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 chylomicrons vs, hole retinol-binding protein to milk vitamin A, female rats were 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 incorporated into each diet beginning on d 6 of lactation. Vitamin A concentrations 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 level of vitamin A. In both groups, vitamin A specific activities in plasma and 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 plasma at all times in both groups. The estimated minimum contribution of chylomicrons to milk vitamin A was 32 +/- 3% in rats fed the lower level of vitamin A vs. 52 +/- 10% at the higher level (P = 0.014). We concluded that dietary 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 contrast to milk, mammary tissue vitamin A turns over very slowly.