Effects of genistein exposure on sexually dimorphic behaviors in rats

The phytoestrogen genistein, the principal isoflavone in soybeans, has adve rse effects on animal reproduction. As adult physiology and behavior are se nsitive to perturbation by developmental estrogens, exposure to genistein d uring development may produce behavioral alterations as well. Pregnant rats were fed soy-free diets containing 0, 25, 250, or 1250 ppm genistein (appr oximately 0, 2, 20, or 100 mg/kg/day) beginning on gestational day 7, and o ffspring 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 s alt solution was affected by genistein, with animals in the 1250-ppm group drinking significantly more than controls; consumption of plain water was u naffected. Genistein treatment also significantly affected play behavior; a lthough no treated group was significantly different from controls, and the effect was not sexually dimorphic. Running wheel activity and saccharin so lution consumption showed significant sex differences, but no effects of ge nistein treatment. Gestational duration, total and live pups per litter, an d total and live litter sex ratios were not significantly affected by genis tein. However, average weight per live pup at birth and offspring body weig hts from PND 42-77 were significantly decreased in the 1250-ppm group. Body weight and food intake for the darns were also significantly decreased in the 1250-ppm group. These results indicate that developmental genistein tre atment, at levels that decrease maternal and offspring body weight, causes subtle alterations in some sexually dimorphic behaviors.