Effect of labor on glucocorticoid receptor (GR(Total), GRalpha, and GRbeta) proteins in ovine intrauterine tissues.

Objective: Activation of the fetal hypothalamic-pituitary-adrenal axis and a concurrent increase in plasma cortisol concentration plays a crucial role in parturition in sheep. The effects of cortisol on intrauterine tissues are mediated, in part, by glucocorticoid receptors (GR). In the present study, we determined the temporal and tissue-specific expression of GR(Total), GRalpha, and GRbeta isoforms in ovine placenta, fetal membranes, and uterus during the onset and progression of labor.

Ontogeny and regulation of ovine placental prostaglandin E2 synthase.

Recent evidence suggests that ovine placental output of prostaglandin (PG) E2 rises through late gestation partly because of a direct effect of cortisol on PGH2 synthase 2 (PGHS-2) expression and activity within trophoblast tissue. Synthesis of PGE2 is also dependent, however, on PGE2 synthase (PGES), which converts PGH2 to PGE2. We hypothesized that PGES is expressed in the ovine placenta, and that, similar to PGHS-2, expression increases through gestation and is regulated positively by cortisol.

Glucocorticoid regulation of human and ovine parturition: the relationship between fetal hypothalamic-pituitary-adrenal axis activation and intrauterine prostaglandin production.

Birth in many animal species and in humans is associated with activation of hypothalamic-pituitary-adrenal function in the fetus and the increased influence of glucocorticoids on trophoblast cells of the placenta and fetal membranes. We suggest that in ovine pregnancy glucocorticoids directly increase fetal placental prostaglandin production, and indirectly increase prostaglandin production by maternal uterine tissues through the stimulation of placental estradiol synthesis. The events of ovine parturition are compared with those of human parturition.

Effects of labor on pituitary expression of proopiomelanocortin, prohormone convertase (PC)-1, PC-2, and glucocorticoid receptor mRNA in fetal sheep.

We hypothesized that the concurrent prepartum rise in adrenocorticotropic hormone (ACTH) and cortisol in the plasma of fetal sheep might be attributable to altered expression of pituitary endoproteases, prohormone convertase (PC)-1, and PC-2, or to changes in pituitary expression of glucocorticoid receptor (GR) that would influence negative feedback potential. We obtained pituitary tissue from fetal sheep during late pregnancy (d 100-d 145, term) and at precise times during the process of labor and used in situ hybridization to localize and quantify mRNA levels. Proopiomelanocortin (POMC) mRNA was regionally distributed (pars intermedia > inferior pars distalis > superior pars distalis) and increased within the pars distalis during late pregnancy and with labor.

Temporal expression of prostaglandin H synthase type 2 (PGHS-2) and P450(C17)in ovine placentomes with the natural onset of labour.

Labour in the sheep is preceded by increased tissue and plasma prostaglandin (PG) concentrations, and PGs could potentially contribute to the regulation of P450(C17)in placental tissue. Therefore, we determined the cellular localization and temporal pattern of expression of P450(C17)and prostaglandin H synthase type 2 (PGHS-2), the primary PG synthetic enzyme, in intrauterine tissues from three groups of pregnant ewes at term; animals not in labour (NIL;n=5; 140-145 days of gestation), animals in early labour (EL;n=6; 143-149 days) and animals in active labour (L;n=6; 145-149 days). Allocation of animals into the three groups was based on continuous monitoring and assessment of myometrial contractile activity (EMG) and changes in the intrauterine pressure (IUP).