The peptidergic neural control of the feline pylorus

By immunohistochemistry the three neuropeptides enkephalin, substance P, and VIP were all localized to numerous nerve fibers in the smooth muscle layer and the myenteric plexus of the feline pylorus. The motor activity of the pylorus was studied by recording changes in the volume flow of body-warm saline through the sphincter at constant perfusion pressure in anesthetized cats. Efferent electric stimulation of the cervical vagi (8 V; 5 ms; 8 Hz) elicited a noncholinergic, nonadrenergic pyloric contraction, which was blocked by infusion of the opiate receptor antagonist naloxone. The peptides were injected into a regional gastric artery to the pylorus antrum. Enkephalin and substance P in micronanomolar doses resulted in a prompt contraction of 3 - 5 min duration. Equimolar doses of naloxone blocked the enkephalin-induced contraction, and atropine blocked the SP contraction. On the other hand, VIP caused a prompt dilatation, which could not be blocked in this study. Altogether the findings suggest a peptidergic motor control of the feline pylorus using several transmission mechanisms.