Seven patients with disordered calcium metabolism and high normal or elevated serum 1, 25-dihydroxyvitamin D [1, 25-(OH)2D] were studied before and after the administration of 24, 25-(OH)2D3 to determine its effects on calcium metabolism. Despite a significant increase in the mean serum 24, 25- (OH)2D level [2.1 ± 0.6 (±SE) to 16.7 ± 6.2 nmol/L; P<0.05] after a daily dose of 20 μg for 1 month, there were no consistent changes in serum calcium, immunoreactive PTH, or 1, 25- (OH)2D concentrations. Intestinal calcium absorption and urinary calcium excretion rose slightly during 24, 25-(OH)2D administration in the majority of the patients. In the three patients in whom it was measured, serum 1, 24, 25-trihydroxyvitamin D levels did not change (19 ± 5 vs. 20 ± 5 pmol/L). We conclude that exogenous 24, 25-(OH)2D3 at this dose has no significant antagonistic action on 1, 25-(OH)2D and may have weak agonistic action.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Clinical Biochemistry
- Biochemistry, medical