Human chorionic gonadotropin localization and morphometric characterization of human granulosa-luteal cells obtained during in vitro fertilization cycles.

The area and cytoplasmic-to-nuclear ratio (C/N) of cells aspirated from follicles with mature oocytes was determined using a computerized image analysis system. The presence of human chorionic gonadotropin (hCG) on the surface membrane and/or within the cytoplasm of each cell also was determined using a horseradish peroxidase immunocytochemical procedure. Based on morphometric characteristics, follicular cells were classified as granulosa or luteal. Granulosa cells were less than 75 micron 2 in area with a C/N of approximately 0.5. Luteal cells were classified as small (less than 75 micron 2, C/N approximately 1.5), midluteal (76 to 100 micron 2, C/N greater than 1.5) and large luteal (greater than 100 micron 2, C/N greater than 1.5). Compared with aspirates from follicles containing fertilizable oocytes, aspirates from follicles with nonfertilizable oocytes had fewer granulosa cells and more large luteal cells. HCG was localized on the membranes of granulosa and small luteal cells and within the cytoplasm of midluteal cells. Human chorionic gonadotropin was generally not observed on either the membranes or cytoplasm of luteal cells over 120 micron 2. These data support the concept that granulosa cells bind hCG to membrane receptors, internalize hCG, and begin to luteinize in response to hCG stimulation. Since the aspirates from follicles containing nonfertilizable oocytes possessed a higher percentage of large luteal cells, it is postulated that the cells from these aspirates began the luteinization process earlier than those from follicles containing fertilizable oocytes.