1. The addition of frusemide or bumetanide to perfusion fluid inhibited the response of the isolated mesenteric vascular bed to noradrenaline.
2. Addition of prostaglandin E2 to the perfusion fluid completely restored the response to noradrenaline.
3. Inhibition of prostaglandin secretion by indomethacin with restoration of responses to noradrenaline by the addition of exogenous prostaglandin E2 prevented the inhibitory effect of frusemide or bumetanide on responses to noradrenaline.
4. The inhibitory effects of diuretics on responsiveness to noradrenaline is mediated by blockade of endogenous prostaglandin synthesis.