Testosterone and estrogen act via different pathways to inhibit puberty in the male Siberian hamster (Phodopus sungorus).
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, 5alpha-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 5alpha-dihydrotestosterone or E2. Twenty-day-old male Siberian hamsters were sc implanted with a SILASTIC brand capsule containing varying doses of T, 5alpha-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; 5alpha-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/microg 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/microg protein). These results showed that the pathways of T and E2 action on the hypothalamo-pituitary-gonadal axis are distinct.
Pak
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TR
Department of Environmental, Population and Organismic Biology, University of Colorado, Boulder, Colorado 80309, USA. toni.pak@colorado.edu
Lynch
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GR
Tsai
P S
PS
D000818:Animals; D006224:Cricetinae; D013196:Dihydrotestosterone / Q000494:pharmacology; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000235:genetics; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D007031:Hypothalamus / Q000378:metabolism; D007986:Luteinizing Hormone / Q000235:genetics; D008297:Male; D009929:Organ Size / Q000187:drug effects; D017111:Phodopus; D010902:Pituitary Gland / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013737:Testis / Q000033:anatomy & histology; D013739:Testosterone / Q000097:blood / Q000494:pharmacology*; D013997:Time Factors
D012333:RNA, Messenger; D013196:Dihydrotestosterone; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone