Effect Of The Female Hormone In Cow's Milk On The Steroid Metabolism And Pubertal Development In Young Female Rats

Objective: The estrogen from food, especially modern cow's milk, which contains considerable amounts of estrogens, has been concerned by more and more people. The hypothesis presumes that milk is responsible, at least in part, for the increased incidence of reproductive abnormalities. The results of epidemiologic studies of this hypothesis are inconclusive. To assess the effects of modern milk on the young female steroid metabolism and development of reproductive system, we conducted an animal study in our laboratory.Methods: Twenty-one-day old female SD rats were randomly divided into Milk group (n=12) and Control group (n=12). Each rat in the Milk group had been fed on 20 ml whole milk every day. Meanwhile, each one in the Control group had been fed on assorted feeds, which contained the same amount of gluten, fat, lysine and calcium as the milk given to the Milk group. The 24h-urine estriol and progesterone were detected by the Immunochemiluminometric assays (ICMA) after the rats were fed 10 days. In addition, for each rat, the times of vaginal opening were recorded, and the vaginal smears were performed every day. Finally, when the rats was fifty-five-day's old, they were killed. Before killing, the final body weight and length were measured under anaesthesia . And the uterine and ovarial weight were measured and compared.Results: The amounts of urinary FE3 (pg/24h), urinary TE3 (pg/24h) and urinary Pro (ng/24h) in the Milk group were higher than that in the Control group [(5078.1±1102.8) vs. (3032.7±1180.9), P<0.01; [(6074.4±1465.6) vs. (3446.7±1149.0), P<0.01; (434.36±167.61) vs. (221.30±159.15), P<0.01], respectively; The urinary TE3/Cr concentration ratio in the Milk group was higher than that in the Control group [(213.9±43.4) vs. (171.9±26.4), P<0.01]; The amount of the vaginal smear in alpha phase in Milk group was lower than that in the Control group (P<0.05); The final weights in Milk group were lower than that in the Control group (P<0.05). The means of the uterine and ovarial weights in the Milk group were higher than that in the Control group, though they were not significant different.Conclusion: The cow's milk in this test, which contains considerable amounts of estrogens, might affect the steroid metabolism and the hypothalamus-hypophysis-gonad axis, and delay the pubertal development in young female rats.