LOCALIZATION OF STEROIDOGENIC ENZYMES IN MACAQUE LUTEAL TISSUE DURINGTHE MENSTRUAL-CYCLE AND SIMULATED EARLY-PREGNANCY - IMMUNOHISTOCHEMICAL EVIDENCE SUPPORTING THE 2-CELL MODEL FOR ESTROGEN PRODUCTION IN THEPRIMATE CORPUS-LUTEUM

It is hypothesized that the two-cell model for estrogen production by the ovarian follicle is preserved in the primate corpus luteum, but th ere is little direct evidence to support this theory. To determine the sites of androgen and estrogen synthesis within the primate corpus lu teum and to ascertain whether changes in steroid hormone levels are re lated to steroidogenic enzyme expression, the enzymes converting proge sterone to androgen (cytochrome P4501 17 alpha-hydroxylase/17,20 lyase ; P450(c17)) and then to estrogen (aromatase; P450(arom)), as well as P450 side-chain cleavage (P450(scc)) and 3 beta-hydroxysteroid dehydro genase (S beta HSD), were detected by immunohistochemistry in macaque luteal tissue throughout the menstrual cycle and simulated early pregn ancy. Corpora lutea were collected from rhesus monkeys in the early (D ays 2-4 post-LH surge), mid (Days 6-8), mid-late (Days 10-12), and lat e (Days 14-15) luteal phase and after 1, 3, 6, or 9 days of hCG treatm ent that began on Day 9 of the luteal phase. Specific cytoplasmic stai ning for P450(c17), P450(arom), P450(scc/) and 3 beta HSD was present in luteal cells, but not in the microvasculature, within all luteal ti ssues examined. P450(c17)-stained luteal cells were located along the vascular tracts and around the periphery of the corpus luteum. Intense ly stained luteal cells were associated with blood vessels entering fr om the outer surface of the corpus luteum, but not with blood vessels returning from the connective tissue centrum. In contrast, P450(arom)- stained luteal cells were distributed throughout the luteal parenchyma . P450(c17) staining intensity was similar at all stages of the luteal phase; however, the number and intensity of P450(arom)-stained cells decreased by late luteal phase. In simulated early pregnancy, cells st ained for P450(c17) were present near blood vessels, with some positiv e cells scattered throughout the corpus luteum. P450(arom) immunostain ing was heterogeneous within the corpus luteum; many intensely stained cells were interspersed among others that were only lightly stained. Overall, cellular staining for P450(c17) and P450(arom) remained inten se through 9 days of simulated early pregnancy. In contrast, P450(scc) and 3 beta HSD immunoreactivity were not located in distinct luteal c ompartments. These results are consistent with a two-cell model for st eroid hormone production in the primate corpus luteum, whereby paralut eal (theca-luteal) cells produce androgen substrate that is converted to estrogens by true (granulosa-) luteal cells. The divergence in enzy me detection as the luteal phase progresses, with P450(c17) labeling h igh and P450(arom) staining having decreased, suggests a shift in the function of the corpus luteum as it ages. Enzyme localization during c horionic gonadotropin exposure simulating early pregnancy demonstrates the continued capacity of the primate corpus luteum to produce steroi d hormones.