Calcium entry blockade and alpha-adrenergic vascular reactivity in human beings: differences between nicardipine and verapamil.
The interference by two unrelated calcium entry blockers, nicardipine and verapamil, with the forearm vascular response to graded exogenous norepinephrine was evaluated in two groups (n = 6 each) of patients with uncomplicated hypertension. Drugs were infused into the brachial artery at systemically ineffective rates and forearm blood flow was measured by venous plethysmography. Nicardipine (1 microgram/dl forearm tissue/min) relaxed forearm arterioles and antagonized the vasoconstrictor effect of norepinephrine, whereas verapamil (1 microgram/dl forearm tissue/min) was ineffective, although vasodilating to a comparable extent. Therefore, functional alpha-antagonism may contribute to the vasodilating and, possibly, the antihypertensive effect of nicardipine but, apparently, not verapamil. The data further stress the heterogeneity of calcium channel entry blockers even in human beings.
Pedrinelli
R
R
Hypertension Unit, I Clinica Medica, University of Pisa, Italy.
Taddei
S
S
Salvetti
A
A
D000328:Adult; D005260:Female; D005542:Forearm / Q000098:blood supply; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D006973:Hypertension / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009529:Nicardipine / Q000494:pharmacology*; D009638:Norepinephrine / Q000037:antagonists & inhibitors; D010646:Phentolamine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D012039:Regional Blood Flow / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*; D014700:Verapamil / Q000494:pharmacology*
D011942:Receptors, Adrenergic, alpha; D006632:Histamine; D014700:Verapamil; D009529:Nicardipine; D009638:Norepinephrine; D010646:Phentolamine