Biology of Reproduction, Vol 44, 951-960, Copyright © 1991 by Society for the Study of Reproduction

ARTICLES

Testosterone and estradiol potentiate the serum gonadotropin response to gonadotropin-releasing hormone in goldfish

VL Trudeau, RE Peter and BD Sloley
Department of Zoology, University of Alberta, Edmonton, Canada.

The effects of gonadal steroids on gonadosomatic index (GSI; gonad wt/total body wt x 100), pituitary gonadotropin (GTH) content, and serum GTH response to [D-Ala6,Pro9-Net]-luteinizing hormone-releasing hormone (LHRH-A) were investigated throughout the seasonal reproductive cycle of the goldfish. Gonad-intact female fish were implanted i.p. for 5 days with silastic pellets containing no steroid (blank), testosterone (T; 100 micrograms/g), or estradiol (E2; 100 micrograms/g). The serum GTH response at 6 h following i.p. injection of saline or 0.1 microgram/g LHRH-A was assessed. In blank-implanted, saline-injected animals, seasonal variations in GSI, pituitary GTH content, and serum GTH levels were evident; maximal and minimal levels were noted in the spring and summer months, respectively. In blank- implanted fish, LHRH-A effectively stimulated GTH release in females undergoing gonadal recrudescence (late autumn and winter) and in sexually mature (spring) females, but not in sexually regressed (summer and early autumn) females. Implantation of T or E2 raised serum steroid levels to those found during ovulation in goldfish. Steroid treatments did not affect unstimulated serum GTH levels at any time of the year. Testosterone effectively potentiated the serum GTH response to LHRH-A during the entire reproductive cycle, whereas the positive effects of E2 were evident in sexually regressed and post-spawning females only. Both T and E2 potentiated the GTH response to LHRH-A in male fish. To examine the involvement of T aromatization in mediating its actions on induced GTH secretion, male and female fish were implanted with T or the nonaromatizable androgens 5 alpha-dihydroxytestosterone (DHT; 100 micrograms/g) and 11-keto-testosterone (11-KT; 250 micrograms/animal). Testosterone potentiated the GTH response to LHRH-A in both males and females whereas DHT and 11-KT were without effect. Furthermore, the positive action of T on induced GTH secretion was blocked by 2-day pretreatment with the aromatase inhibitor 1,4,6-androstatrien-3,17- dione (100 or 300 micrograms/g). Multiple i.p. injections of hCG (0.2 microgram/g every 3 days for 39 days), probably through stimulation of endogenous T secretion, resulted in potentiation of the GTH response to LHRH-A in mature male goldfish. These results clearly demonstrate that T, through aromatization to E2, can increase pituitary responsiveness to exogenous LHRH-A in gonad-intact male and female goldfish.

This article has been cited by other articles:

				F.-P. Yen, Y.-H. Lee, C.-L. He, J.-D. Huang, L.-T. Sun, S. Dufour, and C.-F. Chang Estradiol-17{beta} Triggers Luteinizing Hormone Release in the Protandrous Black Porgy (Acanthopagrus schlegeli Bleeker) Through Multiple Interactions with Gonadotropin-Releasing Hormone Control Biol Reprod, January 1, 2002; 66(1): 251 - 257. [Abstract] [Full Text]

				J.E.B. Cavaco, J. van Baal, W. van Dijk, G.A.M. Hassing, H.J. Th. Goos, and R.W. Schulz Steroid Hormones Stimulate Gonadotrophs in Juvenile Male African Catfish (Clarias gariepinus) Biol Reprod, May 1, 2001; 64(5): 1358 - 1365. [Abstract] [Full Text]

				F.E.M. Rebers, G.A.M. Hassing, M.A. Zandbergen, H.J.Th. Goos, and R.W. Schulz Regulation of Steady-State Luteinizing Hormone Messenger Ribonucleic Acid Levels, De Novo Synthesis, and Release by Sex Steroids in Primary Pituitary Cell Cultures of Male African Catfish, Clarias gariepinus Biol Reprod, April 1, 2000; 62(4): 864 - 872. [Abstract] [Full Text]

				V. Trudeau, O Kah, J. Chang, B. Sloley, P Dubourg, E. Fraser, and R. Peter The inhibitory effects of (gamma)-aminobutyric acid (GABA) on growth hormone secretion in the goldfish are modulated by sex steroids J. Exp. Biol., January 5, 2000; 203(9): 1477 - 1485. [Abstract] [PDF]

				T. S. Sperry and P. Thomas Identification of Two Nuclear Androgen Receptors in Kelp Bass (Paralabrax clathratus) and Their Binding Affinities for Xenobiotics: Comparison with Atlantic Croaker (Micropogonias undulatus) Androgen Receptors Biol Reprod, October 1, 1999; 61(4): 1152 - 1161. [Abstract] [Full Text]

				I. A. Khan, M. B. Hawkins, and P. Thomas Gonadal Stage-Dependent Effects of Gonadal Steroids on Gonadotropin II Secretion in the Atlantic Croaker (Micropogonias undulatus) Biol Reprod, September 1, 1999; 61(3): 834 - 841. [Abstract] [Full Text]

				T. S. Sperry and P. Thomas Characterization of Two Nuclear Androgen Receptors in Atlantic Croaker: Comparison of Their Biochemical Properties and Binding Specificities Endocrinology, April 1, 1999; 140(4): 1602 - 1611. [Abstract] [Full Text]

				J. E. B. Cavaco, C. Vilrokx, V. L. Trudeau, R. W. Schulz, and H. J. T. Goos Sex steroids and the initiation of puberty in male African catfish (Clarias gariepinus) Am J Physiol Regulatory Integrative Comp Physiol, December 1, 1998; 275(6): R1793 - R1802. [Abstract] [Full Text] [PDF]

				M. C. H. Holland, S. Hassin, and Y. Zohar Effects of Long-Term Testosterone, Gonadotropin-Releasing Hormone Agonist, and Pimozide Treatments on Gonadotropin II Levels and Ovarian Development in Juvenile Female Striped Bass (Morone saxatilis) Biol Reprod, November 1, 1998; 59(5): 1153 - 1162. [Abstract] [Full Text]