LOCALIZATION OF SPECIFIC RELAXIN-BINDING CELLS IN THE OVARY AND TESTIS OF PIGS

It is not known whether relaxin has physiological roles in the gonads in mammalian species. Limited evidence indicates that relaxin may act locally to regulate ovarian function in pigs. The possibility of a rol e for relaxin in testicular function in pigs has not been investigated . A major initial step toward the establishment of direct effects of r elaxin on the ovary and/or testis is to demonstrate that relaxin binds with specificity to the gonads. Accordingly, the first objective of t his study was to employ an immunohistochemical localization technique to determine whether relaxin-binding cells are present in the ovaries and/or testis of pigs. Once they were found to be present, the second objective was to determine whether relaxin-binding sites noticeably ch ange either within the ovary at different stages of the estrous cycle and pregnancy, or within the testis at sexual maturity. Ovaries were c ollected from four stages of the estrous cycle (midfollicular, late fo llicular, early luteal, and midluteal) and three stages of the pregnan cy (Day 40, Day 80, and Day 110). Two gilts were used for each of the stages of the estrous cycle and pregnancy. Testes were collected from a 5-mo-old immature boar and a 36-mo-old mature boar. Tissues were cut into cubes (3-4 cm(3)), frozen in liquid nitrogen, and cryosectioned (8 mu m). Specific cell types that bind relaxin were identified by seq uential application of a biotinylated relaxin probe, antibiotin immuno globulin G conjugated to 1 nm colloidal gold, and silver for signal am plification. In the ovary, specific relaxin-binding sites were localiz ed in both the theca and granulosa cells of developing follicles, lute al cells, and blood vessels. In the testis, specific relaxin-binding s ites were localized in the Leydig cells. There were no apparent differ ences in relaxin-binding distribution within the ovary at different st ages of the estrous cycle and pregnancy in gilts, or within the testis at sexual maturity in boars. We conclude that the specific relaxin-bi nding cells within the ovary and testis of the pig may contain relaxin receptors. Therefore, relaxin may have effects in the ovary and testi s of pigs.