Serum immunoreactive parathyroid hormone (PTH) is increased in obese as compared with nonobese subjects and declines with weight loss. To

As compared with values in white subjects, bone mass is known to be increased and urinary calcium to be diminished in black individuals. To evaluate the possibility that these changes are associated with alterations in the vitamin Dendocrine system, an investigation was performed in 12 black subjects, 7 men and 5 women, and 14 white subjects, 8 men and 6 women, ranging in age from 20 to 35 yr. All of them were hospitalized on a metabolic ward and were given a constant daily diet containing 400 mg of calcium, 900 mg of phosphorus, and 110 meq of sodium. Whereas mean serum calcium, ionized calcium, and phosphate were the same in the two groups, mean serum immunoreactive parathyroid hormone (350±34 vs. 225±26 pg/ml, P < 0.01) and mean serum 1,25-dihydroxyvitamin D (1,25(OH)2D) (41±3 vs. 29±2 pg/ml, P < 0.01) were significantly higher, and mean serum 25-hydroxyvitamin D (25-OHD) was significantly lower in the blacks than in the whites (6±1 vs. 20±2 ng/ml, P < 0.001). Mean urinary sodium and 24-h creatinine clearance were the same in the two groups, whereas mean urinary calcium was significantly lower (101±14 vs. 166±13 mg/d, P < 0.01) and mean urinary cyclic AMP was significantly higher (3.11±0.47 vs. 1.84±0.25 nM/dl glomerular filtrate, P < 0.01) in the blacks. Further, the blacks excreted an intravenous calcium load, 15 mg/kg body weight, as efficiently as the whites (49±3 vs. 53±3%, NS). Mean serum Gla protein was lower in blacks than in whites (14±2 vs. 24±3 ng/ml, P < 0.02), and increased significantly in both groups in response to 1,25(OH)2D3, 4

were measured in eight adult anephric subjects. All were undergoing hemodialysis and three of them were receiving vitamin D, 50,000 or 100,000 U/d. Serum vitamin D was elevated in two of the patients given vitamin D and was abnormally low in the others. Mean serum 25-OHD was increased in patients given vitamin D (94.0±7.6 ng/ml) and was normal in the others (16.4±0.9 ng/ml, P < 0.001). Mean serum 24,25(OH)2D was normal in patients given vitamin D (1.38±0.27 ng/ml) and was low in the others (0.25±0.08 ng/ml, P < 0.001). Serum 24,25(OH)2D correlated significantly with serum 25-OHD (r = 0.848, P < 0.01). Mean serum la,25(OH)2D determined by receptor assay was 5.8±1.9 pg/ml in patients who were not given vitamin D and was 14.1±0.6 in those who were given vitamin D (P < 0.001). Serum la,25(OH)2D correlated significantly with serum 25-OHD (r = 0.911, P < 0.01). Mean serum la,25(OH)2D, measured by bioassay, was 8.3±1.9 pg/ml in patients who were not given vitamin D and was 15.9±2.4 pg/ml in those who were given vitamin D (P < 0.05). There was a significant correlation between the values for serum la,25(OH)2D obtained with the two methods (r = 0.728, P < 0.01). The results (a) provide evidence in man for extrarenal production of both 24,25(OH)2D and, by two independent assays, of la,25(OH)2D, and (b) indicate that serum

As compared to nonobese white men and women, age-matched nonobese black subjects and obese white individuals show alterations in the vitamin D-endocrine system that are characterized by increases in mean serum immunoreactive parathyroid hormone (PTH), serum 1,25-dihydroxyvitamin D [1,25-(OH)2D], and urinary cyclic adenosine 3,5-monophosphate (cAMP) and by decreases in mean serum 25-hydroxyvitamin D (25 OHD) and in urinary calcium. Thus, both groups show secondary hyperparathyroidism which is associated with increased renal tubular reabsorption of calcium and increased renal synthesis of 1,25-(OH)2D. In view of these findings, studies were conducted in 10 obese black subjects (3 men and 7 women) and in 12 nonobese black individuals (7 men and 5 women), ranging in age from 20 to 35 yr, to determine whether obesity influences the vitamin D-endocrine system in blacks. Body weight averaged 99 +/- 4 kg in the obese and 73 +/- 3 kg in the nonobese subjects (p less than .001). All of them were hospitalized on a metabolic ward and were given a constant daily diet containing 400 mg of calcium, 900 mg of phosphorus, 110 meq of sodium, 65 meq of potassium, and 18 meq of magnesium.(ABSTRACT TRUNCATED AT 250 WORDS)