VITAMIN A TRANSPORT IN THE RAT

Abstract

Rats deficient in vitamin A and maintained on diets containing 0, 4, or 20% protein (casein) were repleted orally with 0, 10, 40, 80, or 160 μg vitamin A alcohol per day for 7 days. Plasma vitamin A rose with increasing amounts of administered vitamin A until a plateau was reached (at the dose level of 10 μg in the 0% protein group, and the dose level of 40 μg in the other groups), suggesting that plasma saturation with vitamin A had occurred. This was supported by an increase in the deposition of the vitamin in the liver at the dose level of 40 μg vitamin A. The actual level of plasma vitamin A attained at plasma saturation varied directly with the amount of dietary protein fed and, consequently, with plasma protein concentration, but was limited by food restriction in a control group fed a diet containing 20% protein to a level well below that obtained by a control group fed ad libitum with the same diet.Plasma vitamin A was shown to be statistically related to plasma albumin at all levels of administration of the vitamin, and to α₁-globulin after plasma saturation with vitamin A had occurred.The data indicate the existence of a plasma protein carrier for vitamin A. The participation of an albumin subfraction in the transport mechanism is discussed.