The Duodenal 1α, 25-Dihydroxyvitamin D₃ receptor in rats with experimentally induced diabetes

Studies in the rat with streptozotocin-induced diabetes of short and long duration revealed decreased circulat-ing lα, 25-dihydroxyvitamin D [1, 25-(OH)₂D] levels and an in-tact 1, 25-(OH)₂D₃ duodenal cytosolic receptor with a sedimentation coefficient of 3.3S. Whereas no significant alterations in the equilibrium dissociation constant (K_d) were observed in the diabetic animals, the number of l, 25-(OH)₂D₃-binding sites was increased in the animals with short term (235 ± 48 us. 100 ± 15 fmol/mg protein) and long term (521 ± 60 vs. 119 ± 15 fmol/mg protein) diabetes. The data are consistent with the hypothesis that alterations in intestinal calcium absorption previously observed in the diabetic state are due, at least in part, to dynamic relationships between circulating 1, 25-(OH)₂D concentrations and the number of intestinal l, 25(OH)₂D₃-binding sites.