STEROIDOGENIC ENZYME-ACTIVITY AFTER ACUTE ACTIVATION OF PROTEIN-KINASE (PK) A AND PKC IN OVINE SMALL AND LARGE LUTEAL CELLS

Intracellular effector systems which utilize PKA and PKC can be pharma cologically activated by forskolin and phorbol 12-myristate 13-acetate (PMA) and appear to be important for regulation of steroidogenesis by cells of the corpus luteum. In this study the effect of pharmacologic activation of PKA (forskolin) or PKC (PMA) on the activity of adenyla te cyclase, cholesterol esterase, P450 cholesterol side chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase/Delta 5,Delta 4 iso merase (3 beta HSD) was determined. Basal adenylate cyclase activity ( as measured by intracellular and secreted cAMP) was extremely low in b oth large and small luteal cells. Forskolin stimulated adenylate cycla se activity in both large and small luteal cells but progesterone prod uction was increased only in small cells. PMA inhibited progesterone p roduction by large and forskolin-stimulated small cells without alteri ng adenylate cyclase activity. Basal cholesterol esterase activity was greater in small than in large cells and was stimulated by forskolin only in small cells. PMA did not significantly alter cholesterol ester ase activity in either cell type. Activity of P450scc or 3 beta HSD wa s measured by conversion of hydroxylated cholesterol derivatives (P450 scc) or pregnenolone 3 beta HSD) to progesterone. Although basal proge sterone production was 47 times greater in large than small cells, the re was only 5.1 (P450scc) and 6.4 (3 beta HSD) times greater enzyme ac tivity in large than in small luteal cells, Activation of PKA and/or P KC did not alter the activity of P450scc or 3 beta HSD in either cell type. In conclusion, it appears that the difference in basal progester one production between the small and large cells cannot be completely explained by differences in adenylate cyclase, cholesterol esterase, P 450scc or 3 beta HSD enzyme activity. In addition we found that the on ly steroidogenic enzyme acutely regulated by PKA or PKC was cholestero l esterase which was stimulated by PKA in small cells.