The effect of somatostatin and enkephalin on ion transport in the intestine.

SRIF and enkephalin stimulate net Na and C1 absorption in the rabbit ileum and appear to do so primarily by stimulating the coupled influx of Na and C1 across the brush border membrane. The stimulatory effect of enkephalin on ion transport is blocked by verapamil and Ca-free solution, indirectly indicating that enkephalin may work as a Ca-channel blocker. The resultant lowering in cytosolic calcium level stimulates Na and C1 absorption. SRIF was able to block the effect of cyclic AMP-dependent and cyclic AMP-independent secretogogues in the rat colon without affecting cyclic AMP levels suggesting that it is inhibiting a distal step in the secretory pathway, probably involving a final common pathway. SRIF infusion blocked diarrhea in a patient with the carcinoid syndrome, indicating that it may be therapeutically useful in the treatment of secretory diarrheas. The antidiarrheal effect of opiates is probably due in part to their effect on electrolyte absorption, rather than an effect solely on intestinal motility.