Influence of calcium entry blockade on alpha 1- and alpha 2-adrenoceptor mediated vasoconstriction in the forearm of hypertensive patients.

The influence of treatment with the calcium entry blockers PY 108-068 (PY) and PN 200-110 (PN) on alpha 1- and alpha 2-adrenoceptor mediated vasoconstriction has been investigated in the forearms of hypertensive patients. Changes in forearm vascular resistance (FVR) in response to the intra-arterial infusion of drugs were determined at the end of a placebo period and after 2-4 weeks of treatment with PY or PN. The drugs used were the selective agonists methoxamine (alpha 1) and B-HT 933 (alpha 2). During placebo, basal FVR was dose-dependently increased by methoxamine and B-HT 933. Basal blood pressure was lowered during PN but not during PY. Treatment with the calcium entry blockers did not influence the effect of methoxamine, but the vasoconstriction induced by B-HT 933 was attenuated by both of the calcium entry blockers. These results confirm the findings in animal studies that calcium entry blockers preferentially inhibit the alpha 2-adrenoceptor mediated vasoconstriction induced by selective agonists.