Endothelin-1, a 21 amino acid peptide originally isolated from porcine endothelial cells, has been reported to contract arteries and veins from several mammalian species. We studied the effect of endothelin-1 on blood vessels removed from turtle (Pseudymes scripta), frog (Rana pipiens), and catfish (Amiurus melas). The vessels were suspended for isometric recording in thermally controlled organ baths and were exposed cumulatively to endothelin-1 (0.5-100 nM). All vessels showed a concentration-dependent increase in isometric force. The half-maximal concentrations (EC50) of endothelin-1 were all in the nanomolar range: turtle left systemic arch (17.9 +/- 1.2 nM), frog systemic arch (5.5 +/- 1.1 nM), catfish mesenteric artery (6.3 +/- 1.3 nM), and catfish posterior cardinal vein (2.5 +/- 1.4 nM). Vessels from frog and catfish developed more tension when exposed to 100 nM endothelin-1 than to 80 mM KCl (ET/KCl tension ratio). Our observations that endothelin-1 potently contracts blood vessels from reptiles, amphibians, and fish suggest that endothelin-1 may be a vertebrate peptide that has been conserved during evolution.