ENHANCED ARTERIAL CONTRACTILITY TO NORADRENALINE IN DIABETIC RATS IS ASSOCIATED WITH INCREASED PHOSPHOINOSITIDE METABOLISM

The purpose of this study was to investigate whether the increased contractile responsiveness of aortae from male rats with 12-14 week streptozotocin-induced diabetes to noradrenaline is associated with alterations in phosphoinositide metabolism. The contractile response to noradrenaline (10-mu-M) in both the presence and absence of extracellular calcium was significantly enhanced in aortae from diabetic rats. No significant differences were found between control and diabetic arteries in the basal incorporation of P-32 and [H-3]myo-inositol into phosphoinositides, or in the basal accumulation of [P-32]phosphatidic acid and [H-3]inositol phosphates. However, noradrenaline (10-mu-M) caused significantly greater breakdown of [P-32]phosphatidylinositol 4,5-bisphosphate and formation of [P-32]phosphatidic acid and [H-3]inositol phosphates in diabetic aortae than in control preparations. The production of [H-3]inositol phosphates induced by noradrenaline was selectively reduced by the alpha-1-adrenoceptor antagonist, prazosin, in both control and diabetic tissues. These results indicate that phosphoinositide metabolism in response to noradrenaline via stimulation of alpha-1-adrenoceptors is enhanced in aortae from chronic streptozotocin-diabetic rats. The increase in inositol 1,4,5-trisphosphate and 1,2-diacylglycerol production that presumably results could be responsible, at least in part, for the enhanced contractile response of aortae from diabetic rats to noradrenaline.