Relaxin in Human Decidua and Term Placenta

Using both a homologous porcine RIA and 3 bioassays, we investigated the relaxin content of human decidua from first trimester and term gestations and of placentas at term. Aqueous extracts of these tissues yielded only between 211 and 1090 pg immunoreactive relaxin/g fresh tissue. Neither acetonehexane extraction, octadecylsilica cartridge elution nor molecular sieve chromatography increased these relaxin levels. Compared with term decidua, first trimester decidua contained significantly higher levels of immunoreactive relaxin. In vitro studies did not evidence significant relaxin production by either decidual or placental tissues, even in the presence of decidual prolactin production. These results are in direct contrast to earlier reports of high concentrations of relaxin in decidua and placenta.