Molecular regulation of progesterone synthesis in the bovine corpus luteum

Abstract

In bovine luteal cells, progesterone can directly affect its own synthesis by increasing the activity of 3β-HSD. The effect of progesterone on its own secretion coincides with increased expression of the genes for 3β-HSD, StAR, and cytochrome P450scc. Therefore, progesterone regulates its own synthesis by affecting the activity of the enzymes that take part in luteal steroidogenesis, and also by affecting the expression of the genes for these enzymes. The aims of this study were: (a) to determine whether progesterone affects the expression of the gene for its own receptor, thereby affecting its own synthesis; and (b) to determine whether oxytocin and noradrenaline affect the expression of the genes for the oxytocin receptor (OT-R), the progesterone receptor (P4-R), and the β<sub>2</sub> receptor (β<sub>2</sub>-R), thereby regulating luteal steroidogenesis. Two populations of luteal cells were used in the present study: from 6<sup>th</sup>–10<sup>th</sup> and 11<sup>th</sup>–16<sup>th</sup> days of the estrous cycle, which were isolated from <i>corpus luteum</i> (CL) from slaughtered cows. The luteal cells were treated for six hours with one of the following hormones: luteinizing hormone (LH; 100 ng/ml); progesterone (P<sub>4</sub>; 10<sup>–5</sup>M); progesterone antagonist (aP<sub>4</sub>; 10<sup>–5</sup>M); noradrenaline (NA; 10<sup>–5M</sup>); or actinomycin D (ActD; 500 ng/ml). After treatment, the medium was collected for the determination of progesterone concentration. With LH, the P<sub>4</sub> concentration in the medium increased with both 6<sup>th</sup>–10<sup><sup>th</sup> and 11<sup>th</sup>–16<sup>th</sup> days. None of the other treatments affected the progesterone concentration of the medium. The level of expression of the genes for OT-R, P<sub>4</sub>-R and β<sub>2</sub>-R were determined. Total RNA was extracted from cells, treated with DNase, and subjected to reverse transcription. Treatment with luteinizing hormone was the only treatment that increased the level of expression of the gene for P<sub>4</sub>-R in both 6<sup>th</sup>–10<sup>th</sup> and 11<sup>th</sup>–16<sup>th</sup> days of the estrous cycle. Both treatment with luteinizing hormone and treatment with progesterone increased the level of expression of the gene for OT-R in 6<sup>th</sup>–10<sup>th</sup> days. The basal level of expression of the gene for OT-R was higher in 6<sup>th</sup>–10<sup>th</sup> days than in 11<sup>th</sup>–16<sup>th</sup> days. This suggests that there is positive feedback between progesterone and oxytocin, with both playing a role as a local, intra-ovarian factor that enhances the function of the <i>corpus luteum</i>.

Lipopolysaccharide enhances apoptosis of corpus luteum in isolated perfused bovine ovaries in vitro

“…P 4 synthesis is the most important indicator of functional integrity of the CL (Rekawiecki et al 2008). In that regard, increased P 4 synthesis following LH treatment is evidence of CL responsiveness (Skarzynski et al 2008).…”

Involvement of the oestrogenic receptors in superior mesenteric ganglion on the ovarian steroidogenesis in rat

“…Also, taking into account that Kotwica et al (2004) and Rekawiecki et al (2008) have postulated the autoregulation of P 4 synthesis in the corpus luteum, which affects the transcription of the genes encoding steroidogenic enzymes, it can be assumed that the values of P 4 can be due to the increase in the activity and gene expression of 3b-HSD caused by the same P 4 released throughout time. The accumulation of P 4 in ovarian steroidogenic cells is also influenced by the participation of the enzyme 20a-HSD, a P 4 degradation enzyme, which has been determined, cloned and sequenced in the corpus luteum of rats (Mao et al 1997).…”

Use of the progesterone (P4) receptor antagonist aglepristone to characterize the role of P4 withdrawal for parturition and placental release in cows

“…Thus, luteolysis was clearly induced by antiprogestin treatment, an observation also made in the dog (Kowalewski et al 2009). Luteolysis may result from a direct effect on luteal PGRs (Rekawiecki et al 2008) or an indirect one by stimulating the synthesis of luteolytic prostaglandins. To allow for this effect of an antiprogestin treatment, the endocrine environment of late gestation seems to be a prerequisite, as Ap when administered to early pregnant cows using the same dosages led to a significant increase in P 4 levels during the observational period of 7 days after the start of treatment (Breukelman et al 2005).…”