Participation of the cytoskeleton in avian granulosa cell steroidogenesis.

Cytochalasin B (CB) and the more specific cytochalasin D (CD), disruptors of microfilament polymerization, and colchicine, an inhibitor of microtubule polymerization, were studied for their effects on cAMP and steroid production in granulosa cells of domestic fowl. Each agent was incubated with freshly dispersed cells from the largest preovulatory follicle of laying hens taken 3-4 hr before expected ovulation. Total content (cells + medium) of cAMP and steroids was measured by established radioimmunoassays. CB dose dependently inhibited basal as well as LH- and forskolin-stimulated cAMP generation and diminished basal, LH- and 25-hydroxycholesterol (25-OHC)-supported progesterone production. Conversely, CD potentiated LH- and forskolin-promoted cAMP generation as well as LH- and 25-OHC-stimulated progesterone synthesis. Neither drug had any influence on metabolism of pregnenolone to progesterone. Colchicine had no effect on cyclic AMP generation, yet it suppressed progesterone synthesis by inhibiting the conversion of pregnenolone to progesterone. beta-Lumicolchicine, a colchicine analog that does not depolymerize microtubules, had no such effect. The results suggest that microfilaments are involved in steroidogenesis at two sites, namely, the adenylate cyclase-cAMP system, and cholesterol conversion to pregnenolone; whereas microtubules act on the conversion of pregnenolone to progesterone.