The effects of endothelin-1 (ET-1) administered i.v. or intracerebroventricularly (i.c.v.) on arterial pressure (MAP), heart rate and cardiac output were studied in the conscious rat. Systemic injection of ET-1 (0.1 to 1 nmol/kg i.v.) increased dose-dependently MAP and decreased heart rate. The doses of 0.3 and 1 nmol/kg produced initially transient hypotension and tachycardia which were accompanied by a decrease in total peripheral resistance index (TPRI). Cardiac output was significantly reduced and TPRI increased during the pressor response to 0.3 and 1 nmol/kg ET-1. ET-1 i.c.v. (30 pmol/kg) produced a profound pressor and vasoconstrictor response which was followed by cardiovascular collapse and death within 20 min after i.c.v. injection. Low doses (1 to 10 pmol/kg) of ET-1 i.c.v. had no effect on the cardiovascular system. The present data are in accordance with the studies demonstrating biphasic blood pressure and heart rate responses to i.v. ET-1 in the rat. Profound cardiac depressor and peripheral vasoconstrictor responses were found to accompany the pressor phase. Our results also showed for the first time direct central pressor and vasoconstrictor effects of ET-1 insinuating that endothelin might be a neuropeptide participating in the central cardiovascular control.