Forearm vascular alpha 1-adrenergic blockade by verapamil.
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.
Abernethy
D R
DR
Division of Clinical Pharmacology, Brown University, Providence, RI 02908.
Winterbottom
L M
LM
D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005542:Forearm / Q000098:blood supply*; D006801:Humans; D007261:Infusions, Intra-Arterial; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D010656:Phenylephrine / Q000008:administration & dosage; D011433:Propranolol / Q000008:administration & dosage; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D014655:Vascular Resistance / Q000187:drug effects; D014700:Verapamil / Q000008:administration & dosage / Q000494:pharmacology*
D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D011433:Propranolol; D014700:Verapamil