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Differential Alteration of the Reproductive Axis by Testosterone and Estrogen in Peripubertal and Adult Male Siberian Hamsters (Phodopus sungorus)¹

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

In male Siberian hamsters, administration of adult physiological levels of testosterone (T) and estrogen (E₂) to juveniles inhibited pubertal onset by distinct pathways. It is presently unclear if T and E₂ also exert an inhibitory effect on the reproductive function of sexually mature and sexually maturing hamsters. This study aims to determine if there is an age-dependent decline in the sensitivity of the hypothalamic-pituitary-gonadal (HPG) axis to these inhibitory steroids and if their actions remain distinct. Peripubertal and adult male Siberian hamsters were implanted with a silastic capsule containing T, E₂, or cholesterol (Ch, control). Testosterone treatment significantly reduced testes mass and length and impaired spermatogenesis in both ages. In contrast, E₂ treatment reduced testes mass only in peripubertal, but not adult, animals. In fact, E₂ treatment significantly increased testes mass in adults without altering spermatogenesis. In addition, circulating E₂ is very high immediately prior to pubertal onset and declines thereafter. Our results showed the inhibitory effects of T persist into adulthood whereas those of E₂ subside as the animals become sexually mature. The decreased sensitivity of the HPG axis to the inhibitory effects of E₂ in adult animals and the high level of circulating E₂ immediately prior to pubertal onset suggest E₂ may play an important role in the regulation of puberty in this species.

First decision: 11 February 2002.

¹ This work was supported in part by NSF IBN-9996398 to P.-S.T. and a Research Grant from the University of Colorado to G.R.L.

² Correspondence: Toni R. Pak, Department of Environmental, Population, and Organismic Biology, University of Colorado, Campus Box 334, Boulder, CO 80309. FAX: 303 492 8699; toni.pak{at}colorado.edu

This article has been cited by other articles:

				T. R. Pak, G. R. Lynch, D. M. Ziegler, J. B. Lunden, and P.-S. Tsai Disruption of pubertal onset by exogenous testosterone and estrogen in two species of rodents Am J Physiol Endocrinol Metab, January 1, 2003; 284(1): E206 - E212. [Abstract] [Full Text] [PDF]