Liver Storage of Vitamin A by Male and Female Rats

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Abstract
Vitamin A-free rats were given carotene in oil or vegetables, or halibut liver oil, then killed. Vitamin A was assayed by the SbCl3 test in the livers or kidneys or both. The standard deviation of a liver determination of vitamin A within any one group varied with the 0.74th power of the mean liver value for the group. After they had ingested carotene, more vitamin A was found in the livers of females than of males. Both lost their stores at similar rates. Hence male livers depleted sooner than female and the female/male storage ratio increased with time. The absorption efficiency of carotene was not linked to sex. Neither sex showed correlation between storage and growth rate. Correlation was negligible between storage and body weight among rats of one sex at the same age similarly dosed. Infant rats had negligible sex differences in body weight and liver storage. Young rats stored more than middle-aged rats from the same intake, but old rats stored the same proportion as middle-aged rats of similar size. Twin females, though weighing more and growing faster than duodecet males, stored more vitamin A. On vitamin intakes too low for maximum growth, males outgrew females. After being given a vitamin A-free diet from weaning, or after one dose of vitamin A, males showed deficiency symptoms only slightly sooner than females. Males and females had similar kidney levels shortly after a dose. The level in male kidneys increased with time, but in female kidneys no comparable rise was found. Male and female dose-response curves had different slopes. The difference between male and female liver stores at different doses was a constant proportion (11%) of the dose. The threshold dose, below which there was no storage, was higher for males than for females. Items 5, 8, 9 and 11 show that the sex-liver-storage difference cannot be related to different growth rates. Another hypothesis, that liver storage is inversely controlled by body weight, is supported by items 7 and 11, refuted by 6 and 8. This and other possibilities are discussed under Conclusions.