Insulin action on different smooth muscle preparations.

1. The importance of insulin in diabetic gastro-intestinal complications has been postulated. The present study was designed to investigate short-term effect of insulin on different smooth muscles isolated from non-diabetic animals. 2. The contractile responses of isolated guinea-pig ileum to acetylcholine and histamine and the serotonin-induced contractions of rat stomach fundus strips were inhibited by insulin in a non-competitive manner. The contractions of rat vas deferens elicited by noradrenaline and tyramine were also inhibited in the presence of insulin. 3. Insulin caused dose-dependent relaxation on the isolated rat duodenum. The relaxing response to insulin was not affected in the presence of atropine, phentolamine, propranolol, nicotinic acid, tetrodotoxin, tetraethylammonium, ouabain and nifedipine. The relaxing effect of insulin on the isolated rat duodenum was inhibited by sodium orthovanadate, trifluoperazine, verapamil, aspirin and dexamethasone, non-competitively. 4. The above results strongly suggest that the relaxing or inhibitory effect of insulin on the smooth muscles is closely related with prostanoid metabolism. Furthermore, it is concluded that this effect of insulin on the smooth muscles may be due to activation of Ca2+-pump ATPase(s).