PROSTAGLANDINS MEDIATE THE STIMULATION OF DEOXYRIBONUCLEIC-ACID SYNTHESIS BY TRANSFORMING GROWTH-FACTOR-ALPHA IN HEN GRANULOSA-CELLS DURING OVARIAN FOLLICULAR DEVELOPMENT

The present study was an examination of the possible involvement of specific membrane lipid metabolites of prostaglandins (PGs), leukotrienes (LTs), lysophosphatidic acid (LPA), and lysophophatidyl choline (LPC) in transforming growth factor alpha-(TGF alpha) induced DNA synthesis by granulosa cells during follicular development. Granulosa cells from the first (F1) and the fifth and sixth (F5-6) largest preovulatory follicles were cultured for 18 h in the presence of TGF alpha and/or an inhibitor of either phospholipase A(2) (PLA(2)), cyclooxygenase, or lipoxygenase, LTs, LPA, LPC, and/or PGs. TGF alpha-induced, but not basal, DNA synthesis in F1 and F5-6 granulosa cells was suppressed by inhibitors of PLA(2) and cyclooxygenase but not of lipoxygenase. The inhibition was concentration-dependent and could be attenuated by exogenous PGE(2). Likewise, PGF and PGE production was suppressed by these inhibitors. Moreover, PGE(2) and, to a lesser extent, PGF(2 alpha) increased basal [H-3]thymidine incorporation and enhanced DNA synthesis induced by a submaximal stimulatory concentration of TGF alpha. The mitogenic effect of PGs was more evident in granulosa cells from F5-6 follicles than in those from Fl follicles. In contrast, LTs (LTB(4), LTC(4), LTD(4)), (+)5(s)-hydroxy-(6E,8Z,11Z,14Z)-eicosatetraenoic acid (5-HETE), and lysophospholipids (LPA and LPC) had no effect on granulosa cell DNA synthesis, irrespective of the stage of ovarian follicular development and the presence of TGF alpha and PGE(2). These studies demonstrate that 1) arachidonic metabolites of cyclooxygenase, but not lipoxygenase pathway and arachidonate lysophospholipid; by-products (LPA and LPC), are involved in the regulation of granulosa cell DNA synthesis by TGF(alpha; 2) compared to PGs of the F series, PGE(2) and PGE(1) are more effective in either mimicking the action of TGF alpha or potentiating the mitogenic response of the cells to the growth factor; and 3) the DNA synthetic response of the hen granulosa cell to PGs is greater in granulosa cells from F5-6 than in those from FI follicles. These findings are consistent with our concept that an increase in PG production is a necessary element in the TGF alpha-regulated cascade of biochemical events leading to chicken granulosa cell mitogenesis during hen ovarian follicular development.