This study was carried out in order to clarify whether the cardiovascular effect of prostaglandin(PG) F_2α might be centrally mediated. In unrestrained conscious rat, PGE_2α was administered into the lateral ventricle. The mechanism of action was also studied by observing the interaction with several adrenergic antagonists injected subcutaneously, Indomethacin was administered into lateral ventricle to investigate the role of endogenous PGE_2α on the central regulation of cardiovascular system. The results were as follows: 1) The intraventricular injection of PGE_2α produced an increase in blood pressure and heart rate. 2) The pretreatment with phenoxybenzamine (2 mg/g, s.c.) inhited pressor, but not heart rate responses to the intraventricular injection of PGE_2α (2μg/kg). 3) The pretreatment with propranolol (1 mg/kg, s.c.) inhibited tachycardia, but not pressor responses to the intraventricular injection of PGE_2α(2μg/kg). 4) The intraventricular injection of indomethacin (40μg/kg) could not induce significant changes in blood preesure and heart rate. 5) The result indicates that intraventricular injection of PGE_2α produces pressor and tachycardia responses in the unanesthetized rat, and it is mediated primarily by centrally increased sympathetic outflow. But the endogenous PGE_2α synthetized in the brain seems to play minor role in the direct regulation of cardiovascular system.