Guinea-pig gonadotropin-releasing hormone: Immunoreactivity and biologicalactivity

The DNA sequence of the encoding gene predicts a unique structure for guine a-pig gonadotropin-releasing hormone (GnRH), We assessed the immunoreactivi ty of synthetic mammalian GnRH, of a synthetic peptide with predicted guine a-pig GnRH structure, and of extracts from rat and guinea-pig hypothalami, using two different RIA systems. Whereas immunoreactivity of mammalian and guineapig GnRH was rather similar when using an antiserum with conformation al specificity for mammalian GnRH (Root RR-5 antiserum), binding of both pe ptides to an antiserum with sequential specificity (Kelch R-13 antiserum) w as markedly different. The findings for GnRH extracted from rat and guinea- pig hypothalami were similar to those for the corresponding synthetic pepti des. Assessment of in-vivo biological activity of synthetic mammalian and g uinea-pig GnRH in the intact male guineapig showed that both peptides stimu late LH secretion dose-dependently, the response to mammalian GnRH being sl ightly greater at low dose. This study confirms that the GnRH expressed in the brain of the adult guinea-pig differs from mammalian GnRH and indicates that mammalian and guinea-pig GnRH display conformational similarity and t hat both can stimulate guinea-pig luteinizing hormone secretion.