Decreased gastro-intestinal responses to salbutamol and serotonin in streptozotocin-induced diabetes: improving effect of insulin in vivo and in vitro.

1. Decreased gastro-intestinal responses to salbutamol (sal) and serotonin (5-HT) in experimental diabetes have been postulated. The present study was designed to investigate whether in vivo and in vitro insulin treatments improve the decreased gastro-intestinal responses. 2. In vivo insulin treatment (166.7 micrograms/kg/day i.p.) for 6 weeks is able to improve both decreased gastro-intestinal beta-adrenergic and serotonergic responses. 3. Insulin incubation in bathing medium for 4-5 hr enhances the decreased gastro-intestinal responses to sal, but not to 5-HT. 4. The above results strongly suggest that the improving effect of insulin on the gastro-intestinal beta-adrenergic responses is direct in nature. In contrast, the improving effect on insulin on the serotonergic responses occurs via an indirect mechanism.