Figure 8. (A) Halothane-induced vasoconstriction and (B) relaxation of KCl-constricted and (C) phenylephrine-constricted mesenteric resistance arteries after endothelial denudation. The concentration-response relationships for the (D) vasoconstricting effect and (E) vasorelaxing effect in KCl-constricted vessels and (F) phenylephrine-constricted vessels are displayed (plus/minus SEM) with fits to Hill equations (solid lines). The concentration-response relationships (D-F) observed in the denuded vessels (open symbols) and in the intact vessels (solid symbols) were similar. In denuded and intact vessels, the fits yielded EC⁵⁰values of (D) 0.81 mM (n = 3) and 0.48 mM (n = 8), respectively, for the vasoconstricting effect;(E) 0.52 mM (n = 3) and 0.36 mM (n = 3), respectively, for the relaxing effect on KCl-constricted vessels; and (F) 0.67 mM (n = 3) and 0.75 mM (n = 5), respectively, for the relaxing effect on phenylephrine-constricted vessels. The open triangles and closed triangles are shown for reference on the x-axis in F to denote [nearly equal] 1 MAC (0.3 mM) and [nearly equal] 2 MAC (0.6 mM), respectively.