Effects of genistein exposure on sexually dimorphic behaviors in rats.

The phytoestrogen genistein, the principal isoflavone in soybeans, has adverse effects on animal reproduction. As adult physiology and behavior are sensitive to perturbation by developmental estrogens, exposure to genistein during development may produce behavioral alterations as well. Pregnant rats were fed soy-free diets containing 0, 25, 250, or 1250 ppm genistein (approximately 0, 2, 20, or 100 mg/kg/day) beginning on gestational day 7, and offspring continued on these diets through postnatal day (PND) 77. Male and female offspring were assessed for levels of sexually dimorphic behaviors: open field activity, play behavior, running wheel activity, and consumption of saccharin- and sodium chloride-flavored solutions. Consumption of the salt solution was affected by genistein, with animals in the 1250-ppm group drinking significantly more than controls; consumption of plain water was unaffected. Genistein treatment also significantly affected play behavior; although no treated group was significantly different from controls, and the effect was not sexually dimorphic. Running wheel activity and saccharin solution consumption showed significant sex differences, but no effects of genistein treatment. Gestational duration, total and live pups per litter, and total and live litter sex ratios were not significantly affected by genistein. However, average weight per live pup at birth and offspring body weights from PND 42-77 were significantly decreased in the 1250-ppm group. Body weight and food intake for the dams were also significantly decreased in the 1250-ppm group. These results indicate that developmental genistein treatment, at levels that decrease maternal and offspring body weight, causes subtle alterations in some sexually dimorphic behaviors.