Diabetes mellitus is associated with a decrease in vasoactive intestinal polypeptide content of gastrointestinal tract of rat

Vasoactive intestinal polypeptide (VIP) is an inhibitory non adrenergic, non-cholinergic transmitter, which mediate in the relaxation of sphincters of the gastrointestinal tract. The aim of this study was to determine whether there is a change in the pattern of innervation and tissue content of VIP in the rat gastroduodenum after the onset of streptozotocin (STZ)-induced diabetes mellitus. Diabetes was induced by a single intraperitoneal injection of STZ (60mgKg^-1). Four weeks after the induction of diabetes mellitus, the rats were anaethetised and the pancreata were removed for further processing. VIP was localized and measured in normal and diabetic rat gastroduodenal tissues by immunohisto-chemistry and radioimmunoassay, respectively. VIP immunoreactivity was stronger in the ganglion cells of the submucosal and myenteric plexuses of the gastric antrum and duodenum of normal rats (n = 6) when compared to that of diabetic rats (n = 6). Moreover, the number of VIP-positive neurons was significantly lower in the gastrointestinal tract of diabetic rats compared to normal. The VIP content of the gastric antrum and duodenum of diabetic rat was significantly lower (p < 0.05) than that of normal rat. In contrast to the lower tissue levels of VIP in the gastroduodenal segment of diabetic rats, the plasma level of VIP was significantly higher (p < 0.04) in diabetic rat compared to normal. The plasma level of VIP in normal rats was comparable to that measured in normal human beings. A low tissue level of VIP in the gastroduodenal tract of diabetic rat may contribute in part to the abnormal gut motility observed in diabetic patients.