VITAMIN-A STATUS IN RATS SUBMITTED TO GRADED-LEVELS OF DIETARY RESTRICTION

Studies on aging mice have shown that dietary restriction (DR) may influence retinoid absorption (1) and recent investigations from our laboratory demonstrated increased tissue levels of retinoids in old rats submitted to DR (2). To better understand the effect of DR on retinoid metabolism we measured retinoid content by HPLC in plasma, liver, kidney, lungs, intestine, adipose tissue and mammary glands of 8 months old-rats submitted to diets providing 10, 20, 30 and 40% less energy than ad Libitum-fed rats. We observed a significant decrease in plasma retinol levels proportional to the degree of DR while liver concentrations of total retinoids remained unchanged. However, the ratio of retinol/retinyl esters (RE) was significantly higher in liver of DR groups. The distribution of various RE in the liver was found to be significantly altered between the control and the DR groups. Kidney retinoid levels were slightly but significantly decreased while lungs retinoid levels were markedly reduced in DR rats. Retinoid concentrations in intestine, adipose tissue and mammary glands were not influenced by DR. Plasma TTR levels measured at the end of the study were not modified in DR rats. These results demonstrate that DR alters retinoid metabolism in 8 months-old rats but do not increase liver content of vitamin A at this age. The fact that plasma retinol was decreased despite normal concentrations in liver suggests that REP synthesis or release from the liver may be altered.