Influence of glucocorticoids on calcium absorption in different segments of the rat intestine.

Glucocorticoids enhance the movement of fluid and sodium in the duodenum, thereby resulting in an increase in the passive transport of calcium. Since passive transport of calcium predominates in the distal intestinal segments, the influence of glucocorticoids on calcium and fluid transport in the duodenum, mid-jejunum, ileum, and colon of the rat was studied. Calcium transport and fluid absorption was determined by the in vivo ligated loop technique. One segment was ligated in each animal. Under either normal osmolarity or hypertonic conditions, administration of cortisone stimulated intestinal fluid absorption in each segment of the small intestine, but not in the colon. Since the final fluid sodium concentration was not altered, cortisone enhanced net sodium absorption in proportion to the increase in fluid transport. Glucocorticoids inhibited the active transport of calcium in the proximal regions of the small intestine by bidirectional changes in calcium flux. However, the inhibitory effect was not apparent under the conditions where passive transport predominates. The stimulation of passive transport in the mid-jejunum overcomes the inhibition of active transport. In the ileal region, glucocorticoids increased active transport of calcium by 165%, whereas the enhancement of calcium transport under conditions where passive transport predominated reached 217%. This result indicates that both active and passive transport of calcium were enhanced by glucocorticoid treatment. In the colon, glucocorticoids increased active transport by 170%. However, the magnitude of the increase in calcium transport was less under conditions where passive transport predominates (129%), indicating that glucocorticoids stimulate the active transport of calcium in the colon with no appreciable stimulation of passive transport.