Abnormal vascular phosphoinositide hydrolysis in the spontaneously hypertensive rat

The production of [3H]-inositol phosphates was studied in labelled segments of aorta from spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) controls at 5 and 19 weeks, either unstimulated or in the presence of noradrenaline. Basal hydrolysis of inositol phospholipids was significantly enhanced in young SHR (P less than 0.05) compared to controls but this difference was no longer detected at 19 weeks. Noradrenaline increased [3H]-inositol phosphate accumulation in both SHR and WKY, but maximal hydrolysis was significantly greater in WKY (P less than 0.01), although the ED50 was similar in both groups of animals. These data demonstrate that phosphatidylinositide hydrolysis is enhanced in the young hypertensive rat at the time blood pressure is rising, but that this activity has declined by the time hypertension has reached an established phase. In addition, alpha 1-agonist induction of inositol phospholipid hydrolysis differs in the two species of animals, being reduced in genetically mature hypertensive rats.