INDO, a COX inhibitor, did not affect cell viability, Dovitinib cancer but significantly decreased LH-induced cell viability to the control level. The viability of cells treated with INDO in combination with LH was not significantly different from the viability of cells treated with INDO alone (Fig. 4A; P<0.05). Fig. 4. (A) Effects of LH and/or INDO on cell viability. (B) Effects of LH and/or INDO on PGF production. (C) Effects of LH and/or INDO on P4 production. The cells were treated with LH (10 ng/ml) alone or in combination with INDO (100 ��M) for 24 h. Cell viability ... LH significantly increased PGF production. INDO did not affect basal PGF production, but significantly decreased LH-increased PGF production to the control level (Fig. 4B; P<0.05). LH significantly increased P4 production.

INDO did not affect basal and LH-stimulated P4 production (Fig. 4C; P<0.05). Discussion LH is an important regulator of ovarian function. The main role of LH in bovine luteal cells is to stimulate P4 secretion, which suppresses apoptosis of these cells [5]. LH also strongly stimulates P4 production by cultured bovine luteal cells [26]. Thus, although LH seems to play a luteoprotective role by stimulating P4 production, the other luteoprotective roles of LH in bovine luteal cells have not been well understood. In fact, LH increased the viability of luteal cells in vitro in the present study. Although we previously demonstrated that PGF and PGE2 as well as P4 play anti-apoptotic roles in the bovine CL [5, 11], it is not known whether LH increases cell viability by regulating survival factors, such as P4 and PGs.

At first, to confirm the luteoprotective action of LH is mediated by P4 in the present study, onapristone (OP: a specific P4 receptor antagonist) was used to inhibit the action of P4 on cell viability. OP decreased LH-induced cell viability, indicating that one of the means of CL protection by LH is mediated by P4. On the other hand, LH rescued the decrease in cell viability caused by OP, suggesting that a mechanism other than P4 stimulation is induced by LH to rescue cell viability. cAMP, which acts as a primary second messenger of LH action, has important roles in many biological processes through cAMP-dependent kinase (PKA) and/or in a PKA-independent manner [27,28,29]. In addition, cAMP analogues were found to act as anti-apoptotic agents not only in bovine luteal cells but also in non-steroidogenic cells [30, 31].

These findings support our suggestion that LH increases luteal cell viability by a mechanism other than P4 stimulation. In many cell types including luteal cells, apoptosis is mediated by death receptors, such as FAS [32,33,34], and by many intracellular regulators, such as caspases (CASPs) [35, 36]. FAS is a receptor of the tumor necrosis AV-951 factor �� superfamily and is activated by binding to FAS ligand, leading to receptor aggregation and apoptotic signal transmission [32,33,34].