Effects of diabetes and vitamin D-depletion on duodenal and ileal calcium transport in the rat.

Abstract

We compared effects of vitamin D depletion and alloxan-induced diabetes on intestinal calcium transport in growing rats. Transport of45Ca was studied using everted sacs of duodenum and ileum. Diabetic rats were compared with matched controls (diabetes studies); vitamin D-depleted animals were compared with depleted animals repleted with vitamin D 48 hrs prior to study (vitamin D studies). Duodenal calcium transport was reduced by half or less in experimental groups (diabetic or vitamin D-depleted rats) when compared with corresponding controls (control rats matched with diabetics or vitamin D-repleted animals matched with depleted animals):a) for serosal-to-mucosal (S/M) concentration ratios; andb) per unit weight of mucosa as net transport into serosal medium or net disappearance from mucosal medium. Based on transport into the serosal medium per unit of mucosa, ileal calcium transport was decreased in the vitamin D-depleted group compared with the vitamin D-repleted group in vitamin D studies. In contrast, in diabetes studies ileal calcium transport into the serosal medium was the same in diabetic and control animals. The finding that diabetes and vitamin D depletion have the same effects on duodenal calcium transport agrees witha) lack of specific, vitamin D-dependent duodenal calcium-binding protein in diabetes, andb) restoration of duodenal calcium transport in diabetics by either 1.25-dihydroxycholecalciferol or 1α-hydroxycholecalciferol. Depression of ileal calcium transport by vitamin D-depletion but not by diabetes shows the specificity of intestinal site with respect to mechanisms and control of calcium transport. Diabetes complements vitamin D depletion as a means for studying intestinal calcium transport.