Fertilization-promoting peptide: a novel peptide, structurally similar to TRH, with potent physiological activity

Abstract

Introduction Thyrotrophin-releasing hormone (TRH) was the first of the hypothalamic releasing hormones to be characterised in the late 1960s, and was soon observed throughout the central nervous system (CNS) and in several peripheral tissues (for review, Hokfelt et al. 1989). Some time later, reports started to appear of unusual immunoreactivity which suggested the existence of peptides differing from TRH (pGlu-His-ProNH2) by the central amino acid: i.e. with the structure pGlu-Xaa-ProNH2, where Xaa is an unknown amino acid. The first of these TRH-related peptides to be identified was fertilization-promoting peptide (FPP) (Xaa: Glu) (Fig. 1), followed by three further peptides containing Phe, Gln or Tyr as the previously unknown amino acid (for review, Ashworth 1994). To date, FPP is the only TRH-related peptide known to have a definitive physiological role (Green et al. 1994). Distribution of FPP FPP occurs in high concentrations in rabbit prostate with low to undetectable