Development in the Newborn Rat of the Conjugation and De-conjugation Processes Involved in the Enterohepatic Circulation of Diethylstilboestrol

Abstract

1. The biological half-life in rats of unconjugated material after intraperitoneal administration of [¹⁴C]diethylstilboestrol decreased from 131 min on the day of birth to 14 min in 25 day-old animals. The rate of conjugation of diethylstilboestrol reached an adult level by the 25th day after birth. 2. Newborn rats apparently had a slower rate of excretion of conjugates of diethylstilboestrol and its metabolites in the bile. 3. Intestinal hydrolysis of diethylstilboestrol conjugates was minimal on the day of birth and at 5 days old, and was not fully developed until the third to fourth week after birth. 4. Enterohepatic circulation of diethylstilboestrol developed during the first month after birth; thus the newborn may be spared from reabsorption of unconjugated drug and metabolites during a time when the enzymes required for drug conjugation are still developing.