Steroid Metabolism in Theca Externa Cells from Preovulatory Follicles of Domestic Hen (Gallus domesticus)

Abstract

The purpose of this study was to evaluate the ability of theca externa cells from preovulatory follicles of the domestic hen to metabolize tritiated steroid precursors. Theca externa cells were isolated from ovarian preovulatory follicles at three different developmental stages; F1 (35 mm), F3 (26 mm), and F5 (13 mm). Tritiated pregnenolone (P5), progesterone (P4), dehydroepiandrosterone (DHEA), androstenedione (A4), and testosterone (T) were employed as precursors and their metabolic products were evaluated after separation by thin-layer chromatography. The major metabolite of P5 by theca externa cells was 5-pregnen-3β,20β-diol (F5, 47%; F3, 39%; and F1, 24%), but minimal quantities of P4 were detected. Progesterone metabolism yielded mainly 4-pregnen-20β-ol-3-one (F5, 52%; F3, 34%; and F1, 49%). When DHEA was used as precursor, A4 was produced in higher amounts (F5, 29%; F3, 23%; and F1, 11%) than estrone (E1) (F5, 1.5%; F3, 0.9%; and F1, 0.4%). Androstenedione was mainly transformed into E1 (F5, 11.9%; F3, 12.2%; and F1, 0.2%), but lower quantities of T and 17β-estradiol (E2) were found. Testosterone was actively transformed into A4 (F5, 50%; F3, 50%; and F1, 30%), but a low transformation to E2 (F5, 1.9%; F3, 1.7%; and F1, 1.4%) and E1 (F5, 2%; F3, 1%; and F1, 0.5%) was found. These results show that theca externa cells from preovulatory follicles of hen have enzymatic activities of 20β-reductase (from P5 and P4), 3β-hydroxysteroid dehydrogenase/5-4 isomerase (from P5 and DHEA), 17β-hydroxysteroid dehydrogenase (from A4 and T), and aromatase (from A4 and T). Furthermore, the enzyme activities decrease with follicular maturation, except for 20β-reductase which is constant. These data support the concept that theca externa cells have the ability to synthesize different steroids than reported in theca externa cells. In addition, since theca externa cells did not show the capacity to produce androgens but these steroids were aromatized to estrogens by these cells, it was suggested that the interaction between theca interna cells and theca externa cells occursin vivo,thus supporting the multicellular theory for estrogen production.