To further investigate the effect of dietary vitamin A (VA) intake on milk VA concentrations and pup VA status, female rats were fed 2 concentrations of VA [0 (n = 9) or 50 micromol/kg diet (n = 10)] during pregnancy and lactation. Plasma retinol concentrations were significantly higher (30-40%) during lactation than before pregnancy or after weaning but were not influenced by dietary VA. In rats fed VA, VA concentrations during lactation were significantly higher in milk (1.5-3 times), mammary tissue (>100%), liver (4 times), pup plasma (20-40%), and pup liver (1.1-6.7 times). In Expt. 2, when VA intake was switched on d 7 of lactation from 0 to 50 micromol/kg, milk VA concentrations (2.24 +/- 0.42 micromol/L; mean +/- SD, n = 6) increased significantly (1.7 times) by d 9 to the same level as in rats administered 50 micromol/kg (6.04 +/- 0.60 micromol/L; n = 6). When VA was removed from the diet on d 7, concentrations declined significantly (by 50%) and by d 11 were the same as those in rats given 0 micromol/kg. We conclude that the rapid effect of changes in dietary VA intake are attributable to changes in the delivery of chylomicron VA to mammary tissue and milk.