Effect of leucine enkephalin on ethanol produced behavioral depression in the mouse

The effect of leucine enkephalin (LNK) on spontaneous locomotor activity was studied in mice of both sexes. The effect of a depressant dose of ethanol (ET) on LNK-mediated response on motility was also studied. In addition, the determination of specific activities of the hepatic enzymes primarily involved in the metabolism of ET and acetaldehyde was studied. Lactate dehydrogenase (LDH) isoenzymes were also assayed in both plasma and heart tissues. Intraperitoneal injection of LNK, 100 mg/kg, exerted behavioral depression in the male but not female mouse compared to controls. This effect was apparent for the initial 30 min posttreatment. Injection of two smaller doses of LNK, which were devoid of effect on mouse motility, prior to a depressant dose of ET counteracted ET-caused depression of motility only in the female mouse. This became apparent 30 min postdrug injection and lasted for 60 min thereafter. The LNK and ET treatment inhibited only male mouse liver aldehyde dehydrogenase in both cytoplasmic and mitochondrial preparations concomitant with reduction of plasma but not heart LDH1 isoenzyme from corresponding controls. The results suggest that LNK and ET affect different systems involved in behavioral depression tested and show a potential for LNK in antagonizing the ET effect studied. The data also indicate a sex-dependent effect of LNK on motility and of its interaction with ethanol on the enzymes studied.