The expression of Steroidogenic Factor-1 and its role in bovine steroidogenic ovarian cells during the estrus cycle and first trimester of pregnancy.

The orphan receptor Steroidogenic Factor-1 (SF-1, NR5A1), a member of the nuclear receptor superfamily, is present in fetal and adult steroidogenic tissues and also participates in the regulation of ovarian function. In this study, the expression levels of SF-1 mRNA and protein were determined in granulosa cells (from follicles >1cm and <1cm in diameter) and luteal tissue (from days 1-5, 6-10, 11-15, and 16-19 of the estrous cycle and weeks 3-5, 6-8, and 9-12 of pregnancy). Additionally, the effects of a synthetic SF-1 stimulator (4-(heptyloxy)phenol - HxP; 1×10(-7)M) and a synthetic SF-1 inhibitor (F0160; 1×10(-5)M) on the secretion of estradiol and oxytocin (OT) from granulosa cells (from follicles>1cm) and the secretion of progesterone (P4) and OT from luteal cells (days 11-16 of the estrous cycle) were investigated. The levels of SF-1 mRNA and protein were higher in granulosa cells (P<0.05) from follicles>1cm than in cells from follicles<1cm. In luteal tissue, the mRNA abundance was the highest (P<0.05) on days 6-10 of the estrous cycle, and the amount of protein was the highest on days 6-15 (P<0.05). The lowest levels of mRNA and protein for SF-1 were observed on days 16-19 of the estrous cycle (P<0.05). The abundance of SF-1 mRNA decreased at 9-12 weeks of pregnancy (P<0.05). The stimulation of the studied cells with HxP increased P4 and estradiol secretion from luteal and granulosa cells, respectively, and OT secretion from both types of cells. The SF-1 inhibitor did not affect hormone secretion by either type of cell, but it did diminish the effect induced by the SF-1 stimulator. The obtained data revealed estrous cycle-dependent levels of mRNA and protein for SF-1 in luteal tissue, and the use of a specific SF-1 stimulator and a specific SF-1 inhibitor confirmed the involvement of this receptor in steroidogenesis and OT secretion from cultured granulosa and luteal cells. These findings suggest that the SF-1 receptor participates in the local regulation of ovarian function during both the estrous cycle and the first trimester of pregnancy in cows. Furthermore, the concentrations of the SF-1 inhibitor and stimulator that we used in the primary cell culture could effectively modify the activity of this receptor.