Isoflavone content of rodent diets and its estrogenic effect on vaginal cornification in Pueraria mirifica-treated rats

Pueraria mirifica or White Kwao Krua has been extensively studied for its estrogenic effects on reproductive organs and bones using rodents as experimental animals. Commercial rodent diets are usually formulated with soybean products and therefore deliver a high dose of isoflavone phytoestrogens. Using high performance liquid chromatography, we determined the quantities of five major isoflavones (puerarin, daidzin, genistin, daidzein, and genistein) in five lots of standard rodent diets, a soybean-free diet, and two lots of R mirifica 'Wichai-III'. The concentrations of total isoflavones were 38.6-72.4 mg/100 g in the standard rodent diets, 6.1 mg/100 g in the soybean-free diet, and 123.2-157.3 mg/100 g in the P mirifica. While absent in the rodent diets, puerarin accounted for about half of the isoflavone content in P. mirifica. The levels of genistein and genistin in R mirifica were very low compared to the level found in the standard rodent diets. Given the same dose of 50 mg/kg BW/day of P. mirifica for 14 days, rats fed with standard rodent diet showed a significantly higher percentage of cornified cells than those fed with soybean-free diet. These findings suggest the potential presence of phytoestrogens in standard rodent diets and its liability to be a confounding factor in estrogenic or phytoestrogenic research.