Norepinephrine stimulation of phosphoinositide hydrolysis in rat cerebral cortex is associated with the alpha1-adrenoceptor.

Norepinephrine (NE) and the selective alpha1-adrenoceptor agonist phenylephrine (PE) both markedly stimulate the formation of [3H]inositol phosphates in a concentration-dependent manner upon incubation with [3H]myo-inositol. The selective alpha2 agonist, clonidine, did not significantly alter [3H]inositol phosphate formation, even at concentrations as high as 10(-3) M. The alpha1 antagonist prazosin (IC50, 0.036 microM) was 300 times more potent than the alpha2 antagonist yohimbine (IC50, 10.7 microM) as an inhibitor of NE (10(-4) M)-stimulated phosphatidylinositol (PI) hydrolysis. These results indicate that the alpha1-, but not the alpha2-adrenoceptor subtype in rat brain is coupled to phosphoinositide hydrolysis.