Blockage of clonidine-induced platelet aggregation in rabbits by procainamide.
Procainamide was capable of blocking the alpha 2-adrenergic receptor agonist clonidine-induced platelet aggregation, giving an antagonistic index, pA2, of 5.0 +/- 0.6 and half antagonistic concentration, A2, of 10.4 mumol.L-1. Clonidine showed half efficacy concentrations (EC50) of 44, 82, 182, 485, and 662 nmol.L-1, and affinity parameter (pD2) of 7.4, 7.1, 6.7, 6.3, and 6.2 respectively when different concentrations of procainamide were used as blocking reagent. The results indicated that the mechanism of inhibitory effect of procainamide on clonidine-induced platelet aggregation was to competitively antagonize activating alpha 2-receptors and others of clonidine on platelet membrane.
Department of Pharmacology, First Military Medical College, Guangzhou, China.
C W
CW
Shan
J W
JW
Yang
S Q
SQ
Yang
D000818:Animals; D001667:Binding, Competitive; D003000:Clonidine / Q000037:antagonists & inhibitors*; D008297:Male; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011342:Procainamide / Q000494:pharmacology*; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects
D010975:Platelet Aggregation Inhibitors; D011942:Receptors, Adrenergic, alpha; D011342:Procainamide; D003000:Clonidine