This effect is specific for 1,25-(OH)2D3 and requires new protein synthesis.

The present studies investigate the effects of glucocorticoids on the function of the parathyroid glands using primary cultures of bovine parathyroid cells. Treatment of parathyroid cell cultures with dexamethasone for 48 h caused a dose-dependent stimulation of PTH secretion. The minimal concentration of dexamethasone required for a significant stimulation of PTH secretion was 0.1 nM. The stimulatory effect of dexamethasone on the secretion of PTH was found within 12 h of treatment with 100 nM dexamethasone. The steroids deoxycorticosterone and cortexolone, which do not have glucocorticoid activity were without effect of PTH secretion. Since glucocorticoids may modulate the effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] in other tissues, additional studies were performed to evaluate the interactions of glucocorticoids and 1,25-(OH)2D3. Addition of 1,25-(OH)2D3 to parathyroid cell cultures for 48 h significantly suppressed PTH secretion. In the presence of dexamethasone, however, 1,25-(OH)2D3 also significantly decreased PTH secretion, although it did not reduce PTH secretion to control levels. The treatment of parathyroid cell cultures with 100 nM dexamethasone did not affect the parathyroid cell content of 1,25-(OH)2D3 receptors. In summary, these studies indicate that glucocorticoids significantly increase the secretion of PTH in vitro. This stimulatory effect can be inhibited by 1,25-(OH)2D3. The parathyroid gland is an additional site of physiological antagonism of glucocorticoids and 1,25-(OH)2D3.

Hyperphosphatemia leads to the development of osteitis fibrosa in patients with chronic renal failure. In contrast, crippling osteomalacia may appear in uremic patients who are hypophosphatemic or aluminum intoxicated or who undergo total or subtotal parathyroidectomy. Thus, strict phosphorus control by use of aluminum-containing gels may ameliorate renal osteitis fibrosa, but may potentiate the development of osteomalacia. To evaluate this possibility, we compared the bone histologies of 10 chronic renal hemodialysis patients who consistently maintained predialysis phosphorus levels between 4-5 mg/dl (Strict-P) to those of 46 randomly selected dialysis patients (Random-P). We found that the Strict-P group had lower circulating immunoreactive PTH (P less than 0.02) and alkaline phosphatase (P less than 0.05) levels and, as expected, less evidence of hyperparathyroid bone disease. On the other hand, the Strict-P patients had osteomalacia, as evidenced by moderate osteoid accumulation and reduced capacity of bone to assume a fluorescent tetracycline label. Furthermore, all Strict-P patients had histological evidence of bone aluminum accumulation. We conclude that maintenance of normal serum P levels with aluminum-containing gels in hemodialysis patients prevents severe hyperparathyroid bone disease. Such treatment, however, is also attended by a moderate degree of aluminum-associated osteomalacia.

Profound hypercalcemia can impose both diagnostic and therapeutic difficulties. First, profound hypercalcemia can be life-threatening as well as difficult to control. Second, the use of mithramycin in the treatment of severe hypercalcemia is emphasized. Third, hypercalcemia of hyperparathyroidism cannot be absolutely distinguished from that of malignancy. In the present case, the tubular reabsorption of phosphate, serum calcium levels, and measurement of immunoreactive parathyroid hormone (iPTH) suggested primary hyperparathyroidism, yet ectopic iPTH from a cervical carcinoma was the probable cause of the hypercalcemia.

