Estrogen-induced maternal behavior in hysterectomized-overiectomized virgin rats.

A single injection of 100 μg/kg estradiol benzoate (EB) either alone or in combination with 0.5 mg progesterone resulted in a significant reduction in the latency for the onset of maternal behavior in hysterectomized-ovariectomized virgin rats as compared to the latencies of groups which either remained intact or were hysterectomized, hysterectomized-ovariectomized, hysterectomized-ovariectomized and treated with 20 μg/kg EB, or ovariectomized-sham hysterectomized and injected with 100 μg/kg EB. In contrast to recent research, there was no shortening of the maternal latencies when ovariectomy or combined hysterectomy-ovariectomy was performed 8 weeks prior to testing while the administration of EB 8 weeks postoperatively was still effective in stimulating short-latency maternal care in hysterectomized-ovariectomized females and increased the percentage of ovariectomized sham hysterectomized animals responding maternally. It was concluded that estrogen is capable of inducing, not suppressing, maternal behavior in virgin rats and that the uterus may play an important but as yet undetermined role.