Verapamil interacts in vitro with alpha 2-adrenoceptors but does not modify alpha 2-receptivity in vivo.
The kind of interaction of two structurally different calcium channel blockers (verapamil and nicardipine) with both alpha 2-adrenergic agonist and antagonist binding on human platelets was investigated. Only verapamil, but not nicardipine, interacted in vitro with platelet alpha 2-adrenoceptors on [3H]-yohimbine or [3H]-UK 14,304 binding. Verapamil behaves as a weak antagonist competitor for alpha 2-adrenoceptors. In patients with mild essential arterial hypertension, the number of platelet alpha 2-adrenoceptors as well as velocity of aggregatory response to adrenaline, are significantly decreased: -21 and -25%, respectively (p less than 0.05). Verapamil (120 mg t.i.d. orally during 1 month) failed to modify the platelet alpha 2-adrenoceptor number or the adrenaline-induced platelet aggregation in hypertensive patients. These results show that, although interacting in vitro, verapamil does not modify the alpha 2-adrenergic receptivity after 1 month treatment in humans.
Galinier
M
M
Laboratoire de Pharmacologie Médicale et Clinique, INSERM U 317, Centre Hospitalier Universitaire, Faculté de Médecine, Toulouse, France.
Senard
J M
JM
Valet
P
P
Boneu
B
B
Galinier
F
F
Montastruc
J L
JL
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000328:Adult; D001667:Binding, Competitive / Q000187:drug effects; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D006801:Humans; D006973:Hypertension / Q000503:physiopathology; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D009529:Nicardipine / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D014700:Verapamil / Q000494:pharmacology*; D015016:Yohimbine / Q000378:metabolism
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D010975:Platelet Aggregation Inhibitors; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D014700:Verapamil; D009529:Nicardipine; D004837:Epinephrine