The choice of opioid receptor subtype in isolated preparations by ohmefentanyl

Ohmefentanyl has significant inhibitory actions on the electrically evoked contractions of guinea pig ileum and mouse vas deferens. Their IC50 values are 0.15 nM and 0.89 nM, respectively. In the guinea pig ileum and the mouse vas deferens, both mu-antagonist naloxone and (mu + kappa)-antagonist Mr. 2266 antagonize readily the agonist action of ohmefentanyl, indicating that ohmefentanyl acts on mu-receptors in the guinea pig ileum and the mouse vas deferens. Like other mu-agonists, ohmefentanyl has agonist activity but no antagonist action in the rat vas deferens. In the rabbit vas deferens, the activity of ohmefentanyl is very weak. The IC50 value is 149 nM. These results further indicate that ohmefentanyl is a potent and selective mu-agonist.