We have previously demonstrated that while both normal humans and dogs tightly control serum calcitriol levels after 25(OH)D administration, anephric humans and 5/6 nephrectomized dogs significantly increase circulating 1,25(OH)2D when supraphysiological concentrations of 25(OH)D are reached in serum. Plasma 1,25(OH)2D level is determined not only by its rate of production but also by its rate of degradation. To further characterize the mechanisms involved in the responses to 25(OH)D therapy in normal circumstances and in chronic uremia, we measured metabolic clearance rate (MCR) and production rate (PR) of 1,25(OH)2D in normal dogs and in dogs with moderate and severe renal failure, at normal and supraphysiological serum concentrations of 25(OH)D. Basal MCR in uremic dogs, either with moderate or with severe renal failure, did not differ significantly from normals (6.7 +/- 0.7, 6.8 +/- 0.4 and 6.8 +/- 0.3 ml/min, respectively). Oral 25(OH)D administration for two weeks did not affect MCR either in normal animals or in both groups of uremic dogs. 25(OH)D treatment did not affect production rates in normal dogs and in animals with moderate renal failure (with normal basal values of 1,25(OH)2D), but significantly increased 1,25(OH)2D production from 0.13 +/- 0.01 to 0.25 +/- 0.04 micrograms/day (P less than 0.05) in dogs with severe renal insufficiency. These data suggest that it is the basal level of 1,25(OH)2D which regulates the synthesis of 1,25(OH)2D in response to 25(OH)D administration in normal and uremic animals.

Previous studies from our laboratory have characterized the peripheral metabolism of parathyroid hormone (PTH) in the dog using radioimmunoassay techniques following injection or infusion of biologically active, bovine PTH preparations. Other investigators have used biologically-inactive labelled PTH and interpreted their results as representative of the normal physiological processes. Since oxidized inactive PTH does not bind to PTH receptors and since we have found substantial differences between the tissue uptake of active and inactive PTH preparations, it is possible that results obtained with inactive PTH preparations may not totally represent the normal metabolism of PTH. Therefore, we performed studies in rats to compare the disappearance of immunoreactive PTH (i-PTH) from plasma following injection of active or inactive syn b-PTH 1-34. The maneuvers of bilateral ureteral ligation and bilateral nephrectomy were utilized to characterize the sites of tissue uptake of i-PTH. The results obtained indicate that inactive syn b-PTH 1-34 has a significantly slower disappearance from plasma than biologically active syn b-PTH 1-34. Reduction of glomerular filtration by acute bilateral ureteral ligation decreased the disappearance of oxidized PTH more than active PTH. Thus, the results indicate a major dependence on glomerular filtration for the removal of inactive syn b-PTH 1-34. The demonstration that the peripheral metabolism of active and inactive syn b-PTH 1-34 is not identical suggests that studies of the metabolism of inactive PTH preparations do not accurately reflect that of biologically active PTH.

Current evidence suggests that parathyroid gland adenylate cyclase is involved in the control of parathyroid hormone (PTH) secretion. Thus, the altered control of PTH release in hyperparathyroidism may relate to altered adenylate cyclase activation. Therefore, we examined adenylate cyclase kinetics in membrane preparations from hyperfunctioning human parathyroid glands and normal human and bovine parathyroid tissues. There were no differences in the affinity for ATP between enzymes of normal and pathological tissue. However, the enzyme in 10 hyperfunctioning glands showed increased affinity for Mg++. The activation constant for Mg++ (KaMg) of adenylate cyclase in normal human glands was 10.6 +/- 2 mM, a value not different from that of normal bovine parathyroid tissue (9.5 +/- 1 mM). In contrast, the adenylate cyclase in membrane preparations from three of four hyperplastic and six of seven adenomatous human glands showed a markedly reduced KaMg, ranging from 0.85-1.64 mM and from 1.58-6.46 mM, respectively. In one adenoma and one hyperplastic gland, the Ka of the enzyme for Mg++ was close to normal. The addition of guanylylimidodiphosphate or GTP to the incubation mixture increased, in a dose-dependent manner, the apparent KaMg of the enzyme in the abnormal tissue toward normal, suggesting a defective nucleotide regulatory site in the adenylate cyclase of hyperparathyroid glands. In addition, the hyperparathyroid gland enzyme was less susceptible to inhibition by calcium, requiring 0.7-1 mM Ca++ for 50% inhibition, whereas comparable inhibition of the normal adenylate cyclase was seen at 0.22-0.28 mM Ca++. We conclude that the abnormal control of PTH secretion in hyperparathyroidism may be related, at least in part, to alterations in the characteristics of parathyroid gland adenylate cyclase.

