ISOLATION OF A HUMAN SEMINAL PLASMA PEPTIDE WITH BOMBESIN-LIKE ACTIVITY

Bombesin (BN) and BN-like peptides such as gastrin-releasing peptide (GRP) belong to the growing group of regulatory peptides. Bombesin and GRP share the same carboxylterminal heptapeptide sequence that is essential for receptor recognition and biologic activity. Immunohistochemical findings have indicated the presence of a BN-like peptide in the neuroendocrine cells of the human prostate. These findings, together with the high concentrations of different regulatory peptides recently found in seminal plasma, prompted us to characterize a BN-like peptide in human semen by gel-filtration chromatography, reverse-phase high-pressure liquid chromatography, and in vitro bioassay. Here we demonstrate that human semen contains high levels (mean ± standard deviation, 288.9 ± 114.39 pg/ml) of a substance that closely resembles the 14-27 carboxyl-terminal fragment of GRP (GRP 14-27). The partially purified peptide obtained from this source, examined on an in vitro bioassay that is especially useful for testing BN-like activities, elicits a contractile response of the rat uterus that is indistinguishable from that stimulated by standard BN and GRP 14-27. The GRP 14-27 present in human seminal plasma may be involved in some aspect of the process of fertilization.