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Testosterone and Estrogen Act via Different Pathways to Inhibit Puberty in the Male Siberian Hamster (Phodopus sungorus)

Department of Environmental, Population and Organismic Biology, University of Colorado, Boulder, Colorado 80309

Address all correspondence and requests for reprints to: Toni R. Pak, Department of Environmental, Population and Organismic Biology, University of Colorado, Campus Box 334, Boulder Colorado 80309. E-mail: toni.pak{at}colorado.edu

The peripubertal transition in male mammals is accompanied by a gradual decrease in sensitivity to the inhibitory effects exerted by gonadal hormones, such as T and E2. Here, we investigated the effects of chronic T and its metabolites, 5-dihydrotestosterone and E2 on the hypothalamo-pituitary-gonadal axis at puberty. We also examined if T effects are distinct or mediated through its conversion to 5-dihydrotestosterone or E2. Twenty-day-old male Siberian hamsters were sc implanted with a SILASTIC brand capsule containing varying doses of T, 5-dihydrotestosterone, or E2. Several functional parameters of the hypothalamo-pituitary-gonadal axis were evaluated including hypothalamic GnRH concentration, pituitary and plasma FSH levels, pituitary FSH and LH mRNA, and testicular status. Our results showed that gonadal steroids inhibited puberty in a dose-dependent manner as evaluated by testes mass (undiluted steroid: T, 27 ± 3 mg; 5-dihydrotestosterone, 18 ± 1 mg; and E2, 62 ± 4 mg relative to cholesterol-implanted controls, 510 ± 42 mg). Also, T decreased plasma FSH below detectable levels, but pituitary FSH concentration was unaffected (1.37 ± 0.16 ng/µg protein) while E2-treated hamsters had normal plasma FSH levels (3.5 ± 0.98 ng/ml) yet significantly lower pituitary FSH concentration (0.09 ± 0.04 ng/µg protein). These results showed that the pathways of T and E2 action on the hypothalamo-pituitary-gonadal axis are distinct.

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