Thiopentone inhibits beta-adrenergic in myocardial

The purpose of this study was to determine the importance of inhibition of beta-adrenergic function in thiopentone-induced myocardial depression. Using an isolated, electrically stimulated rat left atria model, contractile dose-response curves to thiopentone (200 uM, 400 t~M, 600 #M, 800 t~M) were shifted to the right in preparations treated with 10 -3 M dibutyryl cyclic adenosine monophosphate (cAMP) compared with atria stimulated with 10 -6 M isoprenaline, demonstrating that inhibition of beta-adrenergic mechanisms by thiopentone is physiologically important. Depression by thiopentone was similar in atria treated with 10 -5 M forskolin compared with preparations stimulated with 10 -6 M isoprenaline, indicating that thiopentone does not block beta-adrenergic receptors. It is concluded that thiopentone depresses myocardial function by several mechanisms, one of which involves inhibition of the adenyl cyclase cascade. The adenyl cyclase enzyme is a likely site where thiopentone inhibits the system; however, other components of the cascade may also be involved. L'objectif de cette &ude consiste it d&erminer l'influence de l'inhibition de l'activit$ fl-adr~nergique sur la d~pression myocardique induite par le thiopentone. A l'aide d'un modble constitu~ d'une oreillette gauche de rat stimulde dlectriquement, la relation dose-effet du thiopentone sur la contractilit$ (200 t~M, 400 t~M, 600 #M, 800 ~M) se d@lace vers la droite dans des pr@arations trait~es avec de l'addnosine monophosphorique cyclique (cAMP) 10 -3 M comparativement it des oreillettes stimuldes avec de l~sopr~naline 10 -6 M, ce qui d~montre que