LYMPHATIC ABSORPTION OF RETINOL IN YOUNG, MATURE, AND OLD RATS - INFLUENCE OF DIETARY RESTRICTION

Earlier studies have shown that hepatic vitamin A stores increase with age and that rats subjected to life-long dietary restriction (DR) hav e greater hepatic retinoid concentrations than ad libitum-fed rats, It was suggested that these changes may be attributed to altered intesti nal absorption, and so we measured retinol absorption in 3, 12, and 22 month-old female Sprague-Dawley rats fed ad libitum (AL) or a restric ted diet (40%) enriched (DR(+)) or not (DR) with vitamins and minerals , An in vivo model was used and lymph collected from the mesenteric du ct while rats were infused a micellar solution containing [H-3]retinol into the proximal duodenum, Aging significantly decreased lymph flow, and at all ages DR and DR(+) rats exhibited a higher flow than age-ma tched AL rats, Absorption of retinol was not significantly modified by age in AL and DR(+) rats, However, in the DR group, there was a marke d decrease in absorption between 3 and 12 months of age, Retinol absor ption was significantly higher in 12 and 22 month-old DR(+) rats than in age-matched AL rats, a finding that may be explained by both higher lymph flow rate and higher long-term vitamin A intake per body weight , In conclusion, the increased content of vitamin A in the livers of o lder AL rats is not associated with changes in intestinal absorption, In DR rats, however, retinoid accumulation in the liver may be explain ed by increased intestinal absorption of the vitamin, though other mec hanisms may be involved, A possible explanation may be a decreased out put of retinol from the liver as a result of lower metabolic needs, Th e lower serum vitamin A concentrations observed in DR rats would tend to support this hypothesis.