Effect of naloxone on the sensitivity of the vas deferens to various agonists

The effect of naloxone in vitro, on noradrenaline (NA)-induced responses in guinea-pig isolated vas deferens was studied. The responses of NA were potentiated by naloxone (3 microM). It potentiated the responses to methoxamine which has least affinity for uptake sites. Responses induced by acetylcholine and potassium chloride were also potentiated by naloxone. Low calcium (0.8 mM) in the medium antagonized the potentiating action of naloxone. It is suggested that naloxone produces non-specific potentiation, by promoting calcium influx at the post-synaptic site.