MORPHINE-INDUCED DECREASES IN IN-VIVO ANTIBODY-RESPONSES

Endogenous opioids have been shown to be released during acute stress and could play a role in immune modulation and activation of the hypot halamo-pituitary-adrenal axis. We investigated the ability of morphine sulfate to mimic stressor effects on decreases in in vivo antibody re sponses. Sprague-Dawley and Fischer 344 rats were given an intraperito neal injection of an antigen, Keyhole limpet hemocyanin (KLH), followe d by a single intravenous injection of either saline or varying doses of morphine sulfate. The corticosterone and anti-KLH IgG antibody resp onses to morphine were measured. A dose-dependent increase in corticos terone was observed. Significantly lower levels of anti-KLH IgG antibo dies were observed in morphine-treated animals but these effects were strain and dose dependent. In Sprague-Dawley rats, 3 and 10 mg/kg dose s of morphine decreased antibody levels while 1.5, 5, and 15 mg/kg did not change antibody responses. In Fischer 344 rats a dose of 5 mg/kg of morphine decreased antibody levels while 10 and 15 mg/kg did not ch ange antibody responses. These results indicate that morphine can decr ease antibody levels and that these decreases are not correlated with elevated levels of corticosterone. To determine if opioid binding is c ritical to these changes, animals received naltrexone prior to the adm inistration of morphine. Naltrexone partially attenuated corticosteron e levels, but completely blocked morphine-induced changes in immune fu nction. (C) 1994 Academic Press, Inc.