Abstract
Vasoactive intestinal polypeptide (VIP) has been shown to be present in some neurones of the myenteric plexus by immunohistochemical techniques. It was reported that avian pancreatic polypeptide (APP) inhibited the vasodilation induced by VIP and chorda-lingual nerve stimulation in the cat submandibular gland (Lundberg et al.,Acta.Physiol.Scand.,1980,110,199). The purpose of the present experiment is to investigate whether APP acts as a VIP antagonist by using various tissues innervated by non-cholinergic, non-adrenergic nerves in the gastrointestinal tract. APP was isolated and purified from chicken pancreas by the method of Kimmel et al. (J.Biol.Chem., 1975,250,9369). The isolated APP (0.48-12nmole) caused a dose-dependent inhibition of the vasodilation induced by VIP and chorda-lingual nerve stimulation in the cat submandibular gland as reported by Lundberg et al. ‘1980). In the cat colon, APP (0.4-10nmole) elicited a dose-dependent vasoconstriction and partially inhibited the atropine-resistant vasodilation induced by VIP and pelvic nerve stimulation, but not significantly that induced by bradykinin. On the other hand, APP failed to inhibit the relaxation caused by either transmural electrical stimulation or VIP in the presence of atropine and guanethidine in isolated chick rectum and fundic strips of guinea-pig and rat. Furthermore, APP had no inhibitory effect on the gastric relaxation induced by the vago-vagal reflex and by the close arterial injection of VIP in the dog stomach. The results suggest that APP may act as an antagonist for the VIP-induced vasodilation of vascular smooth muscles, but not for the VIP-and the non-adrenergic nerve stimulation-induced relaxation of gastrointestinal smooth muscles.
Published Version
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