Gender differences in blood levels, but not brain levels, of ethanol in rats

Female rodents tend to drink more alcohol than males, a difference that eme rges at puberty and appears to vary over the female estrous cycle. In addit ion, male and female rodents display different responses to alcohol; for ex ample, female rats are reported to have faster elimination rates than males . We were interested in whether circulating ovarian hormones influence alco hol distribution to or elimination from the brain of rats, which might expl ain observed differences in drinking behavior. We administered 0.8 g/kg of ethanol via intraperitoneal injection to age-matched male and female Spragu e-Dawley rats. Extracellular brain ethanol was sampled using microdialysis, and vascular ethanol concentrations were determined via tail blood collect ion, in two separate experiments. Ethanol pharmacokinetic parameters were c alculated for both compartments. There were no differences in pharmacokinet ic parameters due to gender or estrous cycle stage in brain ethanol concent ration profiles. There were, however, differences in blood ethanol profiles : females showed faster elimination rates and a smaller area under the etha nol concentration versus time curve than males. In addition, the maximum co ncentration varied significantly across Be estrous cycle. These results sug gest that (1) circulating ovarian hormones do not influence alcohol distrib ution to the brain, but do influence distribution to more peripheral tissue s such as the tail; and (2) apparent differences in tail blood alcohol leve ls may not reflect differences in brain levels.