Responsiveness of peripheral veins to vasodilators and the effect of nifedipine on α‐adrenergic responsiveness in hypertension

Vasodilators have varying hemodynamic properties that may be important in determining their efficacy for different disorders. We used the dorsal hand vein technique to measure the effects of several vasodilators infused locally and to measure the action of systemically administered nifedipine. The venodilatory effects of hydralazine, verapamil, diazoxide, and nitroglycerin were determined in peripheral veins of healthy subjects. The potency (ED 50 , the dose producing half‐maximal response) was as follows: nitroglycerin (0.0007 μg/min) > verapamil (6.5 μg/min) > diazoxide (75 μg/min) > hydralazine (660 μg/min). The effect of oral nifedipine on α‐adrenergic responsiveness of hand veins was determined. Nifedipine given in therapeutic doses for the treatment of hypertension was associated with a threefold increase in the ED 50 for phenylephrine (92 to 277 ng/min; p < 0.05) and norepinephrine (2.9 to 11.5 ng/min; p < 0.05). Therapeutic doses of nifedipine are associated with measurable shifts in the dose‐response curves to these two α‐adrenergic agonists in the hand vein. The hand vein technique can be used not only to compare the potency of locally infused drugs but also to measure venous effects of va‐soactive drugs at therapeutic concentrations achieved after systemic administration. Clinical Pharmacology and Therapeutics (1991) 50, 192–198; doi: 10.1038/clpt.1991.124