Guinea-pig gonadotropin-releasing hormone: immunoreactivity and biological activity

The DNA sequence of the encoding gene predicts a unique structure for guinea-pig gonadotropin-releasing hormone (GnRH). We assessed the immunoreactivity of synthetic mammalian GnRH, of a synthetic peptide with predicted guinea-pig GnRH structure, and of extracts from rat and guinea-pig hypothalami, using two different RIA systems. Whereas immunoreactivity of mammalian and guinea-pig GnRH was rather similar when using an antiserum with conformational specificity for mammalian GnRH (Root RR-5 antiserum), binding of both peptides to an antiserum with sequential specificity (Kelch R-13 antiserum) was markedly different. The findings for GnRH extracted from rat and guinea-pig hypothalami were similar to those for the corresponding synthetic peptides. Assessment of in-vivo biological activity of synthetic mammalian and guinea-pig GnRH in the intact male guinea-pig showed that both peptides stimulate LH secretion dose-dependently, the response to mammalian GnRH being slightly 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 that both can stimulate guinea-pig luteinizing hormone secretion.