RESUMEN
Thyroid hormones, acting via their cognate thyroid receptors (TRs) act as mediators and modulators of several physiological processes and homeostasis. A clear role for the TRs in reproduction has not yet been established although several lines of recent evidence suggest that they are involved in the regulation of reproduction. To further study the role of TRs in control of reproduction, we investigated homologous regulation of TR subtypes in the gonads of goldfish, in vivo and in vitro. It was found that tri-iodothyronine (T(3)) down-regulates the traditional TRs (TRα-1 and TRß) and up-regulates a dominant-negative form, TRα-t. This indicates a 'feedback' mechanism whereby an acute treatment with T(3) down regulates further T(3) mediated response. The results provide novel information on auto-regulation of TRs in the goldfish ovary and testis, and support the hypothesis that thyroid hormones are involved in the control of reproduction.
Asunto(s)
Retroalimentación Fisiológica/fisiología , Carpa Dorada/genética , Ovario/metabolismo , Receptores de Hormona Tiroidea/genética , Testículo/metabolismo , Animales , Células Cultivadas , Retroalimentación Fisiológica/efectos de los fármacos , Femenino , Regulación de la Expresión Génica/efectos de los fármacos , Carpa Dorada/metabolismo , Carpa Dorada/fisiología , Homeostasis/efectos de los fármacos , Homeostasis/genética , Homeostasis/fisiología , Masculino , Ovario/efectos de los fármacos , Receptores de Hormona Tiroidea/metabolismo , Receptores de Hormona Tiroidea/fisiología , Testículo/efectos de los fármacos , Triyodotironina/farmacologíaRESUMEN
There is increasing evidence that thyroid hormones influence reproduction in vertebrates. However, little information is available on the mechanisms by which this happens. As a first step in determining these mechanisms, we test the hypothesis that the estrogen receptor subtypes (ERalpha, ERbeta-1, and ERbeta-2) are regulated by the thyroid hormone, (T(3)), in the gonads of goldfish. All three subtypes were down-regulated by T(3) in the testis or ovary. We also found evidence that T(3) decreased pituitary gonadotropin expression and decreased transcript for gonadal aromatase. Collectively, it appears that T(3) acts to diminish estrogen signaling by (1) decreasing pituitary LH expression and thus steroidogenesis, (2) down-regulating gonadal aromatase expression and thus decreasing estrogen synthesis from androgens, and (3) decreasing sensitivity to estrogen by down-regulating the ER subtypes. Goldfish are seasonal breeders, spawning once a year, and thus have two distinct periods of growth: somatic and reproductive. Circulating thyroid hormone levels have been found to increase just after spawning. Therefore, we propose that this may be an endocrine mechanism that goldfish use to switch their energy expenditure from reproductive to growth efforts in the goldfish.