Differences in inositol phosphate production in blood vessels of normotensive and spontaneously hypertensive rats

1 Total inositol phosphate formation was measured in labelled femoral and iliac arteries and veins of 14 week‐old spontaneously hypertensive rats (SHR) and age‐matched Wistar Kyoto (WKY) controls, either unstimulated or in the presence of noradrenaline. 2 Basal levels of [ 3 H]‐inositol phosphates and [ 3 H]‐phosphatidylinositol were significantly enhanced in SHR femoral artery, but not in the other 3 vessels, compared with WKY. 3 Noradrenaline stimulated phosphoinositide hydrolysis in all four vessels of SHR and WKY. Pretreatment with prazosin (10 −7 –10 −6 m ) but not with yohimbine (10 −7 m ), inhibited the noradrenaline‐induced inositol phosphate formation indicating an α 1 ‐adrenoceptor‐mediated response. 4 In the femoral artery of SHR compared to WKY, [ 3 H]‐inositol phosphate accumulation induced by noradrenaline (10 −7– 10 −5 m ) was significantly reduced when expressed relative to basal values although the response to higher concentrations (10 −4 –10 −3 m ) was not altered. In contrast, a significant reduction of inositol phosphates was seen only with 10 −7 m noradrenaline when absolute values were compared. In the other three vessels, no difference in noradrenaline‐induced [ 3 H]‐inositol phosphate formation was observed between strains. 5 These data suggest that phosphoinositide hydrolysis‐mediated by α 1 ‐adrenoceptors may be reduced in some but not all blood vessels of adult SHR.