Thyroid hormone action in porcine luteal cells. Effect of triiodothyronine on mitochondrial cytochrome P450-scc activity.

In the present study hydroxylated cholesterol derivatives were used to monitor P450scc activity as an effect of triiodothyronine. Luteal cells isolated from mid-developing and mature corpora lutea were plated into 24-well plates by 18 h incubation with M199 supplemented with 5% of alf serum. After that time the plates were washed with fresh M199 and hydroxylated cholesterol derivatives (25-, 20-, and 22-hydroxylated cholesterol) were added to the control (not-T3-treated) and T3-treated cells. Two hours later, all cultures were terminated and the media were frozen until further progesterone analysis. Triiodotyronine added to the culture medium of cells isolated from mature corpora lutea increased both basal and hydroxylated cholesterol derivative-stimulated cells. Aminoglutethimide, a P450scc enzyme inhibitor, added to the culture medium in all doses used, had no effect on basal progesterone secretion while added to the T3-treated cells reduced progesterone production. This study strongly supports the hypothesis of a direct effect of thyroid hormone on mitochondrial cytochrome P450scc--catalysing side-chain cleavage of cholesterol enzyme in luteal cells.