The ontogeny of plasma osmolality and intravascular volume maintenance during short-term starvation in rats.

Body fluid deviations were examined in albino rats of both genders between 30 and 100 days of age during food deprivation. Plasma volume declined with age in free-feeding control groups. Hypovolemia induced by starvation (4 days) was more intense in 30- to 60-day-old animals than in 80- and 100-day groups. Plasma ismolality concentration of control groups indicated increases with age leveling off after 60 days. The initiation of drinking during fasting was accompanied by physiologically significant elevations in plasma osmolality over ad libitum concentrations at each age tested. In a second experiment, repeated exposure to short periods of food deprivation (2 days) during development resulted in the maintenance of intravascular fluid at control volumes. Longer periods (4 days) of deprivation did not result in savings of intravascular volume loss evidenced during starvation. These results suggest that rats compensate for hypovolemia induced by short-term starvation when provided experience with food restriction during development.