Calcium flux in vivo in the rat duodenum and ileum during pregnancy and lactation

Abstract

Intestinal calcium transport was examined in nonpregnant, pregnant, lactating, and 100 ng 1,25-dihydroxyvitamin D3-dosed rats. Solutions containing 150 mM NaCl, 1 mM Ca, and 0.1 microCi 45Ca were recirculated in vivo through the duodenum and ileum to determine calcium efflux from the lumen, influx into the lumen, and net absorption. In the duodenum of the nonpregnant control rats, efflux of calcium was greater than influx, resulting in net absorption of calcium. In the ileum, calcium efflux and influx were equivalent and there was little net movement of calcium. 1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] significantly increased efflux and net absorption of calcium in the duodenum without affecting influx. In the ileum 1,25(OH)2D3 had no effect on calcium flux. During pregnancy and lactation there was a marked increase in mucosal tissue, and expression of transport data per centimeter of intestine gave different results than transport expressed per gram of dry mucosal tissue. Per centimeter of intestine, duodenal efflux and net absorption, but not influx, increased significantly during pregnancy and to greater extent during lactation. Per gram of dry mucosa, duodenal efflux and net absorption were increased significantly only during lactation, and the increase was comparable with that observed in 1,25(OH)2D3-dosed rats. In the ileum of pregnant and lactating rats, efflux and influx expressed per centimeter of intestine increased to approximately the same extent, and net movement of calcium remained unchanged from the control level. Expression of ileal transport data per gram of dry mucosa resulted in no significant difference in calcium movement during pregnancy and lactation.(ABSTRACT TRUNCATED AT 250 WORDS)