Further evaluation of the biological activity of the unique gonadotropin-releasing hormone peptide in the guinea pig brain

In this study we compared the biological activity of a unique form of gonadotropin-releasing hormone (GnRH) in the brain of the guinea pig (gpGnRH) with mammalian GnRH (mGnRH). In gpGnRH, the highly conserved histidine in position 2 (His2) and leucine in position 7 (Leu7) are substituted by tyrosine and valine, respectively. The gpGnRH was less potent than mGnRH in stimulating the release of luteinizing hormone (LH) in vivo in the guinea pig and displayed only low activity in the rat. The gpGnRH was more rapidly degraded by serum proteolytic enzymes than mGnRH. It is concluded that gpGnRH displays lower biological activity than mGnRH in both rat and guinea pig, which may be due in part to its greater susceptibility to proteolytic degradation besides differences in receptor affinity and/or activation.

Research highlights▶ Guinea pig GnRH is unique in its structure. ▶ Guinea pig GnRH was significantly less potent than mammalian GnRH in vivo. ▶ Guinea pig GnRH was degraded more rapidly in serum than mammalian GnRH. ▶ The lower activity of guinea pig GnRH is explained at least in part by a greater susceptibility to degradation in serum.