THE EFFECT OF MICROTUBULE AND MICROFILAMENT-DISRUPTING DRUGS ON PROLACTIN-STIMULATED PROGESTERONE SYNTHESIS AND SECRETION BY CULTURED PORCINE THECA CELLS

The effect of microtubule- and microfilament-disrupting drugs (colchic ine, cytochalasin B and D) on basal and prolactin (Prl)-stimulated pro gesterone synthesis and secretion was studied. Microtubures were visua lized immunocytochemically using a monoclonal antibody against the alp ha-subunits of tubulin, while microfilaments were detected using a pol yclonal antibody against actin. The second antibody was conjugated wit h FITC. Progesterone, androgen and estradiol concentration were detect ed in tissue and culture medium by appropriate radioimmunoassays. In P rl-treated cultures microtubules formed a network with more radial org anisation than in the controls. After colchicine-treatment the cells w ere round, regular in shape and microfilaments were disintegrated and replaced by punctate aggregates. Actin filaments formed typical stress fibers in theca cells (Tc). In Prl-treated cells some microfilaments were broken resulting in a diffuse immunofluorescent pattern. After tr eatment with cytochalasin B and D many of the stress fibers disappeare d, the cells became rounded and diffuse microfilaments were seen. Prl added to the culture medium increased synthesis of all investigated st eroids and additionally stimulated progesterone secretion. Exposure of theca cells to colchicine caused an increase of basal progesterone se cretion into the incubation medium which simultaneously decreased the steroid content in the cells. Colchicine suppressed Prl-stimulated syn thesis of all three steroids studied and did not have any effect on th eir secretion. Exposure of theca tissue to cytochalasin B increased ba sal progesterone and androgen synthesis but drastically decreased basa l estradiol synthesis by these cells. The opposite effect was observed after the addition of cytochalasin D, when estradiol synthesis increa sed and progesterone and androgen synthesis by theca cells was not aff ected. Microtubule and microfilaments-disrupting drugs had no effect o n the secretion of the investigated steroids in Prl-treated cells. Our results suggest that microtubules and microfilaments are involved in Prl-stimulated steroid synthesis but not in steroid secretion.