Relaxin and relaxin c-peptide levels in human reproductive tissues.

A radioimmunoassay for a representative portion of the c-peptide of human relaxins (H1 and H2) was developed and validated. Relaxin c-peptide is present in preprorelaxin and prorelaxin, and exists free after the maturation of relaxin is completed. The aim of the study was to identify possible production and storage sites of human relaxin by comparing c-peptide and relaxin levels in various human reproductive tissues. c-Peptide immunoreactivity was present in the corpus luteum, amniochorion, decidua and seminal plasma; this indicates that these tissues may be relaxin production sites. Relaxin was detected in the corpus luteum, amniochorion, decidua, trophoblast, seminal plasma, myometrium and fibroids. This suggests that these tissues are storage and/or target sites for relaxin. The highest concentration of relaxin was detected in decidua at term. This level decreased after labour. The concentrations of c-peptide and relaxin were approximately equimolar in serum during pregnancy. This study lends support to the concept that relaxin is produced and stored at extra-luteal sites; these sites of hormone production support a paracrine role for relaxin during pregnancy.