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      Estradiol and reproduction in the South American toad Rhinella arenarum (Amphibian, Anura).

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          Abstract

          Rhinella arenarum is a South American toad with wide geographic distribution. Testes of this toad produce high amount of androgens during the non reproductive season and shift steroid synthesis from androgens to 5α-pregnanedione during the breeding. In addition, plasma estradiol (E2) in males of this species shows seasonal variations but, since testes of R. arenarum do not express aromatase, the source of plasma E2 remained unknown for several years. However, the Bidder's organ (BO), a structure located at one pole of each testis, is proposed to be the main source of E2 in male's toads since it expresses several steroidogenic enzymes and is able to produce E2 from endogenous substrates throughout the year. In addition, there were significant correlations between plasma E2 and total activity of BO aromatase, and between plasma E2 and the amount of hormone produced by the BO in vitro. In the toad, apoptosis induced by in vitro treatment with E2 was mostly detected in spermatocytes during the breeding and in spermatids during the post-reproductive season, suggesting that this steroid has an important role in controlling spermatogenesis. However, in vitro treatment with E2 had no effect on proliferation. This evidence suggests that the mechanism of action of E2 on amphibian spermatogenesis is complex and more studies are necessary to fully understand the role of estrogens regulating the balance between cellular proliferation and apoptosis. In addition, in R. arenarum in vitro studies suggested that E2 has no effect on CypP450c17 protein levels or enzymatic activity, while it reduces 3β-hydroxysteroid dehydrogenase/isomerase (3β-HSD/I) activity during the post reproductive season. As well, E2 regulates FSHβ mRNA expression all over the year suggesting a down regulation process carried out by this steroid. The effect on LHβ mRNA is dual, since during the reproductive season estradiol increases the expression of LHβ mRNA while in the non-reproductive season it has no effect. In conclusion, the effect of E2 on gonadotropins and testicular function is complex, not clearly understood and probably varies depending on the species. The aim of the current article is to review evidence on reproductive endocrinology and on the role of estradiol regulating reproduction in amphibians, with emphasis on the South American species Rhinella arenarum.

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          Author and article information

          Journal
          Gen Comp Endocrinol
          General and comparative endocrinology
          Elsevier BV
          1095-6840
          0016-6480
          March 01 2019
          : 273
          Affiliations
          [1 ] Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Biodiversidad y Biología Experimental, Buenos Aires, Argentina; Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA - CONICET), Buenos Aires, Argentina. Electronic address: mflorenciascaia@bg.fcen.uba.ar.
          [2 ] Instituto de Diversidad y Evolución Austral (IDEAus - CONICET), Puerto Madryn, Chubut, Argentina.
          [3 ] Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Biodiversidad y Biología Experimental, Buenos Aires, Argentina. Electronic address: czuchlej@bg.fcen.uba.ar.
          [4 ] Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Biodiversidad y Biología Experimental, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina. Electronic address: nceballo@bg.fcen.uba.ar.
          Article
          S0016-6480(17)30847-X
          10.1016/j.ygcen.2018.03.018
          29555118

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