Patients with the nephrotic syndrome and normal renal function have low levels of 25(OH)D in serum presumably due to the loss of this metabolite in the urine. Osteomalacia and hyperparathyroidism have been recently reported to occur as a consequence of those low levels of 25-hydroxyvitamin D (25OHD). We studied six patients (aged 26-52 yr) with the nephrotic syndrome (mean duration, 6.7 yr; range, 2-12 yr) and normal renal function, and evaluated their calcium, phosphorus, PTH, and vitamin D metabolite levels. Bone biopsies were obtained in all patients. The creatinine clearance ranged from 83-134 ml/min . 1.73 m2 of body surface, serum albumin was 2.65 +/- 0.42 (+/- SD) g/100 ml, and proteinuria ranged from 3.5-13.2 g/24 h. All patients had normal serum magnesium, phosphorus, ionized calcium, and alkaline phosphatase (total and bone fraction), and normal roentgenographic metabolic bone survey. Serum PTH, measured by the carboxy-terminal RIA, was 5.1 +/- 2.3 mu leq/ml (normal, 2-10), serum 250HD was 8.8 +/- 4.0 ng/ml (normal, 15-30), and 1,25-dihydroxyvitamin D3 was 38 +/- 25 pg/ml (normal, 17-58). Serum vitamin D-binding protein was 420 +/- 42 micrograms/ml (normal, 400-800). The histological appearance of bone biopsies obtained in these patients was not different from that in a group of sex- and age-matched controls. Specifically, there was no increase in the volume of osteoid (unmineralized bone), the percentage of trabecular surface covered by osteoid, or the number of osteoclasts. The cellular rate of mineralization was normal in all six patients. Thus, these data indicate that low serum levels of 250HD in patients with the nephrotic syndrome and normal renal function do not necessarily result in the development of osteomalacia and/or hyperparathyroidism.

Aluminum-induced osteomalacia is a frequent complication observed in patients on maintenance hemodialysis. However, it is not known whether there are direct effects of aluminum on osteoblasts, or alternatively, whether the observed changes are due to changes in PTH or other factors. We sought to determine the effect of micromolar levels of aluminum on osteoblasts using a well-defined cell line derived from a 32P induced osteosarcoma of rat, UMR 106-01, which is alkaline-phosphatase positive, responds to PTH, and synthesizes type I collagen. Aluminum exposure was controlled using tissue culture media with [Al ] less than 1 microgram/liter (40 nM), produced by precipitation of aluminum salts at pH 8.5. The effect of defined [Al ], from 20 to 800 micrograms/liter (0.7 to 30 microM), was then determined by adding back aluminum while measuring DNA and protein synthesis. We found that aluminum depressed DNA synthesis, as determined by 3H-thymidine incorporation, by 60%, with half maximal effect at 20 micrograms/liter (740 nM) in cells at a density of 20,000/cm2. Alternatively, protein synthesis, as determined by 3H-leucine incorporation, did not decline, and in some cases increased. However, qualitative analysis of matrix proteins produced with and without 800 micrograms/liter (30 mM) [Al ] showed no differences. Direct measurements of cell number and protein synthesis confirmed these findings. Al does not alter the PTH-induced cAMP response of these cells. Thus, aluminum has a direct effect on cell division, and probably on protein synthesis, in this osteoblast-like cell line. These effects occur at levels of aluminum below those commonly contaminating tissue culture media, and thus are seen reproducibly only in media of defined [Al ].(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium absorption was measured in eight uremic patients before and after eight days of treatment with 100 or 500 mug of 25-hydroxycholecalciferol (25(OH)D3) per day. Fractional calcium absorption was estimated by administering 47Ca i.v. and orally on separate days and counting forearm radioactivity four hours later. Calcium absorption in four patients with residual renal function rose from 16.3 +/- 2.5 to 40.8 +/- 5.5% after treatment. In order to determine if the increased calcium absorption was mediated by an increase in the production of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) by virtue of increased substrate delivery to the 25-hydroxycholecalciferol-1-hydroxylase system present in the residual renal tissue, identical studies were performed in four anephric patients. Calcium absorption in these patients averaged 15.7 +/- 2.2% during the control period and rose to 46.0 +/- 11.1% after treatment. Increments in serum calcium after treatment were similar in both groups of patients; the mean concentration rose from 9.6 +/- 0.3 to 11.0 +/- 0.6 mg/100 ml. The results indicate that 25(OH)D3 can improve calcium absorption in the absence of renal tissue suggesting that its conversion to 1,25(OH)2D3 may not be necessary for its effect on the gastrointestinal tract in the uremic patient.

