This study was carried out in order to clarify whether the cardiovascular effect of prostaglandin(PG) F<sub>2α</sub> might be centrally mediated. In unrestrained conscious rat, PGE<sub>2α</sub> 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<sub>2α</sub> on the central regulation of cardiovascular system. The results were as follows: 1) The intraventricular injection of PGE<sub>2α</sub> 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<sub>2α</sub> (2μg/kg). 3) The pretreatment with propranolol (1 mg/kg, s.c.) inhibited tachycardia, but not pressor responses to the intraventricular injection of PGE<sub>2α</sub>(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<sub>2α</sub> produces pressor and tachycardia responses in the unanesthetized rat, and it is mediated primarily by centrally increased sympathetic outflow. But the endogenous PGE<sub>2α</sub> synthetized in the brain seems to play minor role in the direct regulation of cardiovascular system.