Immunocytochemical localization of relaxin in human corpora lutea: cellular and subcellular distribution and dependence on reproductive state

Relaxin is one of the hormones present during pregnancy and it is synthesized primarily by corpora lutea (CL). Other reproductive tissues including CL of the menstrual cycle may also synthesize this hormone. Very little is known, however, about the cellular and subcellular distribution of relaxin in human CL and dependence of luteal relaxin on the reproductive state. The light and electron microscope immunocytochemical studies described here were undertaken to obtain this information using antisera to porcine and human relaxin. Immunostaining was found in large luteal cells (17-30 microns) but not in small luteal cells (7-16 microns) or in nonluteal cells in any of the reproductive states or in human hepatocytes. Luteal immunostaining was low in early luteal phase; it increased progressively, reaching the highest level in late luteal phase, and then decreased greatly in corpora albicantia. Term pregnancy CL contained similar immunostaining as early luteal phase CL. Mid luteal phase CL contained more immunostained cells than late luteal phase CL, but the late luteal phase CL contained a greater amount of immunostaining per cell than mid luteal phase CL. The immunogold particles due to relaxin were primarily present in secretory granules and to a small extent in rough endoplasmic reticulum. Quantitation revealed that secretory granules contained a much higher number of gold particles than did rough endoplasmic reticulum. These two organelles from late luteal phase CL contained greater numbers of gold particles than those from mid luteal phase.(ABSTRACT TRUNCATED AT 250 WORDS)