Exposure of Xenopus laevis tadpoles to finasteride, an inhibitor of 5-a reductase activity, impairs spermatogenesis and alters hypophyseal feedback mechanisms R Urbatzka 1 , B Watermann 2 , I Lutz 1 and W Kloas 1,3 1 Department of Inland Fisheries, IGB, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Mueggelseedamm 301, 12587 Berlin, Germany 2 Limnomar, Bei der Neuen Muenze 11, 22145 Hamburg, Germany 3 Department of Endocrinology, Institute of Biology, Humboldt-University, Invalidenstrasse 43, 10115 Berlin, Germany (Correspondence should be addressed to R Urbatzka who is now at Centre of Marine and Environmental Research, Rua dos Bragas 289, 4050-123 Porto, Portugal; Email: rurbatzka@ciimar.up.pt) Abstract Sexual steroids have major regulatory functions in gonadal development, maturation of gametes and sexual differentiation in vertebrates. Previous studies in amphibians provided evidence that dihydrotestosterone and activity of 5-a reductases might play a significant role in androgen-mediated reproductive biology. To test the involvement of 5-a reductases in maturation of gametes in amphibians, Xenopus laevis was exposed to finasteride (FIN), a known inhibitor of 5-a reductase enzyme activity. In a long-term exposure from stage 46 to 66, severe disruption of spermatogenesis was observed in histological analysis of testes as detected by occurrence of empty spermatocysts, while ovaries remained unaffected. Real-time PCR analyses of male and female brain revealed an increase of LHb mRNA and a decrease of FSHb mRNA in males, suggesting a signalling on testes that could result in increased steroidogenesis and reduced Sertoli cell proliferation. Accordingly, the mRNA expression of P450 side chain cleavage enzyme and 5-a reductase type 2 was increased in testes, while no effects could be observed on steroidogenic genes in ovaries. A short-term exposure to testosterone, FIN and testosteroneCFIN showed that transient effects of FIN targeted males selectively and, in particular, interfered with the hypothalamus–pituitary–gonad axis. Furthermore, a negative feedback of testosterone on LHb was observed on males and females. This study provides evidence that exposure of X. laevis to FIN, an inhibitor of 5-a reductases, impaired spermatogenesis and involved sex-specific hypophyseal feedback mechanisms. Journal of Molecular Endocrinology (2009) 43, 209–219 Introduction Synthesis of sexual steroids is a conserved process in vertebrates starting with cholesterol that is converted by the actions of multiple enzymes into testosterone. Testosterone can either exert androgen action by itself or can be further converted into dihydrotestosterone (DHT) or into 17b-oestradiol (Payne & Hales 2004). Leydig cells in testis and theca/granulosa cells in ovaries are the main producing cells of sexual steroids that are subsequently released into the bloodstream. Biological action in peripheral tissues often needs the conversion of testosterone into DHT that is accom- plished by the enzyme 5-a reductase. Two isozymes exist for 5-a reductase, named type 1 (Srd5a1) and type 2 (Srd5a2), which are differentially distributed in many tissues. In rats, Srd5a2 is confined to androgen- dependent tissues, while Srd5a1 is present in various tissues (Torres et al. 2003). Especially, Srd5a2 activity is believed to play a key role in androgen-regulated reproductive biology. In mammals, as in amphibians, the more potent androgen is DHT unlike in fish, where 11-ketotestos- terone is the most potent androgen (Norris 1997). DHT promotes in humans and mammals the development of external genitalia or androgenic tissues like prostate, while testosterone is responsible for the development of male internal genitalia. Finasteride (FIN), a well-known inhibitor of 5-a reductase activity with higher potency to Srd5a2 than to Srd5a1 (George et al. 1989, Prahalada et al. 1997, Ellsworth et al. 1998), was frequently used to experimentally unravel functions of 5-a reductases being involved in male pattern hair loss (Kawashima et al. 2004) or benign prostate hyperplasia or prostate cancer (Luo et al. 2003). If administered in utero, external genitalia were feminized in rats (Imperato- McGinley et al. 1992) or developed abnormalities in rhesus monkeys (Prahalada et al. 1997). Humans with deficiency of Srd5a2 developed feminized genitalia (Imperato-McGinley et al. 1981), and polymorphisms in Srd5a2 gene were associated with differences in sperm concentration and motility (Elzanaty et al. 2006). 209 Journal of Molecular Endocrinology (2009) 43, 209–219 DOI: 10.1677/JME-09-0058 0952–5041/09/043–209 q 2009 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology-journals.org