1. Intrathecal (i.t.) injection of baclofen (30, 60 and 100 nmol), a GABA(B) receptor agonist, produced a dose-dependent decrease in blood pressure (BP) and heart rate (HR). 2. Pretreatment with 5-aminovaleric acid (50 nmol), a GABA(B) receptor antagonist, blocked the depressor and bradycardic effects of baclofen (100 nmol). 3. Pretreatment with 8-bromo-cAMP (10 nmol), a cAMP analogue, attenuated the depressor and bradycardic effects of baclofen (100 nmol), but not with 8-bromo-cGMP (10 nmol), a cGMP analogue. 4. In addition, pretreatment with glipizide (20 nmol), an ATP-sensitive K+ channel (K(ATP)) blocker, attenuated the depressor and bradycardic effects of baclofen (100 nmol). These results suggest that GABA(B) receptors in the spinal cord have an inhibitory role in the central cardiovascular regulation and that these depressive and bradycardic actions are modified by cAMP and by K(ATP) channel blockade.