The present investigation was conducted to evaluate the effects of estradiol on ethanol-induced alterations of β-endorphin (β-EN) and met-enkephalin (ME) levels in specific brain regions of ovariectomized rats. Female Sprague-Dawley rats (100-124 g) adapted to a 12-hour light, 12-hour dark illumination cycle were used in these studies. Animals were ovariectomized under pentobarbital anesthesia. After a recovery period of 14 days, ethanol (3 g/kg as 22.5% solution in saline, i.p.), estradiol (50 µg/kg in 0.2 ml of olive oil, s.c. in the dorsal neck region), or a combination of ethanol and estradiol were administered to rats at 11:00 h. Control animals were injected intraperitoneally with 2 ml saline and subcutaneously with 0.2 ml olive oil. Animals were sacrificed by decapitation 2 h later. The brains were immediately removed; the cortex, hippocampus, hypothalamus, and midbrain were dissected and their β-EN and ME levels were measured by radioimmunoassay. Ethanol administration significantly decreased both β-EN and ME levels in the hypothalamus. Administration of estradiol alone also resulted in a significant decrease in β-EN and ME levels in the hypothalamus. Additionally, concurrent administration of ethanol and estradiol showed a decrease in the levels of β-EN and ME in the hypothalamus. Co-administration of ethanol with estradiol also caused a significant decrease in the levels of β-EN in midbrain. However, ME levels were increased in the midbrain after concurrent administration of estradiol and ethanol. ME levels also increased in the hippocampus and cortex after co-administration of estrogen and ethanol. These results clearly indicate that estradiol significantly alters ethanol-induced effects on β-EN and ME levels in specific brain regions of ovariectomized rats. The present findings may in part explain sex differences in alcohol effects.

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