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  • Title: Forearm vascular alpha 1-adrenergic blockade by verapamil.
    Author: Abernethy DR, Winterbottom LM.
    Journal: Clin Pharmacol Ther; 1990 Jun; 47(6):755-9. PubMed ID: 2162750.
    Abstract:
    With use of direct brachial artery infusion and measurement of forearm blood flow and vascular resistance by strain gauge plethysmography, the effect of verapamil on phenylephrine-induced vasoconstriction was determined. Seven healthy men (age range, 19 to 47 years; weight range, 68 to 108 kg; mean blood pressure, 74 to 100 mm Hg; five nonsmokers) were systemically beta-blocked with intravenous administrations of 10 mg propranolol. Each subject then received ascending doses of phenylephrine (0.191 to 7.6 micrograms/min) alone and with concurrent verapamil (19.1 micrograms/min) by brachial arterial infusion. Dose-ratio during verapamil infusion compared with control was 8.1 (p less than 0.05). No change in slope of the phenylephrine dose-response curve was noted; however, consistent with the dose ratio, verapamil shifted the curve to the right with a decrease in the y intercept determined by linear regression (60.0 versus 40.3 mm Hg ml/100 ml forearm volume/min; p less than 0.05). Verapamil-induced attenuation of forearm vasoconstriction elicited by phenylephrine indicates that, in humans, in vivo verapamil forearm vasodilating effects are, in part, a result of alpha 1-adrenergic blockade.
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