19-Hydroxylation of androgens by rat granulosa cells

The transformation of androgens by rat granulosa cells was examined employing [19-C3H3]-, [1 beta-3H]-, and [1,2,6,7-3H]androgens as substrates. Rat granulosa cell homogenates incubated with [19-C3H3]androstenedione generated [3H] water and [3H]formic acid in a ratio of 8-9, indicating considerable 19-hydroxylation which was not followed by aromatization. This ratio remained relatively constant regardless of the time in the estrous cycle when the ovaries were removed, although there were large differences in the extent of the reactions. Parallel incubations with [1 beta-3H]]androstenedione showed that the aromatization of [19-C3H3]androstenedione in this tissue proceeds with a negative isotope effect of approximately 3, similar to that in human placenta. Incubation of the same substrates with granulosa cell cultures produced [3H]water and [3H]formic acid in ratios of 4-5 and showed a smaller negative isotope effect in the aromatization of [19-C3H3]androstenedione. FSH stimulation of the cell cultures had no influence on the ratio of 19-hydroxylation to aromatization with respect of either the duration of stimulation or the concentration of the pituitary hormone. Incubation of the cell cultures with [1,2,6,7-3H]androstenedione yielded tritium-labeled 19-hydroxy- and 19-oxoandrostendiones and estrogens in relative quantities corresponding to those expected from the [3H]water and [3H]formic acid formation. Virtually all of the products were found in the medium, with only trace quantities located intracellularly. Similarly, incubation of granulosa cell homogenates with [14C]androstenedione yielded [14C]19-oxygenated androgens in excess of [14C] estrogens. These results indicate that rat granulosa cells effect C-19-hydroxylation of androgens greater than that linked to aromatization and that the rat ovaries produce 19-oxygenated androgens in quantities exceeding those of estrogens. The excess 19-hydroxylation is synchronous with aromatization, but it is not known whether it is catalyzed by the same or a different enzyme. The formation of 19-oxygenated androgens in cell cultures indicates that they are distinct metabolites of androgens in the rat ovary and are not merely trapped transient aromatization intermediates.