Effect of aminoglutethimide phosphate on in vitro oestradiol stimulated progesterone synthesis by rabbit corpora lutea.

Slices of rabbit corpora lutea were incubated for 3 and 8 h with oestradiol-17beta in the presence or absence of aminoglutethimide phosphate (AGP) in order to identify a possible site(s) of action of oestrogen on progesterone synthesis. Oestradiol was unable to increase progesterone biosynthesis above controls in luteal tissue exposed to AGP during either incubation period. AGP alone significantly reduced progesterone concentrations and synthesis from [14C]acetate at both time periods while oestradiol alone increased progesterone mass at 8 h. Changes in 20alpha-OH progesterone typically paralleled those of progesterone at 3 h but no effect of the inhibitor was seen at 8 h. Except for an increase in 14C-incorporation into cholesterol esters in the AGP-treated groups at 3 h the concentration or synthesis of sterols from labelled acetate did not respond to treatment. These results suggested that cholesterol side chain cleavage and cholesterol synthesis are not major in vitro sites of action of oestradiol in the rabbit corpus luteum.