621
DIFFERENTIAL EFFECTS OF DIETARY SOY AND ISOFLAVONES ON THE REPRODUCTIVE TRACT OF THE INTACT FEMALE RAT.
Cooke, Leslie1, Pyter, Leah1, Nakai, Masaaki1, Jeffery, Elizabeth2, Bahr, Janice1, 1 2
ABSTRACT- Soy is a rich source of protein, which contains phytoestrogens called isoflavones. Isoflavones display estrogenic activity through their binding to the estrogen receptor. Studies on the estrogenic effects of soy on female physiology have shown there are more beneficial effects than negative effects. Soy and isoflavones are being promoted to have healthful effects on bone, blood cholesterol concentrations and the heart. However, little consideration is given to the possible negative effects phytoestrogens could have on the reproductive tract, a known target for estrogen. Therefore, our goal was to determine if a diet rich in soy or isoflavones would induce histological changes in the reproductive tract of intact female rats. Three month old intact female Sprague-Dawley rats were divided into 7 groups (n=10-12 each) and fed one of the following diets: 1) control (200g casein/kg diet); 2) low soy (100g soy protein, 100g casein; LS); 3) high soy (200g soy protein; HS); 4) low isoflavone extract (200g casein + isoflavone content of group 2; LE); 5) high isoflavone extract (200g casein + isoflavone content of group 3; HE); 6) low soy without isoflavones (100g isoflavone-free soy protein, 100g casein; LW) and 7) high soy without isoflavones (200g isoflavone-free soy protein; HW). Rats were fed daily for 3 months and remaining food was weighed and recorded. After 3 months, the reproductive tract was removed, uterine weight was recorded, and the tissue was prepared for histology. Uterine wet weights of the treatment groups did not differ from controls. Histologically, no marked alterations were noted in the cervix and vagina in any group. However, a change from simple columnar epithelium to stratified squamous epithelium was observed in the uterine glands of 1 animal in the HS group (10%) and 5 animals in the HE group (42%), indicating that endometrial squamous metaplasia was induced in these animals. These results suggest that diets rich in soy isoflavones can cause pathological changes in the uterus, indicative of estrogenic stimulation. In contrast the cervix and vagina did not display any abnormal histology. On the contrary, consumption of a soy diet containing the same amounts of isoflavones as LE and HE diets caused little or no histological changes in the uterus. (NIH-AG17521 and IL Council on Food and Agricultural Research).
KEY WORDS: isoflavones, soy, rat, uterus