Increased rat mammary tissue vitamin A associated with increased vitamin A intake during lactation is maintained after lactation

Although increases in dietary vitamin A increase milk vitamin A, little is known about effects of vitamin A intake on mammary tissue vitamin A levels during and after the reproductive cycle. First, we measured vitamin A concentrations in milk, mammary tissue and liver of lactating rats fed 0, 4, or 50 μmol of vitamin A/kg diet during pregnancy and through d 12 of lactation. Liver vitamin A concentration was significantly affected by diet in lactating females and pups 12 d after parturition. Milk vitamin A concentrations were significantly higher (7.1 ± 2.2 μmol/L, n = 8) in dams fed 50 μmol/kg than in those fed 0 or 4 μmol/kg (1.9 ± 0.3, n = 5 and 2.9 ± 0.7 μmol/L, n = 7; P < 0.001), as were mammary tissue vitamin A concentrations (5.1 ± 1.1 versus 2.2 ± 0.4 and 2.4 ± 0.6 nmol/g; P < 0.001). Next, we maintained female rats on 50 or 10 μmol vitamin A/kg diet during pregnancy and lactation and then on 4 μmol/kg diet after pups were weaned on d 21. On d 21, mammary tissue vitamin A concentrations were 3.14 ± 0.75 versus 1.52 ± 0.21 nmol/g in dams fed 50 versus 10 μmol/kg (n = 4/group; P < 0.001). Mammary tissue vitamin A concentrations were not significantly affected by time from 7 to 49 d after lactation and averaged 8.5 ± 0.4 and 4.9 ± 0.8 nmol/g on d 49 in dams fed 50 versus 10 μmol/kg (n = 4; P < 0.001). We conclude that diet-induced differences in rat mammary tissue vitamin A developed during pregnancy and lactation are maintained for ≥7 wk after lactation.