Central and peripheral administration of endothelin-1 induces an increase in blood pressure in conscious trout

The central and peripheral cardiovascular effects of endothelin (ET)-1 and ET-3 were investigated in conscious rainbow trout. Both intracerebroventricular and intra-arterial injections of ET-1 (6.25-25 pmol) but not ET-3 (25 pmol) caused a dose-dependent increase in mean dorsal aortic blood pressure and a concomitant decrease in heart rate. The hypertensive effects induced by intra-arterial and intracerebroventricular injection of ET-1 were associated with a significant (P < 0.05) increase in systemic vascular resistance. Intracerebroventricular inject-ion of ET-1 induced a twofold higher presser response than that caused by intra-arterial injection of ET-1 and provoked a barostatic gain that was reduced by 2.5- to a-fold compared with that calculated after intra-arterial administration of the peptide. The ET receptor antagonist bosentan significantly (P < 0.05) attenuated these responses regardless of the route of administration. Finally, intraarterial injection of ET-1 did not significantly modify plasma cortisol level. The present data demonstrate that intracerebroventricular and intra-arterial administration of very low doses of ET-1 produces hypertension in conscious trout. The lack of effect of ET-3 indicates that the hemodynamic actions of ET-1 are mediated both centrally and peripherally through ETA receptors.