Effects of escapable and inescapable foot-shock on rat atrial beta-adrenoceptors.
The chronotropic responsiveness to norepinephrine (NE) and isoproterenol (ISO) was determined in right atria isolated from rats submitted to repeated escapable or inescapable foot-shock. Significant postjunctional supersensitivity to ISO, but not to NE, was observed in both groups. No significant change in the pA2 value of metoprolol (a selective beta 1-adrenoceptor antagonist) was detected. However, a decrease of the maximum response to soterenol, a partial agonist at beta 1-adrenoceptors, occurred only after inescapable foot-shock. The enhanced sensitivity to ISO was abolished by butoxamine (a selective beta 2-adrenoceptor antagonist) and accompanied by a marked increase in the pA2 value of this antagonist. We conclude that the ability to control the shock prevented the down-regulation of the pacemaker beta 1-adrenoceptors but not the increased participation of beta 2-adrenoceptors in the response of the rat sinoatrial node to catecholamines after repeated foot-shock.
Dep. Engenharia Biomédica, Faculdade de Engenharia Elétrica, Universidade Estadual de Campinas, Sao Paulo, Brazil.
R A
RA
Bassani
J W
JW
Bassani
D000818:Animals; D002078:Butoxamine / Q000494:pharmacology; D004597:Electroshock; D004983:Ethanolamines / Q000494:pharmacology; D006325:Heart Atria / Q000503:physiopathology; D006339:Heart Rate / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D016627:Oxidopamine; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D013315:Stress, Psychological / Q000503:physiopathology*; D013563:Sympathectomy, Chemical
D004983:Ethanolamines; D011943:Receptors, Adrenergic, beta; D002078:Butoxamine; D016627:Oxidopamine; C100252:soterenol; D008790:Metoprolol; D007545:Isoproterenol; D009638:Norepinephrine