The differential production of prostaglandin (PG) F(2 alpha) and PGE(2) within the uterine compartment may play a role in controlling myometrial contraction. We hypothesized that the enzymes downstream of PG endoperoxide synthase-2 (PGHS-2) determine the ratio of PGF(2 alpha) and PGE(2) in the utero-ovarian vein plasma and the time of normal and preterm labour onset. The aim of this study was to simultaneously determine the expression of PGF and PGE synthases (PGFS and PGES) in gestational tissues at spontaneous and induced-preterm labour in sheep. Myometrial, endometrial and placental tissue were obtained from ewes in dexamethasone-induced preterm labour, age-matched control ewes, and ewes in spontaneous term labour for analysis of mRNA expression by real-time PCR. PGFS mRNA expression was significantly increased following dexamethasone-induced and spontaneous labour onset in placentome (P<0.01) but was unchanged in the myometrium and endometrium. In contrast, PGES mRNA expression remained unchanged or decreased. PGHS-2 mRNA expression was increased in all tissues examined in both dexamethasone-induced and spontaneous labour (P<0.001). Plasma PGE(2) and PGF(2 alpha) concentrations rose in both dexamethasone-induced and spontaneous labour with the ratio of PGF(2 alpha):PGE(2) increased with labour onset (P<0.05). These results are consistent with the hypothesis that the increased expression, of PGFS is responsible for the increased PGF(2 alpha):PGE(2) ratio and this, together with increased PGHS-2 expression, accounts for myometrial activity at labour onset. The findings point to PGFS expression as a key factor in regulating the uterotonic process in the sheep.
HK Palliser, GT Ooi, JJ Hirst, G Rice, NL Dellios, RM Escalona and IR Young
W J McLaren, I R Young, M H Wong and G E Rice
Parturition in the sheep is preceded by an increase in the synthesis of prostaglandins by intrauterine tissues. Prostaglandin G/H synthase (PGHS) is the central enzyme involved in prostanoid production. Its expression is enhanced during late gestation in the ewe. Recent studies have identified two PGHS isozymes, termed PGHS-1 and PGHS-2. The labour-associated expression of the two isozymes of PGHS in the sheep has not been characterized.
This study investigated the changes in expression of immunoreactive PGHS-1 and PGHS-2 in ovine amnion and placenta following glucocorticoid-induced labour. Ewes underwent surgery to implant fetal and maternal vascular cannulae and uterine electromyogram electrodes between 118 and 125 days of gestation. Fetal sheep were administered either the glucocorticoid betamethasone (n=5) or saline (control n=6) by direct transabdominal intrafetal injection. Ewes from the betamethasone-injected group were killed in the first stage of labour as indicated by uterine electromyographic activity. Ewes from the saline-injected group were killed at the same time to obtain age-matched control tissue. The time taken to euthanasia following induced-labour onset in the glucocorticoid-injected animals was 56·6 ± 0·8 h post-injection.
Plasma endocrine profiles in the maternal and fetal circulation following glucocorticoid injection were comparable to those observed following normal spontaneous delivery. At post-mortem, amnion and cotyledons were collected in liquid N2 and stored at −70 °C. Solubilized tissue extracts were prepared and analysed by Western blots using polyclonal antibodies to PGHS-1 and PGHS-2 isozymes. Fetal amnion contained PGHS-1 isozyme at day 133 of gestation, as demonstrated in the saline-injected animals. Slightly higher PGHS-1 immunoreactivity was observed following induced-labour onset, although this did not reach statistical significance (P>0·05). PGHS-2 enzyme was not detectable in amnion. PGHS-2 expression was also not induced following labour onset.
In contrast, PGHS-2 demonstrated enhanced expression following glucocorticoid-induced labour in ovine cotyledon. This tissue contained PGHS-1 enzyme, but immunoreactive levels were minimal and demonstrated limited regulation at labour.
These data suggest that the previously reported rise in placental PG production at term in the sheep is predominantly due to increased expression of the PGHS-2 isozyme. This suggests that PGHS-2 contributes to PG production at term labour in sheep or is induced by the mechanisms controlling ovine parturition. PGHS-1 isozyme is produced constitutively in ovine amnion and may contribute to the gestational increase in PG formation by intrauterine tissues.
Journal of Endocrinology (1996) 151, 125–135
N E Curtis, P W M Ho, R G King, W Farrugia, E K Moses, M T Gillespie, J M Moseley, G E Rice and M E Wlodek
Parathyroid hormone-related protein (PTHrP) gene expression and/or immunoreactive protein have previously been identified in the uterus and intrauterine gestational tissues. The putative roles of PTHrP during pregnancy include vasodilatation, regulation of placental calcium transfer, uterine smooth muscle relaxation and normal fetal development. The aims of this study were 1) to determine the tissue-specific and temporal expression of PTHrP mRNA and immunoreactive protein in human gestational tissues collected at preterm and term; and 2) to determine the effect of labour on PTHrP expression by collecting these tissues from women undergoing elective caesarean section (before labour), intra-partum caesarean section during spontaneous-onset labour (during labour), and women with spontaneous labour and normal vaginal delivery (after labour). Total RNA and protein were extracted from placenta, amnion (over placenta and reflected) and choriodecidua for analysis by Northern blot (using a specific human PTHrP cDNA probe), and by N-terminal PTHrP RIA respectively. In amnion over placenta, reflected amnion and choriodecidua both PTHrP mRNA relative abundance and immunoreactive protein were significantly elevated at term compared with preterm (P<0·01). At term, both PTHrP and its mRNA were significantly greater in amnion than in placenta and choriodecidua (P<0·05). Also, both PTHrP and its mRNA were significantly elevated in amnion over placenta compared with reflected amnion (P<0·05). The expression of PTHrP and its mRNA did not change in association with term labour or rupture of the fetal membranes, therefore this study provides no evidence for a specific PTHrP role in the onset and/or maintenance of term labour. However, the significant up-regulation of PTHrP mRNA and protein in the fetal membranes at term compared with preterm suggests an important role in late human pregnancy.
Journal of Endocrinology (1997) 154, 103–112