ABSTRACT
The effects of frusemide, ethacrynic acid and chlorothiazide were studied in the Wistar Kyoto (WKY) rats and spontaneously hypertensive rat (SHR) portal veins in vitro. Frusemide produced concentration-dependent contractions of the portal vein from both WKY control and SHR. The WKY were more sensitive (as judged by the EC50) whilst a greater maximal response was generated in the SHR. The contractile response to frusemide in WKY rats was attenuated reversibly by phenoxybenzamine whereas the latter was ineffective in the SHR. Ethacrynic acid produced reductions of the myogenic rhythmic contractions of the portal vein in a concentration-related manner in both WKY and SHR. The inhibitory action of ethacrynic acid was greater in the SHR than in the WKY control rats. The inhibitory action of ethacrynic acid was blocked by propranolol suggesting the involvement of beta adrenoceptors. Chlorothiazide, on its own, had no observable effect on the portal vein. However, it reduced the sensitivity of the vein to noradrenaline and K+. This reduction was greater in the SHR than in the WKY. It is concluded that some of the observed effects of these diuretics may contribute beneficially to their anti-hypertensive actions.
