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Biology of Reproduction 66, 1604-1611 (2002)
© 2002 Society for the Study of Reproduction, Inc.

Regular Article

Gonadotropin-Releasing Hormone Does Not Directly Stimulate Luteinizing Hormone Biosynthesis in Male African Catfish1

F.E.M. Rebers3,a, G.A.M. Hassinga, W. van Dijka, E. van Straatena, H.J.Th. Goosa, and R.W. Schulz2,a

a Utrecht University, Faculty Biology, Research Group Endocrinology, NL-3584 CH Utrecht, The Netherlands

Besides gonadotropin release, GnRH stimulates gonadotropin subunit gene transcription and translation in gonadotrophs. In the African catfish, Clarias gariepinus, chicken GnRH-II (cGnRH-II: [His5,Trp7,Tyr8]-GnRH) and catfish GnRH (cfGnRH: [His5,Asn8]-GnRH) are two endogenous forms of GnRH. Studying their effects on LH subunit steady-state mRNA levels, LH de novo synthesis, and LH release in primary pituitary cell cultures of adult males, we found that cGnRH-II hardly influenced the steady-state levels of LH subunit mRNAs or LH de novo synthesis, although it stimulated LH release. Although cfGnRH stimulated LH secretion as well, high concentrations—although apparently still within the physiologic range—reduced LH transcript levels and de novo synthesis in primary pituitary cell cultures. In vivo experiments demonstrated a biphasic response of LH subunit transcript levels after a single GnRH injection: a decrease after 2 h was followed by an increase at 8 h. When the testes were removed before GnRH treatment, however, LH transcript levels remained depressed at 8 h after GnRH injection, indicating that the secondary increase in LH transcript levels depends on the presence of the testes. We conclude that the up-regulation of LH production subsequent to GnRH stimulation in adult male African catfish is mediated by factors originating from the testis. Previous work suggests that aromatizable androgens may play an important role in this context. Under the present experimental conditions, however, GnRHs had no, or an inhibitory, direct effect on LH production in catfish gonadotrophs.

First decision: 18 September 2001.

1 This study was supported by grant 980526165 from the Dutch National Science Foundation to R.W.S.

2 Correspondence: R.W. Schulz, Utrecht University, Faculty Biology, Research Group Endocrinology, Kruyt building, Room Z-211, Padualaan 8, NL-3584 CH Utrecht, The Netherlands. FAX: 31 30 2532837; r.w.schulz{at}bio.uu.nl

3 Current address: Department of Experimental Hematology, Central Laboratory for Blood Transfusion, Amsterdam, The Netherlands






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