The interaction of the enantiomers of carvedilol with alpha 1- and beta 1-adrenoceptors.
The stereoselectivity of carvedilol, a novel beta-adrenoceptor antagonist and vasodilator with one asymmetric carbon atom, was examined at alpha 1- and beta 1-adrenoceptors in vitro and in vivo. (-)-(S)-Carvedilol is a potent, competitive antagonist of the beta 1-adrenoceptor-mediated positive chronotropic response to isoproterenol in guinea pig atrium, with a dissociation constant (KB) of 0.4 nM. (+)-(R)-Carvedilol was more than 100-fold less potent than the (-)-S-enantiomer as an antagonist of beta 1-andrenoceptors, having a KB of approximately 45 nM. Consistent with these findings (-)-(S)-carvedilol (0.1 mg/kg, i.v.) produced a 25-fold rightward shift in the beta 1-adrenoceptor-mediated positive chronotropic response to isoproterenol in pithed rats, whereas the (+)-R-enantiomer had no beta 1-adrenoceptor blocking activity in vivo at this dose. In contrast to the marked degree of stereoselectivity observed at beta 1-adrenoceptors, both (-)-(S)- and (+)-(R)-carvedilol produced equal antagonism of the alpha 1-adrenoceptor-mediated vasoconstrictor response to norepinephrine in rabbit aorta, with KB values of 14 and 16 nM, respectively. Furthermore, in the pithed rat, the alpha 1-adrenoceptor-mediated pressor dose-response curve to cirazoline was shifted approximately 6-fold to the right by both the (+)-R- and (-)-S-enantiomers of carvedilol at a dose of 1 mg/kg, i.v. In anesthetized spontaneously hypertensive rats, (-)-(S)-carvedilol was 6-fold more potent as an antihypertensive than (+)-(R)-carvedilol.(ABSTRACT TRUNCATED AT 250 WORDS)
Nichols
A J
AJ
Department of Pharmacology, Smith Kline & French Laboratories, King of Prussia, Pennsylvania 19406.
Sulpizio
A C
AC
Ashton
D J
DJ
Hieble
J P
JP
Ruffolo
R R
RR
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000758:Anesthesia; D000818:Animals; D002227:Carbazoles / Q000494:pharmacology*; D000077261:Carvedilol; D003655:Decerebrate State; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats; D011918:Rats, Inbred SHR; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*; D013237:Stereoisomerism
D000319:Adrenergic beta-Antagonists; D002227:Carbazoles; D007093:Imidazoles; D011412:Propanolamines; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D000077261:Carvedilol; D007545:Isoproterenol; C014282:cirazoline; D009638:Norepinephrine