Immunohistochemical localization of relaxin-like factor/insulin-like peptide-3 in the bovine corpus luteum.

: Relaxin-like factor/insulin-like peptide (INSL)-3 is highly expressed in the bovine corpus luteum throughout the estrous cycle and pregnancy. Demonstration of translation of the relaxin-like factor message was previously shown for the follicle but not the corpus luteum. In this study, relaxin-like factor mRNA was highly expressed in the corpus luteum on days 7 and 14 of pregnancy. Tissues were fixed in 10% neutral buffered formalin, and utilizing two different antibodies to relaxin-like factor, W3 rabbit anti-bovine and 2-8F mouse anti-bovine, relaxin-like factor was localized in fibroblast-like cells. Staining was also observed in the Leydig cells of bovine testicular tissue. No staining was observed in small and large steroidogenic luteal cells, indicating a nonsteroidogenic source of luteal relaxin-like factor. Definitive cell type identification is currently being determined via electron microscopy.