Vitamin A intake affects the contribution of chylomicrons vs. retinol-binding protein to milk vitamin A in lactating rats

To investigate the influence of vitamin A intake on the contribution of chy lomicrons vs, hole retinol-binding protein to milk vitamin A, female rats w ere fed diets containing either 10 (n = 6) or 50 mu mol vitamin A/kg body ( n = 4) during pregnancy and through d 13 of lactation. [H-3]Vitamin A was i ncorporated into each diet beginning on d 6 of lactation. Vitamin A concent rations on d 13 were significantly higher in dam liver(x 3), pup liver(x 2. 6), milk(x 2.5) and mammary tissue (x 1.3) in rats consuming the higher lev el of vitamin A. In both groups, vitamin A specific activities in plasma an d milk reached apparent plateaus by 2.33 d after addition of [H-3]vitamin A to the diets. Vitamin A specific activity in milk was higher than in plasm a at all times in both groups. The estimated minimum contribution of chylom icrons to milk vitamin A was 32 +/- 3% in rats fed the lower level of vitam in A vs. 52 +/- 10% at the higher level (P = 0.014). We concluded that diet ary vitamin A, like triglycerides, may be directed to mammary tissue during lactation for preferential secretion into milk; thus, increasing vitamin A intakes will increase the contribution of dietary vitamin A to milk. In co ntrast to milk, mammary tissue vitamin A turns over very slowly.