Immediate acceptance of ethanol in infant rats: ontogenetic differences with moderate but not high ethanol concentration.

Abstract

During the preweanling period, infant rats consume large quantities of ethanol without initiating procedures. Ethanol intake during this period has seemed to be age related, with peak consumption occurring near the end of the second postnatal week, on postnatal day (P)12, but only a narrow range of conditions has been tested. Independent ingestion of ethanol was measured at each of two ages, P12 and P18, with systematic variation in ethanol concentration, duration of exposure, and mode of fluid presentation. Ethanol ingestion was measured in terms of percentage body weight gain, grams of absolute ethanol ingested per unit body weight, and blood ethanol concentration. Ingestion of 30% ethanol during a 40-min period led to blood ethanol concentrations approaching 300 mg/100 ml at both P12 and P18. For ethanol concentrations of 10 or 20%, ingestion at P12 was greater than at P18. When ethanol was available from ethanol-soaked Kimwipe on the floor, ethanol intake transdermally or by inhalation was apparent but accounted for less than half of the overall ethanol intake. It was clear that for older infants, which are susceptible to ethanol's diuretic effects and are much more likely to self-void than those at P12, measurement of intake by percentage body weight gain can underestimate ethanol ingestion. The infant rat ingests extraordinarily high levels of ethanol, in concentrations as high as 30%, without initiation procedures. Acceptance of ethanol by infants on first exposure contrasts with the conventional rejection of these concentrations by adults. It is unclear why younger infants (P12) consume more 10 and 20% ethanol than older (P18) infants. These and other differences in ethanol intake between infants and older animals may be due initially to the relative ontogeny of receptors for bitter and sweet taste and subsequently to other factors.