Regulation of steroidogenesis in the ovine corpus luteum

To examine the factor affecting LH-induced progesterone production in vitro in ovine luteal slices, an experimental procedure was employed wherein each slice served as its own control. The role of microfilaments in steroidogenesis was studied in luteal slices treated with cytochalasin B (an inhibitor of microfilament function). Cytochalasin B treatment resulted in significant reduction of progesterone production by luteal slices in response to LH and the addition of serum to the medium did not alter this effect. The ability of luteal slices to respond to LH with increased progesterone secretion was restored when cytochalasin B was removed from the medium. Further studies indicated that inhibition of LH-induced progesterone production by treatment with cytochalasin B was not a result of a change in: 1) cyclic adenosine 3'-5'-monophosphate production in response to LH; 2) mitochondrial membrane permeability to cholesterol; or 3) activity of 3β-hydroxysteroid dehydrogenase, Δ 5,Δ 4-isomerase enzyme complex. The possibility existed that microfilaments were necessary for cholesterol transport to mitochondria in response to LH stimulation. However, mitochondrial cholesterol content was unchanged in response to LH in the presence or absence of aminoglutethimide (an inhibitor of cholesterol side-chain cleavage enzyme activity) as determined by uptake of 3H-cholesterol or total content determined by gas-liguid chromatography. Further, treatment with cytochalasin B had no effect on mitochondrial cholesterol content. These results suggest a role for microfilaments in LH-induced progesterone production at a point prior to the conversion of cholesterol to pregnenolone.