Immunohistochemical demonstration of relaxin in the placenta after removal of the corpus luteum.

We studied the occurrence of relaxin in the term placenta from a woman who had normal pregnancy after her corpus luteum had been removed at the beginning of the second trimester. Two antisera (antiserum R6 and anti-NIH-RXN-P1. 3000 U/mg) against highly purified porcine relaxin and the avidin-biotinylated anti-rabbit IgG method were used to detect relaxin-like immunoactivity. Specific staining for relaxin was seen in the placental syncytiotrophoblasts. Comparison to a placenta from a normal term delivery revealed no differences in the intensity or distribution of staining. Our case substantiates that the corpus luteum is not the only tissue producing relaxin during pregnancy.