Characterization of two steroidogenic cell types in the ovine corpus luteum.

Abstract

A procedure which utilized elutriation was developed which permitted the separation of two populations of luteal cells from enzymatically dispersed corpora lutea taken from superovulated ewes on the 10-12th day of the estrous cycle. One population consisted of cells which measured 23-35 pm in diameter, while the other consisted of cells with a diameter of 12-22 pm. Preparations of both cell types were analyzed for rate of secretion of progesterone, responsiveness to secretagogues, and number of specific binding sites for luteinizing hormone/human chorionic gonadotropin (LH/hCG), and prostaglandins E2 and F2a (PGE2 and PGF2a). Without stimulation, the secretion of progesterone by large cells was approximately 20-fold greater than for an equal number of small luteal cells. However, the ability of large luteal cells to respond to LH (100 ng/mI) or N6,02-dibutyryladenosine 3’: 5’-cyclic monophosphoric acid (dbcAMP, 10 mM) was minimal and approximately 10% of that obtained with small luteal cells. Marked differences were also observed between the two cell types with respect to the number of specific binding sites for LH/hCG, PGE2 and PGF2 a. The large cells had very few receptors for LH/hCG compared to small cells (3074 receptors/large cell vs. 33,260/small cell during the breeding season). The majority of receptors for prostaglandins was found in large cells (68,143 sites of PGF2a and 10,955 sites for PGE2/large cells; 2115 sites for PGF2a and 904 sites for PGE2/small cell). These data suggest that functional differences exist between the large and small steroidogenic cells in the corpus luteum of the ewe. The large luteal cells appear to secrete most of the progesterone produced by the corpus luteum, however, this secretion appears to be independent of LH and dbcAMP. In contrast, the small luteal cells secrete minimal quantities of progesterone in the unstimnulated state butresponddramatically to LH or dbcAMP.