Establishment and clinical application of enzyme immunoassays for determination of luteinizing hormone releasing hormone and metastin.

Metastin, a 54-residue peptide, was identified as the cognate ligand of human G-protein-coupled receptor GPR54. Since metastin is a gene product of the human metastasis suppressor gene 'KiSS-1', early studies on metastin were focused on its activity as a tumor metastasis suppressor. Recently, there have been some reports that metastin is found in human plasma and is particularly abundant in the plasma of pregnant women. Dysfunction of the GPR54 receptor causes diseases that are characterized by an insufficient release of gonadotropin and lack or delay of pubertal maturation. This information strongly suggests that metastin is involved in the regulation of reproductive endocrine functions. In order to determine the plasma levels of metastin and luteinizing hormone releasing hormone (LHRH) in an isolated hypogonadotropic hypogonadism (IHH) patient, who received intermittent administrations of LHRH, we tried to establish a sensitive and specific enzyme immunoassay. The plasma LHRH levels of the patient were very high, while plasma metastin levels were at almost the same levels as circadian rhythms of healthy male humans. In the central nervous system, metastin stimulates the neuroendocrine reproductive axis. However, the effects of peripheral metastin are not known. Our result suggested that peripheral metastin had a genesis and activity different from central metastin.