The steroidogenic ability of various cell types of the equine ovary

The fully developed follicular wall consisting of theca interna and granulosa cells after antrim formation, granulosa cells alone, corpus hemorrhagicum, corpus luteum, corpus albicans and stromal tissue were collected from ovaries of different mares. All cell preparations were incubated with progesterone-4- 14 C and some were also incubated with 17-hydroxyprogesterone-4- 14 C androstenedione-4- 14 C or testosterone-4- 14 C to study the relative activities of the different enzymes involved in the biosynthesis of estrogens from progesterone. Because of the differences in amount of extracellular fluid and connective tissue the yields of the different metabolites were expressed per mg DNA as well as per unit weight of tissue. The follicular walls showed active 17α-hydroxylase, 17,20-lyase, 17β-dehydrogenase and aromatizing enzyme systems. Granulosa cells alone showed a similar pattern except that the aromatizing system did not seem to be proportionately as active. The recently ovulated corpus hemorrhagicum showed high 17α-hydroxylase, 17,20-lyase and 17β-dehydrogenase activities but little aromatizing activity, while the corpora lutea showed 17α-hydroxylase and (17-hydroxyprogesterone)-20-oxido-reductase activities but low 17,20-lyase and no measurable formation of estrogens. When androstenedione or testosterone were substrates, both follicular walls and corpora lutea produced estrogens in similar amounts; the decreased lyase activity in the luteal cells, therefore, appears to account for the lack of estrogen production from C 21 precursors.