Fig. 1. Effects of increasing concentration of serotonin (5-HT; A), endothelin-1 (ET-1; B) and noradrenaline (NA; C), on the relative tension of alligator intrapulmonary arteries. The effects of NA were evaluated on relaxed vessels as well as vessels preconstricted with ET-1 (10^–8 mol l^–1) before and after incubation with propranolol (10^–5 mol l^–1). Contraction is expressed relative to the contraction induced by 60 mmol l^–1 KPSS and relaxation is given as a percentage of the precontraction. Values are means ± s.e.m.; each dose–response relationship is based on six blood vessels from six different animals, using a total of 13 alligators. An asterisk indicates a significant difference (P<0.05) from control values evaluated by a one-way ANOVA for repeated measures or a two-way ANOVA followed by Dunnett's post hoc test.