Depression of Hepatic Glutathione by Opioid Analgesic Drugs in Mice

The ability of morphine and other opioid analgesic drugs to diminish hepatocellular glutathione (GSH) concentrations was examined in ICR mice. When administered intraperitoneally, morphine, hydromorphone, ethylmorphine, l-alpha-acetylmethadol (LAAM), and meperidine all caused a significant decrease in hepatic GSH concentrations in male mice while codeine, methadone, butorphanol, nalbuphine, and pentazocine were without effect even at doses up to those approaching acute lethality. Depression of hepatic GSH equivalent to that observed after ip administration could be elicited by icv administration of small doses of morphine, ethylmorphine, and hydromorphone. LAAM and meperidine were ineffective following icv administration in these experiments. The discrepancy between results following ip versus icv administration of LAAM and meperidine suggests that hepatic metabolism of some opioids may be important for their activity in the CNS, as both norLAAM and normeperidine diminished hepatic GSH when administered by the icv route. The opioid-induced lowering of hepatic GSH does not appear to be sex-dependent since morphine and LAAM produced qualitatively and quantitatively similar effects on hepatic GSH in female mice. Morphine administered icv produced a substantial increase in the hepatotoxicity of two compounds dependent upon GSH for detoxification, acetaminophen and cocaine, as measured by serum alanine aminotransferase activities. These observations indicate that a number of opioid analgesic drugs have the potential to diminish hepatic GSH. Further, these results support earlier studies which indicate that central opioid effects on hepatic GSH are mediated through mu-opioid receptor stimulation. Last, these studies suggest that a centrally initiated opioid action on hepatic GSH may significantly influence the susceptibility of the liver to the effects of some hepatotoxic agents.