Effect of substance P and capsaicin on stomach fundus and ileum of streptozotocin-diabetic rats.

The in vitro responses of longitudinal preparations of rat stomach fundus and ileum to capsaicin at 1, 8, 4, 16 and 26 weeks and to substance P at 1 and 8 weeks from diabetes induction were studied. The results were compared with those obtained in age-matched control rats. The contractile responses to exogenous substance P and capsaicin were not affected in the stomach fundus from diabetic rats. Atropine (1 microM) did not antagonize the substance P-induced response whereas it inhibited about 90% of the capsaicin-induced response in controls and about 60% of the response in diabetic rats. At the resting tone, capsaicin induced a relaxation followed by a contraction in stomach fundus of control rats. Only a contraction was evoked in diabetic rats. In carbachol (0.05-0.1 microM) pre-stimulated strips, a complete restoration of the biphasic response was obtained in the diabetic state. The contractile response elicited by exogenous substance P was not significantly increased in the ileum preparations from diabetic rats; nevertheless the EC50 value for substance P was reduced 8 weeks after the onset of diabetes. The response elicited by capsaicin in the ileum of control rats was also biphasic. The capsaicin-induced contraction was greater in tissue from diabetic rats as compared with controls and relaxation was not evident. An age-related decrease of the contraction was also evident in both groups. Atropine (1 microM) partially antagonized the responses to substance P and capsaicin. The inhibition of the responses with atropine was more evident in control than in diabetic rats. These results suggest that the myogenic actions of several agonists in these two tissues are differently modified in experimental diabetes.