A B S T R A C T The effects of several prostaglandins (PG) and a highly purified preparation of cholera enterotoxin (CT) on intestinal mucosal adenyl cyclase activity and the effect of CT on intestinal mucosal cyclic 3',5'-adenosine monophosphate concentration were determined in guinea pig and rabbit small intestine and were correlated with the effects of the same agents on ion transport. Adenyl cyclase activity, measured in a crude membrane fraction of the mucosa, was found at all levels of the small intestine with the highest activity per milligram protein in the duodenum. The prostaglandins, when added directly to the assay, increased adenyl cyclase activity; the greatest effect (2-fold increase) was obtained with PGE1 (maximal effect at 0.03 mM) and PGE2. The prostaglandins also increased short-circuit current (SCC) in isolated guinea pig ileal mucosa, with PGE1 and PGE2 again giving the greatest effects. The prior addition of theophylline (10 mM) reduced the subsequent SCC response to PGE1 and vice versa. It was concluded, therefore, that the SCC response to PGE1, like the response to theophylline, represented active Cl secretion. CT increased adenyl cyclase activity in guinea pig and rabbit ileal mucosa when preincubated with the mucosa from 1 to 2.5 hr in vitro or for 2.5 hr in vivo but not when added directly to the assay. The increments in activity caused by PGE1 and NaF were the same in CT-treated and control mucosa. Cyclic 3',5'-AMP concentration in rabbit ileal mucosa was increased 3.5-fold after a 2 hr preincubation with CT in vitro. Phosphodiesterase activity in the crude membrane fraction of the mucosa was unaffected by either CT or PGE,. A variety of other agents including insulin, glucagon, parathormone, thyroid-stimulating hormone, L-thyroxine, thyrocalcitonin, vasopressin, and epinephrine all failed to change adenyl cyclase activity. It is con-

A B S T R A C T Vasoactive intestinal peptide (VIP), originally isolated from hog small intestinal mucosa, has been shown to cause small intestinal secretion. More recently, this peptide has been identified in the plasma and tumors of patients with the so-called "pancreatic cholera" syndrome. In order to explore the possible role of VIP in the pathogenesis of this syndrome, we examined the effects of this peptide and other hormones on the cyclic AMP levels, adenylate cyclase activity, and ion transport in in vitro preparations of ileal mucosa. In rabbit ileal mucosa, VIP (20 usg/ml) caused a prompt fivefold increase in cyclic AMP level, whereas nine other hormones, which have been postulated to cause intestinal secretion, failed to exert such an effect. Pentagastrin and glucagon also failed to increase cyclic AMP levels in canine ileal mucosa. An increase in mucosal cyclic AMP levels was observed at a VIP concentration of 0.1 4g/ml and appeared to be nearly maximal at 2.0 Ag/ml. VIP (100 sg/ml) stimulated adenylate cyclase activity in a membrane preparation from rabbit ileal mucosa. Secretin (6.0 X 10-M) failed to do so. When added to the serosal side of isolated rabbit ileal mucosa clamped in an Ussing chamber, VIP (2 ug/ml) increased short-circuit current (SCC) and caused net secretion of both C1 and Na. Net Cl secretion exceeded net Na secretion. These effects of VIP on mucosal cyclic AMP metabolism and ion transport are similar to those observed with cholera enterotoxin and certain prostaglandins. VIP was also tested with normal human Dr. Kimberg is the recipient of a Research Career Development Award, AM-19377.

A B S T R A C T It is generally recognized that glucocorticoid administration may diminish calcium absorption in vivo as well as the active transport of calcium by the intestine in vitro. Recent studies by others have emphasized the possibility of an alteration in the metabolism of vitamin D to 25-hydroxycholecalciferol in accounting for the steroid effects on calcium absorption. The results obtained in the present studies fail to support this hypothesis.The present studies confirm that the administration of cortisone or other glucocorticoids to the rat interferes with the active transport of calcium by duodenal gut sacs in vitro. This abnormality is not due to an alteration in the permeability of the intestine to calcium, and it cannot be corrected by the administration of either massive doses of vitamin D3 or modest doses of 25-hydroxycholecalciferol. Experiments concerned with the effects of cortisone on the level of the vitamin D-dependent duodenal calcium-binding protein, the amount of bioassayable vitamin D activity in the mucosa, and the distribution and metabolism of 'H-vitamin D3, did not provide evidence in favor of a hormone-related defect in either the localization of vitamin D or its metabolism to 25-hydroxycholecalciferol. Alterations in the transport of iron and D-galactose, not dependent on vitamin D, suggest that cortisone treatment may be responsible for more than a simple antagonism to the effects of vitamin D.The results of the present studies indicate that cortisone administration affects the cellular mechanisms mediating calcium transport in a manner that is opposite to the

Vitamin D is required for the active transport of calcium in vitro. Small doses of vitamins D2 and D3 restore the mechanism in depleted rats, and this provides a sensitive bio-assay for the vitamin, independent of an antirachitic effect. Vitamin D influences calcium transfer in all segments of the small intestine, and maximal increments are observed in the duodenum. The effect of vitamin D requires oxidative metabolism in vitro, is maximal where active transport is maximal, and the sterol increases the maximal rates of active transport of calcium. Consequently, vitamin D influences calcium transport by affecting primarily the active mechanism rather than by simple diffusion. Experiments with various monosaccharides demonstrate that two distinct steps are involved in the active transport mechanism in duodenum. Vitamin D is required for both of the steps.