Evidence that the positive inotropic effects of the alkylxanthines are not due to adenosine receptor blockade

Abstract

1 We investigated the possibility that the positive inotropic effects of the alkylxanthines are due to adenosine receptor blockade. 2 The potency of 8-phenyltheophylline, theophylline and enprofylline as adenosine antagonists was assessed in vitro, using the guinea-pig isolated atrium, and in vivo, using the anaesthetized dog. 3 The order of potency of the alkylxanthines as antagonists of the negative inotropic response to 2-chloroadenosine in vitro, and of the hypotensive response to adenosine in vivo was 8-phenyltheophylline > theophylline > enprofylline. 4 The order of potency of the alkylxanthines as positive inotropic and chronotropic agents in the anaesthetized dog was enprofylline > theophylline > 8-phenyltheophylline. 5 The results of this study indicate that the inotropic effects of the alkylxanthines in the anaesthetized dog are not due to adenosine receptor blockade.