Effect of Exogenous Gonadal Steroids on Reproductive Functions of the Indian Pygmy Field Mouse Mus terricolor

Different thresholds of gonadal steroids exert stimulatory or inhibitory effects on GnRH and gonadotropin release. During the reproductively active phase (RAP), the concentration of endogenous gonadal steroids remains high while, during reproductively inactive phase (RIP), it remains low. During RIP the HPG axis is sensitive to gonadal steroids but the circulatory levels of testosterone and estradiol remain low. During this phase one can observe conveniently the effects of gonadal steroids on the HPG axis in male or female rodents. Therefore, the aim of the present study was to find the effects of testosterone and estradiol on the reproductive functions of male and female Indian pygmy field mouse, Mus terricolor, during RIP. The male mice were injected aquaviron (commercially available testosterone, 1mg/100g body weight) while the female mice received estradiol-benzoate (25μg/100g body weight) for 15 consecutive days during the RIP. After completion of the treatment, a significant increase in the weights of gonads and accessory sex organs was noted in both the sexes. The biochemical constituents of accessory sex organs such as epididymal sialic acid, seminal vesicular fructose and uterine protein content reflected significant elevation accompanied by increased levels of plasma testosterone, estradiol and progesterone. Histologically, the gonads and accessory sex organs exhibited increased cellular activity. However, the gonadal cholesterol was significantly decreased in both the sexes. Over all, administration of gonadal steroids to both male and female mice accelerated the gonadal recrudescence but did not inhibit the reproductive functions when administered during the RIP. Therefore, it can be inferred from the present study that during the RIP the HPG axis is sensitive to gonadal steroids and, hence, exogenous gonadal steroids induce gonadal activity.