Meeting Abstract

S6-1.4  Saturday, Jan. 5  Mechanisms of Action of Gonadotropin-inhibitory hormone in birds and mammals UBUKA, T*; BENTLEY, GE; Univ. of California, Berkeley ubukat@berkeley.edu

Gonadotropin-releasing hormone (GnRH) is one of the primary factors responsible for the hypothalamic control of gonadotropin secretion; gonadotropin inhibitory hormone (GnIH) is another. GnIH homologs are present in the brains of many vertebrates, including birds, mammals, amphibians and fish. These peptides, categorized as RFamide-related peptides (RFRPs), possess a characteristic LPXRF-amide (X = L or Q) motif at their C-termini. GnIH mRNA encodes a precursor polypeptide that is possibly cleaved into 3 mature peptides in birds and 2 mature peptides in mammals. These peptides have been named GnIH and GnIH-related peptides-1 and -2 in birds, and RFRP-1 and -3 in mammals. GnIH precursor is located in neurons of the paraventricular nucleus in birds and dorsomedial hypothalamic area in mammals. GnIH neurons project to the median eminence, thus providing a functional neuroanatomical infrastructure to regulate anterior pituitary function. GnIH immunoreactive axon terminals are also in probable contact with GnRH neurons in birds and mammals. We have recently found that GnIH receptor mRNA is expressed in GnRH-I and -II neurons in European starlings. Thus, GnIH might be an important factor for the regulation of GnRH, in addition to having direct actions upon the pituitary gland. We used a cultured gonadotrope cell line to determine the cellular mechanisms of action of GnIH and its related peptides upon gonadotropin release. Our results suggest that GnIH and its related peptides act differentially to influence gonadotropin synthesis and release, respectively. In sum, our data indicate that GnIH and its related peptides are important modulators of reproductive function at the level of the gonadotrope and the GnRH neuron.