Body and organ growth in the newborn rat.

Body and organ growth were described in rat pups 1 h and 10 days of age. Several organs (e.g., brain and pineal gland) exhibited significant growth in 1-hour-old but not in 10-day-old rats. Further, organs such as the testis and liver showed significant growth in 10-day-old but not 1-hour-old pups. 11 h of exposure to a warming oven, devoid of maternal and nutritional input, significantly influenced the body and organ growth of both newborn and 10-day-old pups. These data show that the first 12 h of life is an active period of growth for the rat.