Mediation of the cardiovascular response to spinal γ-aminobutyric acid(B) receptor stimulation by adenosine A₁ receptors in anesthetized rats

Cardiovascular inhibitory effects induced by intrathecal (i.t.) administration of adenosine A₁ receptor agonist and its modulation by γ-aminobutyric acid(B) (GABA(B)) receptor was suggested by our previous report. In this experiment, we examined the mediation of cardiovascular effects of GABA(B) receptor stimulation by adenosine A₁ and A₂ in the spinal cord. I.t. administration of GABA(B) receptor agonist, baclofen (30, 60 and 100 nmol) produced a dose dependent decrease of blood pressure and heart rate. Pretreatment with adenosine A₁ receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine (50 nmol), attenuated the depressor and bradycardiac effects of baclofen (100 nmol), but not with adenosine A₂ receptor antagonist, 3,7-dimethyl-1-propargylxanthine (25 nmol). These results suggest that GABA(B) receptors in the spinal cord play an inhibitory role in the central cardiovascular regulation and that the depressor and bradycardiac actions are mediated by adenosine A₁ receptors. (C) 2000 Elsevier Science Ireland Ltd.