TESTOSTERONE REGULATION OF GONADOTROPIN PRODUCTION IN GOLDFISH

Gonadotropin (GTH) production in teleosts is primarily regulated by co mplex interrelationships between the sex steroids, neurotransmitters, and GTH-releasing hormone (GnRH). Both steroids and GnRH individually regulate GTH secretion and subunit (alpha and beta) gene expression. S teroids may exert their actions directly at the level of pituitary, or indirectly by affecting brain GnRH and other neurotransmitters, causi ng stimulation or inhibition of GTH production. This paper reviews stu dies concerning the effects of testosterone on basal and GnRH-induced GTH production in the goldfish pituitary. Overall, the findings demons trate that testosterone and GnRH individually exert stimulatory action s on GTH production, whereas a combination of testosterone and GnRH tr eatments reduce GTH subunit mRNA levels in the goldfish pituitary. The secretion of GTH hormones, however, is stimulated by GnRH, as well as by combined testosterone and GnRH treatments. The contributing factor s that could explain the observed inhibitory effects include decreased transcription, increased posttranscriptional degradation, or increase d translation of GtH subunit mRNA in the goldfish pituitary. At the pr esent time, however, we are not able to distinguish between these poss ibilities. (C) 1998 Elsevier Science Inc. All rights reserved.