Fig. 4. Effect of fentanyl on acetylcholine dose–response curve in rings pretreated with 10−7m pirenzepine. Fentanyl, 0.785 × 10−6m, attenuated (* P < 0.05 vs. 10−7m pirenzepine) acetylcholine-induced vasorelaxation compared with rings pretreated with 10−7m pirenzepine alone. PE = phenylephrine.
