Thyroid hormone and reproduction: Regulation of estrogen receptors in goldfish gonads

Abstract

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.

Developmental Profiles and Thyroid Hormone Regulation of Brain Transcripts in Frogs: A Species Comparison with Emphasis on <i>Physalaemus</i> <i>pustulosus</i>

“…This negative regulation has been observed in mammals and fish, where T3 suppresses Cyp19 mRNA and activity in gonad (testes and ovaries) in vivo and in vitro cultures: goldfish [Nelson et al, 2010], mice [Cecconi et al, 1999;Catalano et al, 2003], pigs [Gregoraszczuk et al, 1998], and rats [Ulisse et al, 1994;Ando et al, 2001;Hatsuta et al, 2004]. In contrast, in S. tropicalis, T3 did not affect brain cyp19 but instead increased srd5alpha1 and srd5alpha2 mRNA ( table 3 ).…”

Crossover of the Hypothalamic Pituitary–Adrenal/Interrenal, –Thyroid, and –Gonadal Axes in Testicular Development

“…(3) Exposure to cortisol results in an increase of the androgen-related machinery and subsequent masculinization in fish (25–27, 84), and mammals (32). (4) Exposition of thyroid hormones could inhibit the aromatase (P450arom/ cyp19a1 ) activity or expression in fish (36, 85), amphibians (46, 47), and mammals (58, 59, 75). TRH, thyrotropin-releasing hormone; Dio1, deiodinase type 1; Dio2, deiodinase type 2; T4, thyroxine; ACTH, pituitary adrenocorticotropic hormone; T (testosterone) 11β-HSD2, type 2 isozyme of 11β-hydroxysteroid dehydrogenase; 11-KT, 11-ketotestosterone; 5α-DHT, 5α-dihydrotestosterone.…”

Rapid method for the measurement of circulating thyroid hormones in low volumes of teleost fish plasma by LC-ESI/MS/MS

“…Thyroid hormones play a crucial role in brain development and small changes in maternal or fetal/early life stage thyroid hormone levels can elicit severe motor skill deficiencies and cognitive impairments [6]. In fishes, thyroid hormones are key mediators of many physiological, developmental, and behavioral processes, including growth and metamorphic transitioning [7, 8], osmoregulation [9], olfactory imprinting [10], interrenal regulation [11], otolith formation [12], and reproduction [13, 14], often acting in concert with other hormones. For instance, smoltification among salmonids (parr–smolt transformation to allow for seawater tolerance) is regulated by interactions between thyroid hormones, cortisol, insulin, and prolactin [15, 16].…”