The effects of chronic morphine administration to mice on the contractile activity in vitro of the vas deferens without and with morphine.

Chronic treatment of mice with morphine enhances maximal responses to noradrenaline in isolated vasa deferentia. Addition of morphine to the bath further increases the responses to noradrenaline (facilitatory effect). Vasa deferentia from reserpine-pretreated mice showed increased responses to noradrenaline, but upon addition of morphine to the bath no further facilitatory response to noradrenaline. The facilitatory response was not inhibited by naloxone and it was not elicited by narcotic analgesics other than morphine. High calcium in the medium (3.8 mM) suppressed the enhanced maximal responses to noradrenaline of vasa deferentia from mice chronically treated with morphine and also suppressed the facilitatory response to noradrenaline. Low calcium in the medium (1.43 mM) had the opposite effects. Reserpine-induced changes of noradrenaline responses were not affected by alteration of the calcium concentration in the medium. In the K-depolarized vas deferens, a reduction of the depressant effect of morphine on the calcium-induced contractions was observed after chronic administration of morphine.