Relationship between desensitization and downregulation of beta-adrenoceptors in cardiac tissues after prolonged in vivo infusion of T-0509, a beta 1-adrenoceptor agonist.
Jpn J Pharmacol
; 73(4): 325-32, 1997 Apr.
Article
em En
| MEDLINE
| ID: mdl-9165369
ABSTRACT
To examine the contribution of beta-adrenoceptor (beta AR) downregulation to desensitization of beta ARs by chronic administration of a beta AR agonist, we compared the adenylyl cyclase (AC) activities in two kinds of cardiac ventricular membranes with decreased available beta ARs one was derived from rats infused with a selective beta 1 AR agonist, T-0509 [(-)-(R)-1-(3,4-dihydroxyphenyl)- 2-[(3,4-dimethoxyphenethyl)-amino]ethanol hydrochloride], in vivo (40 micrograms/kg/hr, s.c. for 6 days); and the other was obtained from treatment of control membranes with an irreversible beta AR antagonist, bromoacetyl alprenolol methane (BAAM). T-0509 infusion decreased the densities of beta 1 ARs and beta 2 ARs by 26% and 32%, respectively, and reduced the maximal isoproterenol-stimulated AC activity by 53%. The amount of Gs alpha and Gi alpha proteins in the membranes was not significantly changed by T-0509 infusion. To make preparations that mimic the T-0509-induced downregulation, we treated the control membranes with 100 nM BAAM in vitro. The BAAM treatment decreased the Bmax value of [125I]iodocyanopindolol for beta 1 ARs and beta 2 ARs by 29% and 36%, respectively, whereas it reduced the maximal effect of isoproterenol on AC activity only by 37%. These results suggest that downregulation of beta ARs cannot fully account for the desensitization by chronic treatment of T-0509 and that other mechanism(s) can play a significant role in the loss of responsiveness.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Receptores Adrenérgicos beta 2
/
Agonistas Adrenérgicos beta
/
Antagonistas Adrenérgicos beta
/
Etanolaminas
/
Alprenolol
/
Miocárdio
Limite:
Animals
Idioma:
En
Revista:
Jpn J Pharmacol
Ano de publicação:
1997
Tipo de documento:
Article
País de afiliação:
Japão