Body water content, ethanol pharmacokinetics, and the responsiveness to ethanol in young and old rats

Total body water was determined by desiccation of samples of 6 young (5-7 months) and 6 old (24-26 months) female CD strain rats and was observed to contribute 58.8 +/- 1.4 and 45.8 +/- 1.7% to the total body mass of the respective groups. The values obtained were used to construct an equation (linear regression: body weight vs. percent body water) with which to estimate the body water content of living subjects (n = 10 each) of the same populations, using body weight as the predictive variable. Doses of ethanol estimated to produce similar drug concentrations in the body water compartments were administered to old and young subjects and were observed to produce similar blood ethanol disappearance curves in both groups of rats. The regional brain concentrations of ethanol were found to be highest in the pons-medulla and lowest in the midbrain. On a region-by-region basis the values obtained for young rats were observed to more closely approximate the concentrations of ethanol in the neck blood than were the values obtained from the analysis of brain tissue from old rats. Old and young subjects dosed on the basis of predicted equivalent dilution of ethanol in body water did not differ noticeably in their response to ethanol hypothermia.