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Biomedical subjects

T J Hahn

Publications and source records attributed to T J Hahn.

At least 55 records · Page 3Linked to original sources
PubMed1981

Effects off short term glucocorticoid administration on intestinal calcium absorption and circulating vitamin D metabolite concentrations in man.

These studies were performed to examine the hypothesis that glucocorticoids suppress intestinal calcium absorption in man by decreasing the circulating concentrations of biologically active vitamin D metabolites. Twelve normal adults were equilibrated for 2 weeks on a 600-mg calcium diet. After equilibration, subjects were studied for 12 days before and 14 days during the administration of prednisone (20 mg/day). After 14 days of prednisone administration, intestinal 47Ca absorption had decreased by 31% from initial values (P < 0.001). However, mean serum concentrations of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D did not change significantly from initial values of 28.1 +/- 1.8 and 2.09 +/- 0.17 pg/ml, respectively, and the serum 1,25-dihydroxyvitamin D concentration was slightly increased (baseline, 34.8 +/- 3.3; day 14, 54.0 +/- 7.1 pg/ml; P < 0.02). The fasting serum immunoreactive parathyroid hormone concentration did not change. These results demonstrate that reduced intestinal calcium absorption after glucocorticoid administration cannot be attributed to decreasing circulating concentrations of the major known vitamin D metabolites.

24,25-Dihydroxyvitamin D 3↗
PubMed1980

Ouabain effects on hormonally-stimulated bone resorption and cyclic AMP content in cultured fetal rat bones.

Ouabain in concentrations from 20-100 micromoles produced a dose-related inhibition of in vitro stimulation of bone resorption by parathyroid hormone, 1,25-dihydroxyvitamin D3 and calcium ionophore A23187, as measured by 45Ca and [3H]-hydroxyproline release in 5-day cultures of fetal rat forelimb rudiments. The inhibitory effect on 45Ca release was completely reversed by subsequent incubation in ouabain-free medium. At a concentration of 100 micromoles ouabain virtually abolished active bone resorption; however, basal and stimulated bone cyclic AMP (cAMP) content were significantly increased above levels observed in the absence of ouabain. The increased cAMP content did not appear to be the result of phosphodiesterase inhibition. It is concluded that intact Na/K ATPase function is required for hormonally-stimulated bone resorptive processes and that the inhibitory effect of ouabain on bone resorption is produced at a point subsequent to cyclic AMP generation.

Animals↗
PubMed1979

Cortisol enhancement of PTH-stimulated cyclic AMP accumulation in cultured fetal rat long bone rudiments.

Cortisol in concentrations from 10 nM to 10 microM produced a dose-related inhibition of basal and PTH1-stimulated 45Ca and [3H]-hydroxyproline release from cultured fetal rat forelimb rudiments. PTH-stimulated cyclic AMP generation however was not diminished by cortisol; in contrast, at a concentration of 1 microM cortisol produced a 57% increase in PTH-stimulated bone cyclic AMP content. The stimulatory effect of cortisol on cyclic AMP content appeared to be the result of reduced phosphodiesterase activity, since this effect was not seen in the presence of 10 mM theophylline. It is concluded that cortisol inhibition of PTH-induced resorption in long bones is not accompanied by reduced cyclic AMP generation.

Animals↗
PubMed1979

Disordered mineral metabolism produced by ketogenic diet therapy.

Vitamin D and mineral metabolism status was examined in five children maintained chronically on combined ketogenic diet-anticonvulsant drug therapy (KG), and the results compared to those obtained in 18 patients treated with anticonvulsant drugs alone (AD) and 15 normal controls. KG patients exhibited biochemical findings of vitamin D deficiency osteomalacia: decreased serum 25-hydroxyvitamin D (25OHD) and calcium concentrations, elevated serum alkaline phosphatase and parathyroid hormone concentrations, decreased urinary calcium and increased urinary hydroxyproline excretion, and decreased bone mass. Although the KG and AD groups demonstrated similar reductions in serum 25OHD concentration, the KG patients exhibited a significantly greater reduction in bone mass. In response to vitamin D supplementation (5000 IU/day), mean bone mass in the KG group increased by 8.1 +/- 0.9% (P less than 0.001) over a 12-month period. These results suggest that ketogenic diet and anticonvulsant drug therapy have additive deleterious effects on bone mass and that these effects are partially reversible by vitamin D treatment.

Acidosis↗
PubMed1979

Effect of lithium on parathyroid hormone-induced calcium release from bone rudiments.

Lithium treatment of humans and animals has been associated with adverse effects on bone and mineral metabolism. In order to determine whether lithium was altering the skeletal response to parathyroid hormone, we incubated bone rudiments for 5 days in the presence or absence of the drugs. Lithium had no effect on either parathyroid hormone-induced cyclic AMP generation or 45Ca release from the bone rudiments. The data are consistent with the hypothesis that the skeletal effects of lithium are not mediated via inhibition of the parathyroid hormone-adenyl cyclase-cyclic AMP system.

