Triiodothyronine stimulates 3beta-hydroxysteroid dehydrogenase activity in the porcine corpus luteum.

OBJECTIVE To study the mechanism of thyroid hormone action on the activity of 3beta-hydroxysteroid dehydrogenase in the porcine corpus luteum. METHODS Pig ovaries were obtained from slaughterhouse animals. Luteal cells were isolated from mid-developing (5-7 days after ovulation) corpora lutea and incubated for 24 h with or without triiodothyronine. Trilostane, an inhibitor od 3beta-HSD that blocks the conversion of pregnenolone to progesterone, was added to the medium in doses of 0,0.1, 1, 10 and 100 micromol. Each treatment was performed in triplicate and each culture system was set up in triplicate. Progesterone concentrations in culture media were determined by radioimmunoassays. RESULTS Trilostane in a dose of 100 microM significantly decreased the basal progesterone secretion from luteal cells by 26% (P<0.05). However, such secretion was increased by triiodothyronine (T3) in a dose of 10(-9) M. In addition, in T3-treated cells dose dependent inhibitory effect of trilostane on progesterone secretion was observed. Control cultures grown in control medium revealed a relatively weak 3beta-HSD activity which, however, markedly increased after the addition of T3 to the culture medium. Trilostane remarkably decreased 3beta-HSD activity in T3-stimulated cells. CONCLUSION It was found that T3 acts on luteal cell steroidogenesis via the activation of 3beta-hydrosysteroid dehydrogenase in these cells.