Meeting Abstract
11.3 Thursday, Jan. 3 Gonadotropin-releasing hormone synthesis and release is regulated by insuline-like growth factor-1 in the teleost, Rachycentron canadum GALIMA, MM*; KHAN, IA; The University of Texas at Austin; The University of Texas at Austin galima@utmsi.utexas.edu
Reproductive development in vertebrates is centrally regulated by gonadotropin-releasing hormone (GnRH) neurons. One factor involved in the regulation of the GnRH system is the neurotrophic factor, insulin-like growth factor-1. To better understand how GnRH is regulated by IGF-1, we examined the effect of intramuscular administration of recombinant human IGF-1 (rhIGF-1; 1.0 or 10 ng/g body weight [BW]) on whole-brain seabream GnRH (GnRH) mRNA expression in pubertal cobia (Rachycentron canadum). We also examined the ability of IGF-1 to affect the release of GnRH from explanted POAH and pituitary tissue slices in pubertal fish. In vivo treatment of pubertal cobia with rhIGF-1 at 1.0 or 10 ng/g BW resulted in significant elevation of whole-brain GnRH mRNA expression after 4 hr. In addition, pituitary GnRH peptide levels in rhIGF-1 treated cobia were significantly elevated compared to controls, while GnRH peptide concentrations in POAH were unchanged. Short-term exposure of POAH and pituitary tissues from pubertal fish with rhIGF-1 (10, 50 or 100 ng/ml) stimulated GnRH release. The 100 ng/ml dose induced the maximum GnRH release from POAH slices after the first 30 min of exposure, while the pituitary continued to respond to IGF-1 in the two consecutive 30 min treatments. Taken together, the stimulatory effects of IGF-1 on GnRH mRNA synthesis in vivo, as well as GnRH release in vitro, strongly suggest that the IGF-1 peptide can exert direct effects on GnRH neurons in fish similar to the situation in mammals. Therefore, these results demonstrate that IGF-1 serves as an important signal in the regulation of the GnRH neuroendocrine pathway and may play an important role in the initiation of puberty in general. [Supported by Sid Richardson Memorial Fund & Advanced Technology Program of TX].
