Fatty acid utilization during development of the rat.

1. In the absence of added carnitine pronounced changes occur during development, in the degradation of [U-(14)C]palmitate to (14)C-labelled acid-soluble material (predominantly ketone bodies) and (14)CO(2) by liver homogenates. The formation of both products by liver homogenates of 5-day-old rats is considerably higher than in foetal livers. This high value is maintained during the suckling period and falls after weaning to adult values which are similar to those of the foetus. Addition of carnitine stimulates production of acid-soluble material throughout development. The effect of added carnitine on CO(2) production varies with age, stimulating in foetal and post-weaning age groups but inhibiting during the suckling period. 2. The degradation of [U-(14)C]palmitate to acid-soluble material and CO(2) by heart homogenates also varies during development. Formation of both products is highest 5 days after birth and thereafter decreases steadily to adult values. Addition of carnitine stimulates the production of both CO(2) and acid-soluble material at all ages. 3. The activity of carnitine palmitoyltransferase in liver increased after birth to reach maximum activity at 2-5 days of age. Thereafter the activity of the enzyme decreased until day 15 of life and then remained constant until day 30, decreasing after this time to adult values which were about one half of the foetal liver activities.