Vasoactive intestinal peptide. An inhibitor of feline gastric smooth muscle in vitro

Intrinsic innervation of the stomach of the fetal pig: an immunohistochemical study of VIP-immunoreactive nerve fibres and cell bodies

Using an immunohistochemical technique, the presence and distribution of vasoactive intestinal polypeptide (VIP) was investigated in cryostat sections, both tangential and transverse, of the fetal pig's stomach. In all fetuses and in all gastric segments investigated, VIP-like immunoreactive (IR) nerve-cell bodies were seen in all intramural ganglia, and VIP-IR nerve fibres were found in all layers of the gastric wall except the tunica serosa. Consequently, VIP-IR nerve fibres were found to form a periglandular network, to accompany arterioles, to interconnect the intramural ganglia, to encircle both VIP-IR-negative and -positive neurons, and were found in all muscle layers. Despite the fact that VIP-IR seems to be restricted to the intramural nervous elements, some non-specific-reacting VIP-IR glandular cells were noticed in the basal parts of the fundic, antral and pyloric gastric glands. The distribution pattern of VIP in the fetal pig resembles that of the adult pig. This suggests a possible functional role for VIP during fetal life and/or puts forward the suggestion that the stomach of a fetal pig from the second half of the gestation period is prepared, from then on, for postnatal function. High similarities with regard to the general distribution pattern of VIP in the stomach have also been noted between the fetal pig and humans, proving once more that the fetal pig can serve as a good animal model in several research areas. Finally, the morphological data provided here may, combined with the physiological significance of VIP, contribute to a better insight into the physiopathology of economically important gastro-intestinal disorders in the pig, such as gastric ulceration.

Responses of porcine gastric and duodenal smooth muscle to VIP

1. Mechanical activity was recorded in isolated muscle preparations from circular and longitudinal layers of gastric fundus, corpus and antrum and from the duodenum of pigs, using conventional organ bath technique. Rectangular current pulses were applied to the muscle strips for electrical field stimulation (EFS). 2. Fundic and circular corpus preparations developed a marked spontaneous tonic activity. Vasoactive intestinal polypeptide (VIP, 10(-9)-10(-7) mol l-1) inhibited this spontaneous activity. This inhibitory effect was not affected by application of tetrodotoxin (TTX) showing its myogenic nature. 3. Pretreatment of fundic and circular corpus preparations with VIP reduced the excitatory responses to substance P, bombesin, serotonin and histamine, but it had no effect on the acetylcholine (ACh)-induced tonic and phasic activity. 4. Longitudinal duodenal preparations showed purely phasic activity which was almost insensitive to VIP. In circular duodenal preparations particularly strong spontaneous tonic contractions were observed which could be inhibited by VIP. 5. Circular duodenal preparations excised 3-5 cm postpyloric had a spontaneous tone which could reach up to 80% of the maximum contractions induced by 10(-4) mol l-1 ACh. These preparations were chosen for further pharmacological studies and for experiments with EFS. VIP was the most powerful substance for the inhibition of spontaneous tone, followed by serotonin, PGE2 and bradykinin. This type of preparation exhibited particularly strong inhibitory effects to EFS; even single stimuli could induce near maximum relaxation. The inhibition induced by EFS was unaffected by treatment with ATP, guanethidine, atropine, methysergide and apamin. TTX completely abolished the EFS-induced relaxation, showing its neurogenic nature. 6. Porcine circular duodenum is a good model for studying the transmitter system of the non-adrenergic, non-cholinergic (NANC) innervation. The results are consistent with the assumption that VIP is the transmitter in this system, although the very slow time-course of the VIP-induced inhibition in comparison with the EFS-induced inhibition is not consistent with this notion.