Lack of effect of ovariectomy on the metabolism of vitamin D and intestinal calcium-binding protein in female rats

The metabolism of 25-hydroxycholecalciferol (25-(OH)D₃), plasma concentration of 1,25-dihydroxycholecalciferol (1,25-(OH)₂D₃) and the amount of calcium-binding protein (CaBP) in duodenal mucosa were determined in ovariectomized rats and were compared with data observed in normal age-matched cyclic rats. Sephadex LH-20 and high-pressure liquid chromatography were used for the study of the metabolism of 25-(OH)D₃. The concentration of 1,25-(OH)₂D₃ in plasma and prolactin in serum were measured by radioimmunoassay. Calcium-binding protein in duodenal mucosa was determined immunologically using electroimmunodiffusion. The results showed that the lack of ovarian hormones and low prolactin levels observed in ovariectomized rats did not promote a significant change in the metabolism of 25-(OH)D₃, in the levels of 1,25-(OH)₂D₃ in the circulation or in the amount of CaBP in duodenal mucosa. It is possible that the regulation of 25-(OH)D₃ by sex hormones is restricted to the state of calcium stress such as during egg-laying in birds or pregnancy and lactation in mammals.