Osteoporosis is a state of reduced skeletal mass characterized by various rates of bone remodeling. Multiple locally elaborated factors have been identified that appear to influence the cellular events in bone remodeling. The possible role(s) of these factors in the pathogenesis of osteoporosis is unknown. One such factor, interleukin 1 (IL-1), is of particular interest, as this protein is known to stimulate bone resorption and perhaps formation. Consequently, we have measured the spontaneous secretion of IL-1 activity by cultured peripheral blood monocytes obtained from 22 osteoporotic patients and 14 age-matched control subjects. Monocytes from osteoporotic patients produced more IL-1 than did monocytes from control subjects. When patients were grouped according to monocyte-produced IL-1 activity, dynamic parameters of bone formation, as judged by quantitative histomorphometric analysis of iliac crest bone biopsies and by circulating levels of bone 4-carboxyglutamic acid protein (BGP)--a marker of bone formation--were higher in subjects with elevated IL-1 activity; whereas, indices of bone resorption and static indices of bone formation were similar in subjects with either high or normal IL-1 activity. IL-1 activity released by peripheral blood monocytes appears to reflect bone formation rate in osteoporotic patients and may be of pathogenetic significance in a subset of individuals with osteoporosis.

Aluminum (Al) may cause both osteomalacia and encephalopathy in dialysis patients. Little is known about the biology of Al. This study examined the initial distribution kinetics of Al and its biological effects after injections of 1 mg/kg/day into dogs for 3 to 5 weeks. Following one intravenous dose, the plasma half-life (x +/- SE) was 276 +/- 51.8 min, with an apparent volume of distribution of 1.30 +/- 0.17 liters or 5.90 +/- 0.30% body wt; 10 to 21% of administered Al was excreted in the urine over 150 min, and the renal contribution to plasma clearance of Al correlated with GFR (r = 0.77, P less than 0.05). The total plasma clearance of Al (4.43 +/- 2.83 ml/min) exceeded the renal contribution to plasma clearance (1.94 +/- 0.36 ml/min) in each dog, and in only two instances did the renal contribution reach 50% of total plasma clearance. Serum calcium rose from 9.4 +/- 0.2 to 11.1 +/- 0.3 mg/dl and immunoreactive parathyroid hormone (iPTH) fell by 27 +/- 4% following one Al injection. With repeated Al injections, serum calcium increased from baseline levels of 10.2 +/- 0.07 mg/dl to 11.1 +/- 0.22 and 11.3 +/- 0.46 mg/dl after 1 and 2 weeks, respectively. Renal function declined in all dogs, and serum creatinine exceeded 3.5 mg/dl in four; over the 5 weeks of study, serum calcium correlated with serum creatinine (r = 0.91, P less than 0.001). Liver, kidney, and spleen showed the highest tissue content of Al, and there was substantial uptake by bone; the parathyroid content of Al was modest.(ABSTRACT TRUNCATED AT 250 WORDS)

