VITAMIN-A PLASMA KINETICS IN NORTHERN FUR SEALS (CALLORHINUS-URSINUS), USING VITAMIN-A(2) AS A TRACER

Vitamin A(2) (3,4-didehydroretinol), a natural analog of retinol, was used to determine the plasma kinetics of vitamin A in two northern fur seals (Callorhinus ursinus) receiving two levels of vitamin A supplem ents. After a single oral dose, the time required to reach maximum pla sma vitamin A(2) concentration for both subjects was approximately 2 h , which is much less than the 8-12 h observed with humans. The level o f vitamin A supplementation did not affect base-line plasma retinol co ncentrations or plasma kinetics. The mean sojourn time, the average ti me spent by a molecule of vitamin A in the body before being lost, was 40 days for one animal and 73 days for the other. The daily vitamin A requirement estimated from the disposal rate was 0.32-0.64 mu mol per day for the two animals. The presumed upper safe level was calculated at 1.3-6.4 mu mol vitamin A per day. It would appear that the fish di et commonly provided to these animals can meet their vitamin A require ments. Supplementation may only be warranted to offset vitamin loss du ring storage and handling of the food. However, a conservative approac h to supplementation should be used, as chronic vitamin A toxicity is a danger.