Involvement of Progesterone, Oxytocin, and Noradrenaline in the Molecular Regulation of Steroidogenesis in the Corpus Luteum of the Cow

The aim of this study was to determine: (a) whether progesterone affects the expression of the gene for its own receptor, thereby affecting its own synthesis; (b) whether oxytocin (OT) and noradrenaline (NA) influence the expression of gene for receptor (R) of OT (OT-R), progesterone (PR-R), and β2-R, determined by means of real-time PCR; (c) whether OT, progesterone, and NA affects the protein level for receptors of OT and β2, determined by means of the Western blot. Luteal cells isolated from the corpus luteum (CL) on days 6-10 and 11-16 of the oestrous cycle were used in the study. The luteal cells were treated with luteinising hormone (LH; 100 ng/mL), progesterone (10 M), OT (10 M), NA (10 M), and prostaglandin (PG) E2 (10 M) for 6 h for the gene expression and for 24 h for the measurement of receptor protein. Thereafter, medium was collected for the determination of progesterone concentration. LH and PGE2 increased luteal secretion of P4 on days 6-10 and 11–16 after 6 h and 24 h stimulation. LH increased expression of the gene for PR-R on days 6-10 and 11-16 but PGE2 only on days 6-10 of the oestrous cycle. OT stimulated gene expression for its own receptor on days 11-16, while progesterone only increased OT-R protein on days 6-10 of the cycle. The obtained data suggest a positive intra-ovarian feedback mechanism between progesterone and OT that enhances the function of CL in the cow.