PKCepsilon and an increase in intracellular calcium concentration are necessary for PGF2alpha to inhibit LH-stimulated progesterone secretion in cultured bovine steroidogenic luteal cells

PKCepsilon expression was reduced 65 and 75% by 72 and 96 h after transfection, respectively. In cells in which PKCepsilon expression was ablated by 75%, the inhibitory effect of PGF2alpha on LH-stimulated P4 secretion was only 29% lower than in the LH-stimulated group. In contrast, it was reduced by 75% in the group where PKCepsilon expression had not been reduced (P < 0.05). Real time PCR analysis indicated that there were no differences in the expression of cyclooxygenase-2 (COX-2), aldoketoreductase 1B5 (AKR1B5), prostaglandin E synthase (PGES), hydroxyprostaglandin-15 dehydrogenase (PGDH) and PGE2 -9-reductase as a function of PKCepsilon down-regulation. Finally, LH stimulated secretion of P4 at each luteal stage (Day -4 and -10), and PGF2alpha inhibited this only in Day -10 cells (P < 0.05). When A23187 was used at concentrations greater than 0.1 μmol, the induced elevation in [Ca(2+)]i inhibited the effect of LH on secretion of P4 in Day -4 and -10 cells (P < 0.05, Fig. 5). The inhibitory effect of PGF2alpha on LH-stimulated P4 in Day -10 cells was reduced if an increase in [Ca(2+)]i was prevented with Bapta-AM. These results support the hypothesis that differential expression of PKCepsilon and an elevation of [Ca(2+)]i are important for acquisition of luteolytic response to PGF2alpha.The corpus luteum (CL) is a transient endocrine gland whose primary secretory product is progesterone (P4). The life span of the CL and consequently the amount of P4 it secretes is regulated according to reproductive physiological status. Substances reducing P4 secretion and shortening the luteal life span are said to be luteolytic [1,2].In most species, including human beings, PGF2α is recognized as an important if not the main luteolytic factor [3-9]. During the ovarian cycle, the transition from early to mid-luteal phase is associated with changes in resistance/susceptibility to the luteolysin PGF2α; in cows, the CL is resistant to exogenous PGF2α prior to day 5 of the estrou