The chemoprotective and hypocalcemic agent WR-2721, S-2-(3-aminopropylamino) ethyl-phosphorothioic acid, inhibits parathyroid hormone secretion in vivo and in vitro. We report the first clinical use of WR-2721 in refractory hypercalcemia secondary to parathyroid cancer. After several days of saline diuresis the patient received WR-2721, 740 mg/m2 over 15 minutes, resulting in a fall in serum calcium from 11.76 to 9.06 mg/dL within 24 hours. Serum parathyroid hormone levels decreased from 675 to 140 microLeq/mL 2 hours after the infusion was complete. When hypercalcemia recurred the patient was retreated with differing doses and infusion rates to determine the optimal method of drug administration to provide a satisfactory hypocalcemic response without adverse effects. In this patient, WR-2721 in intravenous boluses of 150 mg/m2 was effective without adverse effects. Using high-pressure liquid chromatography with electrochemical detection, plasma pharmacokinetic studies showed that WR-2721's distribution half-life is 0.55 minutes.

We studied the effect of aluminum injections on bones of rats after intervals of 3, 6, and 9 weeks. To study reversibility, we allowed one group to recover for 3 weeks. Both weanling and adult rats were examined to determine the influence of age. The calcium, phosphate, creatinine, and parathyroid hormone levels were similar in aluminum-treated rats and controls. Aluminum could be seen by histochemical stain after 6 weeks, but at that time the bone was otherwise normal. By 9 weeks the bone formation (as measured by tetracycline labeling) in aluminum-treated rats was severely decreased on trabecular and endosteal surfaces. The periosteal surfaces showed normal formation. After 3 weeks of recovery, the bone formation rate in the young aluminum-treated rats was similar to that in the controls, although the serum and bone aluminum values had not significantly decreased. A higher percentage of aluminum was seen in the cement lines. In the adult rats, the bones had more stainable aluminum, and increased osteoid was noted along trabecular and periosteal surfaces. The doses of aluminum used in these rats greatly exceeded those that cause toxicity in humans; thus these findings may not directly apply to clinical practice. We conclude that aluminum administration can lead to decreased rates of bone formation in the rat, despite normal calcium level and renal function, and without decreased parathyroid hormone levels. The peritoneal route of administration could also have contributed to bone lesions by causing peritonitis, malabsorption, or both. Adult rats showed signs of early osteomalacia.(ABSTRACT TRUNCATED AT 250 WORDS)

Parathyroid suppression by intraperitoneal calcitriol (1,25(OH)2D3) during peritoneal dialysis. The purpose of this study was to determine if parathyroid hormone (PTH) suppression could be achieved by increasing calcium mass transfer (Ca MT) with high dialysate Ca (4 mEq/liter) or via intraperitoneal (i.p.) 1,25(OH)2D3 in patients undergoing continuous ambulatory peritoneal dialysis. Eleven patients were dialyzed for two months with standard Ca dialysate (3.5 mEq/liter) followed by two months with 4.0 mEq/liter Ca, then by three months of i.p. 1,25(OH)2D3. During the latter period, patients were randomized to groups whose dialysate contained either 3.5 mEq/liter or 4.0 mEq/liter Ca. We found that 4.0 mEq/liter Ca dialysate more than doubled Ca MT (37 +/- 17 mg/day to 84 +/- 6 mg/day) leading to a modest fall (P less than 0.05) in PTH levels (84 +/- 5.5% of controls). Ionized calcium levels did not change. With i.p. 1,25(OH)2D3, however, ionized calcium rose significantly (P less than 0.001) leading to a decline in PTH levels to 53.9 +/- 7.9% of control values. Serum 1,25(OH)2D3 levels rose from undetectable to 47.7 +/- 7.2 pg/dl (normal range 20 to 35). These studies indicate that increasing Ca MT using a 4.0 mEq/liter Ca dialysate leads to a small reduction in PTH concentrations. On the other hand, i.p. 1,25(OH)2D3 is well absorbed into the systemic circulation, raises ionized calcium levels, and leads to a marked suppression of PTH. Thus, i.p. 1,25(OH)2D3 may be a simple and effective means to suppress secondary hyperparathyroidism in patients undergoing CAPD.