Kinetic characteristics of beta-carotene uptake and depletion in rat tissue.

Rats were fed a semi-purified diet supplemented with 0, 0.002, 0.02 and 0.2% beta-carotene (BC) for 21 weeks, followed by a 5-week depletion period. At various time points liver, adrenal, ovary, lung, heart, kidney, plasma, skin, brain and muscle were analyzed for BC content. The results indicated a dose-response effect between ingested BC and BC tissue content. The tissue saturation levels of BC, and time to reach saturation were determined in animals fed 0.2% BC diets. The half-life for BC was also determined. There was no apparent relationship among tissue content, rate of uptake and rate of depletion of BC. Each tissue studied was different. The absence of BC in fat suggests to us that BC distribution is not simply a matter of deposition into lipid depots. There was a wide range in tissue levels of BC; liver had the greatest value with 50 micrograms/g tissue, and muscle had the lowest value with 0.03 micrograms/g tissue. Plasma was saturated within 3 days, whereas liver, adrenal and ovary had not yet reached saturation at 147 days. The half-life varied from less than 3 days for plasma to 18 days for muscle.