Supersensitivity to noradrenaline in vas deferens from morphine-dependent mice is confirmed.

Vasa deferentia isolated from morphine-treated mice were subsensitive (tolerant) to the inhibitory effect of morphine on field stimulation-induced contractions (4.1 fold at the IC50 level) and exhibited supersensitivity to exogenously added noradrenaline. The magnitude of the supersensitivity to noradrenaline was not affected by the absence (2.6 fold) or presence (2.9 fold) of morphine in the bathing medium thus ruling out, as previously suggested, that the absence of morphine in the bathing solution could induce an 'in vitro morphine withdrawal'. Addition of naloxone to such vasa deferentia increased the maximum response to noradrenaline without a significant change of the sensitivity to the neurotransmitter. It is concluded that isolated morphine-tolerant vasa deferentia exhibit supersensitivity to exogenously added noradrenaline. Naloxone added in vitro to such vasa deferentia enhanced the maximum response to noradrenaline.