Differential changes in lymphocyte beta 2-adrenoceptor density by beta-blocker administration: role of intrinsic sympathomimetic activity.
To study the role of intrinsic sympathomimetic activity (ISA) in beta-blocker-induced changes of beta-adrenoceptors, the effects of administration of several beta-blockers for 9 days on lymphocyte beta 2-adrenoceptor density--assessed by 125iodocyanopindolol binding--were investigated in 47 normotensive volunteers. Propranolol (unselective; no ISA; 4 X 40 mg/day) increased beta 2-adrenoceptor density by 25-40%; after withdrawal beta 2-adrenoceptor density declined slowly, being still elevated for 3 days. In contrast, the unselective beta-blockers pindolol (ISA (isoprenaline = 1.0) = 0.39; 2 X 5 mg/day) and mepindolol (ISA = 0.27; 2 X 5 mg/day) decreased beta 2-adrenoceptor density by 50% and 35%, respectively, while alprenolol with weak ISA (=0.066; 4 X 100 mg/day) had no effect. Among the beta 1-selective blockers studied, celiprolol with ISA (=0.32; 1 X 200 mg/day) decreased beta 2-adrenoceptor density by 30% whereas bisoprolol without ISA (1 X 10 mg/day) had no effect. It is concluded that the ISA determines the direction and amount of beta-adrenoceptor alterations induced by beta-blockers. Furthermore, changes in human lymphocyte beta-adrenoceptors reflect subtype-selective changes in beta 2-adrenoceptors, since the beta 1-selective blocker bisoprolol without ISA--in contrast to propranolol--did not affect lymphocyte beta 2-adrenoceptors. Accordingly, the fact that the beta 1-selective blocker celiprolol with ISA decreased lymphocyte beta 2-adrenoceptors, is consistent with the hypothesis that celiprolol possesses in addition to its beta 1-antagonistic activity a beta 2-agonistic activity.
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D005260:Female; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008214:Lymphocytes / Q000032:analysis* / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D010869:Pindolol / Q000031:analogs & derivatives / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000032:analysis; D013566:Sympathomimetics / Q000494:pharmacology*
D000319:Adrenergic beta-Antagonists; D011943:Receptors, Adrenergic, beta; D013566:Sympathomimetics; C015340:mepindolol; D011433:Propranolol; D010869:Pindolol; D007545:Isoproterenol