In vivo calcium transport by rat small intestine

Abstract

Ca transport in the small intestine was studied by in vivo perfusion in adult rats maintained on an adequate intake of Ca and vitamin D. The 40Ca concentration in the perfusion solution was varied from 0. 2-3.4 mM with tracer amounts of 45Ca. Net transport and lumen-to-plasma flux were highest in the duodenum, but rates in the mid intestine and terminal ileum did not differ. Transport against a concentration gradient was demonstrated in all segments. Intestinal tissue 40Ca and 45Ca was lower in the duodenum than in the more distal segments. The gradient between intraluminal and tissue 40Ca was uphill, and that between tissue and serum was downhill at the 3 intestinal levels. These data demonstrate active Ca transport in distal as well as proximal small intestine of the rat and are consistent with the interpretation that the rate-limiting step is at the serosal side of the membrane.