Systematic Oscillations of Amino Acid Transport in Liver from Rats Adapted to Controlled Feeding Schedules

Abstract

The model amino acid, cycloleucine, was used to study amino acid transport in the liver of rats fed ad libitum and rats adapted to 8 hours' feeding in either a 24-hour cycle or a 48-hour cycle under controlled lighting conditions. The rats were killed at various times in the cycle to determine whether oscillatory changes occurred in the amino acid transport system. Systematic oscillations of amino acid transport, with little individual variation, were observed in liver of rats adapted to controlled feeding and fasting periods. In contrast, no apparent oscillations and considerable individual variation were observed in amino acid transport in liver of rats fed ad libitum. The systematic oscillations of amino acid transport in liver appear to be related to the dietary state of the animal. Also, adrenal function contributed to a secondary oscillation observed during the early fasting period of the 48-hour cycle. The oscillations in the amino acid transport system of fasting-adapted rats correlate well with observed oscillations in the activity of liver tyrosine transaminase from the same rats.