Animals↗
PubMed1979

Anticonvulsant drug-induced osteomalacia: alterations in mineral metabolism and response to vitamin D3 administration.

Parameters of mineral metabolism were examined in 6 patients with moderately severe anticonvulsant drug-induced osteomalacia. Compared to 15 matched controls, the patients exhibited significantly reduced serum calcium, inorganic phosphate, and 25-hydroxyvitamin D concentration, elevated serum alkaline phosphatase and immunoreactive parathyroid hormone (iPTH) concentration, reduced intestinal 47Ca absorption, reduced urinary calcium and increased urinary hydroxyproline excretion, and reduced forearm bone mass. Intestinal absorption of vitamin D3 was normal. Following 4 months of treatment with vitamin D3 (4000 units/day), serum 25-OHD concentration was increased to 3 times mean normal values and all parameters except serum iPTH, urinary calcium excretion, and forearm bone mass were returned to levels not significantly different from normal. Serum iPTH concentration was reduced by 39% (P less than 0.05); 24-h urinary calcium excretion rose by 98% (P less than 0.001), and forearm bone mass increased by 5.6% (P less than 0.05). It is concluded that moderate-dose vitamin D3 supplementation is effective in normalizing parameters of mineral metabolism in this disorder, despite evidence of resistance to the biologic effects of vitamin D.

Adult↗
PubMed1979

Reduced serum 25-hydroxyvitamin D concentration and disordered mineral metabolism in patients with cystic fibrosis.

Vitamin D and mineral metabolism were studied in 21 adolescents and young adults with cystic fibrosis and the results were compared to those in 21 matched controls. All CF patients had been maintained on standard multivitamin supplements in combination with pancreatic enzyme replacement. Despite this supplementation, relative to control subjects the CF patients had a 36% reduction in serum 25-hydroxyvitamin D concentration, a slight but significant reduction in serum calcium concentration, evidence of calcium malabsorption with secondary hyperparathyroidism, and a 14% decrease in bone mass measured by the photon absorption technique. Currently accepted modes of pancreatic enzyme replacement and vitamin D supplementation are often inadequate to maintain normal mineral homeostasis in CF patients; additional measurements may be required to reduce the risk of clinically significant osteopenia concomitant with prolonged survival in CF.

Adolescent↗
PubMed1979

Altered mineral metabolism in glucocorticoid-induced osteopenia. Effect of 25-hydroxyvitamin D administration.

Parameters of mineral and bone metabolism were studied in 17 patients treated chronically with supraphysiologic doses of glucocorticoids. When compared to 15 matched normal subjects, the patient group exhibited similar serum 25-hydroxyvitamin D (25-OHD) levels, decreased intestinal 47Ca absorption, increased serum immunoreactive parathyroid hormone, and decreased forearm bone mass. Iliac crest bone biopsies revealed a decreased bone formation rate and increased osteoclast number. Treatment with 25-OHD (mean dose 4.03 micrograms/d) and calcium (500 mg/d) in nine patients produced a 46% increase in 47Ca absorption (P less than 0.001) and a 54% decrease in serum immunoreactive parathyroid hormone (P less than 0.001) by 3 mo. In addition, by 12 mo the treatment group exhibited (a) a 13.2 +/- 5.1% increase in metaphyseal (P less than 0.001) and a 2.1 +/- 0.4% increase in diaphyseal (P less than 0.05) forearm bone mass, and (b) significant decreases in cortical and endosteal osteoclast number. Biochemical and bone mass changes persisted through 18 mo. No significant changes in any parameter occurred in eight control patients administered calcium 100 mg/d. It is concluded that treatment with 25-OHD and calcium can significantly improve parameters of mineral and bone metabolism in patients with glucocorticoid-induced osteopenia.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1978

Interaction of diphenylhydantoin (phenytoin) and phenobarbital with hormonal mediation of fetal rat bone resorption in vitro.

