Luteal expression of steroidogenic factor-1 mRNA during the estrous cycle and in response to luteotropic and luteolytic stimuli in ewes.

Steroidogenic factor-1 (SF-1) is a transcription factor involved in regulating basal and/or cAMP-induced increases in expression of several components of the steroidogenic pathway, including cytochrome P450 side-chain cleavage (P450scc), steroidogenic acute regulatory protein (StAR), and 3β-hydroxysteroid dehydrogenase/Δ5, Δ4 isomerase (3β-HSD). In experiment 1, on days 3, 6, 9, 12, and 15 of the estrous cycle, steady-state concentrations (fmol/µg poly A+ RNA) of SF-1 mRNA in luteal tissue were 0.09±0.01, 0.17±0.01, 0.24±0.03, 0.30±0.09, and 0.20±0.05, respectively (estrus = day 0; n=4/d). Concentrations of SF-1 mRNA increased (p<0.05) between days 3 and 12, but were not different among the other days of the estrous cycle. Luteal concentrations of SF-1 mRNA and concentrations of progesterone in sera were highly correlated (p<0.01; r=0.72). In experiment 2, ewes on days 11 or 12 of the estrous cycle were injected with 25 mg prostaglandin F2α (PGF2α)into the jugular vein followed by an injection of 10 mg PGF2α im 2 h later. Corpora lutea were collected 4, 12, and 24 h after the first injection of PGF2α (n=4–5 ewes/time). Control luteal tissue was collected from ewes on days 11–13 of the estrous cycle, which had not been injected (n=4) or had been injected with saline 24 h previously (n=4). Steady-state concentrations of SF-1 mRNA had decreased (p<0.05) to 48% of control values by 4 h after injection, and remained low at 12 and 24 h. In experiment 3, ewes on days 9–12 of the estrous cycle were administered PGF2α (1 µmol), phorbol 12-myristate 13-acetate (PMA; 2 µmol), luteinizing hormone (LH; 20 µg), forskolin (50 µg), or vehicle (1 mL saline) directly into the ovarian artery. Corpora lutea were collected 0 (noninfused) 4, 12, or 24 h later (n=3–4 animals/treatment/time) for quantification of SF-1 mRNA. Steady-state concentrations of mRNA encoding SF-1 were not affected by infusion of PGF2α or PMA, although concentrations of mRNA encoding StAR and 3β-HSD were decreased (p<0.05) by these treatments. Concentrations of mRNA encoding SF-1 were increased (p<0.05) to 157 and 149% of control values by LH and forskolin, respectively, 12 h following infusion and returned to control values by 24 h following either treatment. In contrast, infusion of LH or forskolin did not change concentrations of mRNA encoding StAR, P450scc, or 3β-HSD. In summary, during the estrous cycle, the pattern of expression of SF-1 mRNA was similar to the pattern of concentrations of progesterone in serum and expression of mRNA encoding P450scc, but differed from that previously shown for 3β-HSD and StAR mRNA. The effects of administration of PGF2α on concentrations of SF-1 mRNA appeared to be dose-dependent. However, acute effects of PGF2α on mRNA encoding 3β-HSD and StAR were observed when concentrations of mRNA encoding SF-1 were not influenced. In addition, although LH or forskolin increased luteal SF-1 mRNA 12 h following infusion, no increases in mRNA encoding StAR, P450scc, or 3β-HSD were observed. Thus, during the midluteal phase of the estrous cycle, neither luteotropic nor luteolytic hormones appear to coordinately regulate mRNA encoding SF-1 and mRNA encoding StAR, P450scc, or 3β-HSD.