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 fun dus and ileum to capsaicin at 1, 8, 4, 16 and 26 weeks and to substanc e P at 1 and 8 weeks from diabetes induction were studied. The results were compared with those obtained in age-matched control rats. The co ntractile responses to exogenous substance P and capsaicin were not af fected in the stomach fundus from diabetic rats. Atropine (1 mu M) 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 induc ed 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 mu M) pre-stimulated strips, a complete restoration of the bip hasic response was obtained in the diabetic state. The contractile res ponse elicited by exogenous substance P was not significantly increase d in the ileum preparations from diabetic rats; nevertheless the EC(50 ) value for substance P was seduced 8 weeks after the onset of diabete s. The response elicited by capsaicin in the ileum of control rats was also biphasic. The capsaicin-induced contraction was greater in tissu e from diabetic rats as compared with controls and relaxation was not evident. An age-related decrease of the contraction was also evident i n both groups. Atropine (1 mu M) partially antagonized the responses t o substance P and capsaicin. The inhibition of the responses with atro pine was more evident in control than in diabetic rats. These results suggest that the myogenic actions of several agonists in these two tis sues are differently modified in experimental diabetes.