Assessment of 25-hydroxyvitamin D 1 alpha-hydroxylase reserve in postmenopausal osteoporosis by administration of parathyroid extract.
Previous studies have shown that the mean serum concentration of 1,25-dihydroxyvitamin D [1,25-(OH)2D] is lower than normal in patients with postmenopausal osteoporosis. We studied the mechanism of this abnormality in 12 women with postmenopausal osteoporosis and 10 age-comparable normal women. Parathyroid extract (200 U, twice daily for 3 days) was administered to stimulate the enzymatic conversion of 25-hydroxyvitamin D (25OHD) to 1,25-(OH)2D. The serum concentration of 1,25-(OH)2D was lower (P less than 0.05) at a baseline determination in the osteoporotic subjects than in the normal women and increased significantly (P less than 0.001) above basal values after the administration of parathyroid extract in both groups; however, the degrees of increase in the control and osteoporotic subjects were similar. We conclude, at least under the conditions of our study, that 25OHD 1 alpha-hydroxylase is normally responsive to parathyroid hormone in postmenopausal osteoporosis. Thus, the apparently impaired metabolism of 25OHD to 1,25-(OH)2D appears to be secondary to a decrease in factors that abnormally stimulate 25OHD 1 alpha-hydroxylase activity rather than a primary defect in enzyme reserve capacity.
D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000378:metabolism*; D000368:Aged; D004100:Dihydroxycholecalciferols / Q000096:biosynthesis; D005260:Female; D006801:Humans; D008593:Menopause; D008875:Middle Aged; D010024:Osteoporosis / Q000201:enzymology*; D010280:Parathyroid Glands / Q000032:analysis; D010281:Parathyroid Hormone / Q000494:pharmacology*; D013250:Steroid Hydroxylases / Q000378:metabolism*; D014020:Tissue Extracts / Q000494:pharmacology
D004100:Dihydroxycholecalciferols; D010281:Parathyroid Hormone; D014020:Tissue Extracts; D013250:Steroid Hydroxylases; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase