Relative roles of theca and granulosa cells in ovarian follicular steroidogenesis in the amphibian, Rana nigromaculata.

Using frog ovarian follicles in vitro we assessed the role of the theca/epithelium (THEP) layer and granulosa cells in the production of steroids. The THEP layer and granulosa cell-enclosed oocytes (GCEOs) were separated from ovarian follicles of the frog, Rana nigromaculata, by microdissection. Intact follicles (IFs), THEP layer, or GCEOs were cultured for 6 hr in amphibian Ringer's in the presence or absence of various steroid precursors (100 ng/ml) or of frog pituitary homogenate (FPH, 0.05 gland/ml). The amounts of progesterone (P4), 17 alpha-hydroxyprogesterone (17 alpha-OHP4), androstenedione (AD), testosterone (T), and estradiol (E2) secreted into the medium by the different types of follicular components during culture were measured by radioimmunoassay. Addition of pregnenolone resulted in a marked increase in P4 concentrations produced by GCEOs (1858 pg/follicle) and IFs (1549 pg/follicle), but a much smaller increase in P4 occurred in the THEP layer (427 pg/follicle). Likewise, addition of P4 stimulated greater production of 17 alpha-OHP4 by GCEOs (659 pg/follicle) and by IFs (877 pg/follicle) than by the THEP layer (330 pg/follicle). Exogenous 17 alpha-OHP4 markedly increased AD levels secreted by GCEOs (1139 pg/follicle) and by IFs (841 pg/follicle), but not by the THEP layer (< 15 pg/follicle). In contrast, AD addition resulted in the secretion of markedly elevated levels of T by the THEP layer (2326 pg/follicle) and IFs (3652 pg/follicle) as compared to the GCEOs (408 pg/follicle). Addition of T markedly increased E2 concentrations produced by GCEOs (378 pg/follicle) and by IFs (673 pg/follicle), but not by the THEP layer (< 12 pg/follicle).(ABSTRACT TRUNCATED AT 250 WORDS)