Effect of nifedipine and verapamil on alpha-receptor-activation in patients with essential hypertension.
The question of whether the hypotensive effect of calcium entry blockers involves an interaction with alpha-adrenergic receptors was examined. The effect of nifedipine subl. (20 mg, n = 9) and of verapamil p.o. (160 mg, n = 9) on the pressor effect of the unselective alpha-adrenergic agonist noradrenaline, as well as on 3H-yohimbine binding to platelet alpha 2-adrenoceptors was studied in patients with essential hypertension. In addition, the effect of nifedipine on reactivity to the selective alpha 1-adrenergic agonist phenylephrine was investigated (n = 9). Nifedipine caused a significant reduction of reactivity to noradrenaline (P less than 0.01), along with a significant decrease in binding sites (P less than 0.01). Affinity to the alpha 2-receptors was unchanged. Verapamil, although equally effective in lowering blood pressure, had no effect on the pressor response or binding sites. The pressor effect of the alpha 1-agonist phenylephrine was reduced (P less than 0.01) by nifedipine. Nifedipine may therefore affect both alpha 1- and alpha 2-adrenoceptors in patients with essential hypertension. Since verapamil did not affect the pressor response to noradrenaline or yohimbine-binding, the interaction with alpha 2-adrenoceptors does not appear to be a general prerequisite for the hypotensive action of calcium entry blockers.
D000328:Adult; D000368:Aged; D001792:Blood Platelets / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004341:Drug Evaluation; D004347:Drug Interactions; D005260:Female; D006801:Humans; D006973:Hypertension / Q000188:drug therapy* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009543:Nifedipine / Q000627:therapeutic use*; D009638:Norepinephrine; D010656:Phenylephrine; D011311:Pressoreceptors / Q000187:drug effects; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000378:metabolism; D014700:Verapamil / Q000627:therapeutic use*; D015016:Yohimbine / Q000097:blood
D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D014700:Verapamil; D009543:Nifedipine; D009638:Norepinephrine