Comparison of Luteinized Unruptured Follicles and Corpora Lutea: Steroid Hormone Production and Response to Luteolytic and Luteotropic Agents1

Administration of hCG prior to spontaneous ovulation induces the formation of luteinized unruptured follicles (LUFs) in guinea pigs. Serum progesterone (P) in animals with LUFs is significantly lower. This study was designed to determine whether follicular maturity affected the incidence of LUFs and P production as well as to compare isolated LUFs with corpora lutea (CL) in relation to hormone production and response to luteotropic and luteolytic agents. Ovarian histology and serum steroids following injection of hCG at various times during the estrous cycle indicated that greater follicular maturity increased the incidence of ovulation and P production. LUFs and CL contained equivalent amounts of P/mg tissue, but LUFs were significantly smaller than CL. Cells from CL and LUFs responded to hCG in vitro with significant increases in P release, but the response was greatest with LUFs. Prostaglandin F2 alpha (PGF) attenuated the response to hCG in vitro by mid-cycle CL and LUFs, but not by CL obtained during the early luteal phase. We conclude that the attenuated luteal-phase P profile following induction of LUFs is not an intrinsic deficiency in hormone production, but may arise from the smaller mass of luteal tissue and from earlier than normal development of responsiveness to the luteolytic effects of PGF.