Reactivity to bradykinin and potassium of the isolated duodenum from rats with genetic and renal hypertension.

The biphasic (relaxation-contraction) response of the isolated duodenum was used to study the reactivity of non-vascular smooth muscles in genetic (SHR) and renal hypertensive rats compared to their respective controls (WKY and Wistar). For the contractile component of the response to bradykinin, the duodenum from WKY rats was more sensitive, whereas the duodenum from SHR was both more sensitive and hyperreactive, compared to that from Wistar rats. The relaxant component of the response to bradykinin was present in the duodenum of both WKY rats and SHR, but was concentration-dependent only in the WKY group. The relaxant response to K+ was very small in SHR, and was not concentration-dependent. The concentration-response curves for relaxant responses to adrenaline and for contractile responses to acetylcholine did not differ in the SHR and WKY groups. Ca2+/Mg2+-ATPase activity was found to be markedly reduced in the SHR group. No qualitative or quantitative differences were observed between the responses of the duodenum of renal hypertensive rats and those of their normotensive controls. It is proposed that the altered reactivity of the SHR duodenum is due to changes in ion handling by the smooth muscle cell membrane.