Objectives : The purpose of present study is to investigate the influence of a spinal gamma-aminobutyric acid B (GABAB) receptor on a central regulation of blood pressure(BP) and heart rate(HR), and to define its mechanism in the spinal cord. Methods : In urethane-anesthetized, d-tubocurarine- paralyzed and artificially ventilated male Sprague-Dawley rats, intrathecal administration of drugs were carried out using injecton cannula(33-gauge stainless steel) through the guide cannula(PE 10) which was inserted intrathecally at lower thoracic level through the puncture of a atlantooccipital membrane. Results : Intrathecal injection of an GABAB receptor agonist baclofen(30, 60, 100 nmol) decreased both blood pressure and heart rate dose-dependently. Pretreatment with 8-bromo-cAMP(50 nmol), a cAMP analog or glipizide(50 nmol), a ATP-sensitive K+ channel blocker attenuated the depressor and bradycardic effects of baclofen (100 nmol) but not with 8-bromo-cGMP(50 nmol) a cGMP analog. Conclusions : The GABAB receptor in the spinal cord plays an inhibitory role in central cardiovascular regulation and that this depressor and bradycardic actions are mediated by the decrease of cAMP via the inhibition of adenylate cyclase and the opening of K+ channel.