Immunocytochemical localization of relaxin in the ovaries of pregnant rats.

Relaxin was localized in the ovaries of pregnant rats by employing for the first time a highly specific rabbit anti-rat relaxin serum and the peroxidase-antiperoxidase complexing technique. The corpora lutea of pregnancy contained essentially all of the immunostaining in ovarian sections obtained on Days 12 and 20 of pregnancy. Very few cells in the corpora lutea of the previous cycle stained for relaxin. There appeared to be variation in the intensity of staining for relaxin among luteal cells on both Days 12 and 20 of pregnancy. Ovaries from nonpregnant lactating rats contained very little, if any, relaxin immunostaining. It is concluded that the corpus luteum is the principal, and, in all likelihood, the sole source of relaxin in the pregnant rat.