Postnatal development of body mass and of hepatic xenobiotics biotransformation of male rats with low body mass at birth.

Body mass gain of male rats with low body mass at birth was lower from birth up to the 5th postnatal day, but higher from the days 5 to 30 in comparison with male litter mates with normal body mass at birth. Absolute body and liver masses were significantly lower up to the 30th postnatal day, but fully improved at adult age. No differences of ethoxycoumarin O-deethylation activities existed between both groups at all ages. Ethylmorphine N-demethylation activity was significantly lower in newborn males with low body mass, but had been fully developed as early as the 5th postnatal day. We conclude that postnatal adaptation of male rats with spontaneous growth retardation at birth is slightly delayed only during the first days of life.