COMPARISON OF THE IN-VIVO EFFECTS OF MORPHINE AND METHADONE ON NATURAL-KILLER-CELL ACTIVITY IN SPLEEN, PERITONEAL-CAVITY, AND LUNGS IN RATS

Opiates and opioid agents are known to affect the immune system. In hu mans this includes alterations in natural killer (NK) cell activity. M orphine is reported to reduce in vivo spleen NK activity in rats, wher eas for methadone only in vitro data have been described. In the prese nt paper we describe a systematic study on the chronic effects of well -known opiates, comparing for the first time the effects of morphine a nd methadone on NK cell activity in various organs: in addition to spl een, also in the peritoneal cavity, and lungs. In all organs the NK ac tivity was determined using three effector: target cell ratios. Morphi ne and methadone given by food during 6 weeks decreased the NK cell ac tivity in rat spleen, supporting published data on morphine. The role of the opiate receptor is discussed. However, the overall action of mo rphine could not be described as suppressive because stimulation of NK cell activity in the peritoneal cavity and lungs by morphine was foun d. In contrast, methadone induced a decrease in the NK cell activity i n these organs. Apart from these differential expressions of morphine and methadone associated effects on NK cell activity, the findings dem onstrate the potential adverse effects of these opiates on an importan t antiviral defence mechanism. Copyright (C) 1996 International Societ y for Immunopharmacology