Chronic administration of high doses of anticonvulsant drugs frequently produces classic osteomalacia with bone histologic changes characteristic of increased parathyroid hormone (PTH) effect in man. However, several reports have documented defects in calcified tissue metabolism suggestive of an end-organ resistance to PTH after chronic anticonvulsant drug therapy. To examine the direct action of anticonvulsant drugs on bone resorption, we investigated the effects of diphenylhydantoin (phenytoin) (DPH) (100-200 mug/ml) and phenobarbital (10-400 mug/ml) on basal and hormonally mediated resorption 5-day cultures of fetal rat forelimb rudiments. In this system both drugs significantly inhibited basal and PTH-stimulated (45)Ca and [(3)H]hydroxyproline release, as well as 1,25-dihydroxyvitamin D(3)-stimulated (45)Ca release. The effects of DPH and phenobarbital were additive, with DPH exhibiting a several-fold more potent inhibitory effect than phenobarbital. Whereas DPH exhibited a striking synergism with the inhibitory effects of human calcitonin (HCT) on PTH-induced resorption, the effect of phenobarbital was merely additive to that of HCT. PTH and PTH plus HCT-induced increases in bone cyclic AMP (cAMP) content were significantly inhibited by DPH but not by phenobarbital. However, in contrast to effects on (45)Ca release, DPH inhibition of cAMP generation was not accentuated in the presence of HCT. It is concluded that: (a) both DPH and phenobarbital can directly inhibit basal and hormonally stimulated bone resorption, with DPH being much more potent in this regard; (b) DPH appears to inhibit bone resorption via a cAMP-independent mechanism and has an additional suppressive effect on PTH-induced cAMP generation; and (c) the synergistic interaction of DPH and HCT in inhibiting (45)Ca release occurs at a site independent of cAMP generation.

Animals↗
PubMed1978

Effect of oral glucose ingestion on renal phosphate reabsorption and clearance in vitamin D-resistant rickets.

The effect or oral glucose ingestion on renal phosphate reabsorption was studied in 13 patients with the inherited form of vitamin D-resistant rickets (VDRR) and 5 normal subjects. In contrast to the normal subjects, glycosuria developed in six VDRR patients after glucose ingestion and resulted in a further 43% decrease in renal phosphate reabsorption. This was accompanied by a 33% increase in phosphate clearance. This was not attended by differences in fasting glucose or phosphorus levels between groups, or in their respective values 1 h after glucose ingestion. Baseline renal phosphate reabsorption was less and baseline phosphate clearance was greater in those VDRR subjects who developed glycosuria. The accumulated data suggest that excessive glucose ingestion by some patients with VDRR may add an additional insult to the phosphaturia characteristic of this disorder. This, in turn, would further compromise the response of circulating phosphate to therapeutic attempts at oral phosphate supplementation, thereby reducing the efficacy of oral phosphate therapy on skeletal growth and development in this disorder.

Adolescent↗
PubMed1978

ACTH-secreting medullary carcinoma of the thyroid presenting a severe idiopathic osteoporosis and senile purpura: report of a case and review of the literature.

A 64-yr-old female presented with severe osteoporosis and easy bruisability of over 2-yr duration. Biopsy of a neck mass revealed medullary carcinoma of the thyroid. Subsequently, lymphangitic pulmonary metastases were demonstrated which had been present radiographically for at least 4 yr. Basal serum calcitonin was markedly elevated and increased during calcium infusion. The diagnosis of ectopic ACTH syndrome was first entertained when hypokalemic alkalosis was observed during evaluation of her carcinoma. Elevated urinary 17-hydroxycorticosteroids, 17-ketosteroids, plasma cortisol, and immunoreactive plasma ACTH levels were documented. Adrenal steroidogenesis seemed to suppress on high dose dexamethasone. The primary tumor and its metastases contained high concentrations of immunoreactive ACTH and beta-melanocyte-stimulating hormone. Hepatic metastases contained extremely high concentrations of calcitonin. In contrast to the usual presentation of the ectopic ACTH syndrome as primarily hypokalemic alkalosis and glucose intolerance, patients with relatively benign and indolent ACTH-secreting tumors, such as certain cases of medullary carcinoma of the thyroid, may present with more typical signs and symptoms of Cushing's syndrome. The more pronounced cushingoid features in this latter group presumably reflects a more prolonged period of exposure to elevated glucocorticoid levels. Ten cases of ACTH-secreting medullary carcinoma of the thyroid from the literature are discussed. Extopic ACTH production by such tumors should be considered in the evaluation of patients with Cushing's syndrome or unexplained severe osteopenia.

Adrenocorticotropic Hormone↗
PubMed1977

Serum 25-hydroxyvitamin D concentrations in patients receiving chronic corticosteroid therapy.

Serum 25-hydroxyvitamin D (25OHD) concentrations were measured by competitive protein-binding assay in 21 patients who were receiving chronic prednisone therapy and who demonstrated radiologic osteopenia. Results were compared to values obtained in 19 matched non-steroid-treated control subjects. Serum 25OHD values in control and steroid-treated subjects were virtually identical and showed a similar positive correlation with vitamin D intake. To rule out possible assay interference by postulated steroid-induced abnormal vitamin D metabolites, 25OHD was specifically isolated from pooled extracts of control and steroid-treatment patient sera by silicic acid column chromatography. 25OHD levels were again identical in both groups, and there was no evidence of radioassayable abnormal metabolites. It is concluded that the maintenance of normal serum levels of 25OHD is not altered by chronic moderate dose corticosteroid therapy.

Adrenal Cortex Hormones↗