EFFECTS OF MILK CONSUMPTION AND DEPRIVATION ON BODY-FLUIDS OF SUCKLING RATS

Ten-day-old rats were separated from their mothers for 4 hours, allowed to suckle, and then separated immediately after this nursing bout. Plasma protein concentrations started to fall from deprivation levels by the end of the nursing bout, continued to decline for 30 min, and then gradually returned to deprivation levels 3 1 2 hours later. Plasma sodium concentrations showed similar fluctuations after nursing, but these were not as rapid or reliable as those in plasma protein. Urine production increased steadily after suckling and by 4 hours after was highly correlated with milk intake during the nursing bout, indicating a relatively rapid disposal of excess fluids obtained from milk. Plasma volume (as measured by plasma protein or hematocrit) in pups kept at 30° or 35°C decreased by 4.6 or 8.3% within 2 hours following separation from the mother. Pups separated and kept at 35°C showed greater increases over time in plasma protein, urine production and weight loss than those kept at 30°C. The results indicated that body fluids, and particularly plasma volume, are highly labile in suckling rats; intravascular fluid volume decreases in a short time during the mother's absence, is restored quickly by nursing, only to fall again since the impact of milk consumption dissipates rapidly. © 1979.