POTENTIAL ROLE OF THE AUTONOMIC NERVOUS-SYSTEM IN THE IMMUNOSUPPRESSIVE EFFECTS OF ACUTE MORPHINE ADMINISTRATION

These studies investigated the role of the autonomic nervous system in mediating the immunosuppressive effect of morphine on blood lymphocyt e proliferation in rats. To determine the contribution of the autonomi c nervous system, rats were pretreated with the ganglionic blocker chl orisondamine (5 mg/kg) prior to morphine (7 mg/kg) administration. Gan glionic blockade with chlorisondamine completely antagonized the inhib itory actions of morphine, suggesting that intact ganglionic transmiss ion was required for the inhibition to occur. Blockade of postganglion ic parasympathetic neurotransmission with atropine methylbromide (1 mg /kg) or blockade of sympathetic neurotransmission with the alpha-adren oceptor antagonist phentolamine (1 mg/kg) did not attenuate the suppre ssive effect of morphine. Blockade of beta-adrenoceptors with proprano lol (2.5 mg/kg) resulted in partial antagonism, but this action was no t shared by the peripherally acting beta-adrenoceptor antagonist nadol ol (6 mg/kg). These results suggest that the inhibitory effect of morp hine on blood lymphocyte proliferation may be mediated through activat ion of the autonomic nervous system; however, individual blockade of e ither the parasympathetic or sympathetic division of the autonomic ner vous system was not sufficient to antagonize this immunosuppressive ef fect.