ABSTRACT

The aim of this study was to establish the gestational- and labour-associated variation in the relative abundance of prostaglandin synthase-1 (PGHS-1) and prostaglandin synthase-2 (PGHS-2) mRNA in ovine placenta (cotyledons). Cotyledons were collected from non-labouring ewes at 40–145 days of gestation (n=25) and from ewes in active labour (145–147 days, n=5). The relative abundance of PGHS-1 and PGHS-2 mRNA transcripts was determined by Northern blot analysis and laser densitometry, using a 2·3 kb sheep and a 1·2kb mouse cDNA probe respectively. Data were expressed as a ratio of PGHS transcript hybridization/18S rRNA hybridization. During pregnancy, the relative abundance of PGHS-2 mRNA increased sevenfold, from 0·19±0·04 at 40–85 days (n=5) to 1·39±0·05 at 140–145 days (n=4) (P<0·01). PGHS-1 mRNA relative abundance did not change significantly (P>0·05) during gestation. Neither PGHS-1 nor PGHS-2 mRNA relative abundance changed significantly in association with labour onset at term (n=5) when compared with the relative abundance observed at 140–145 days (n=4) (P>0·05). The data obtained in this study are consistent with the hypothesis that PGHS-1 is constitutively expressed in ovine placenta during pregnancy and at the time of labour, and that PGHS-2 is induced during the second half of pregnancy. It remains to be established to what extent these two isozymes contribute to the net prostaglandin-forming capacity of the ovine placenta, particularly at the time of labour.

Low birthweight is a risk factor for neonatal mortality and adverse metabolic health, both of which are associated with inadequate prenatal adipose tissue development. In the present study, we investigated the impact of maternal undernutrition on the expression of genes that regulate fetal perirenal adipose tissue (PAT) development and function at gestation days 89 and 130 (term=145 days). Singleton fetuses were taken from adolescent ewes that were either fed control (C) intake to maintain adiposity throughout pregnancy or were undernourished (UN) to maintain conception weight but deplete maternal reserves (n=7/group). Fetal weight was independent of maternal intake at day 89, but by day 130, fetuses from UN dams were 17% lighter and had lower PAT mass that contained fewer unilocular adipocytes. Relative PAT expression of IGF1, IGF2, IGF2R and peroxisome proliferator-activated receptor gamma (PPARG) mRNA was lower in UN than in controls, predominantly at day 89. Independent of maternal nutrition, PAT gene expression of PPARG, glycerol-3-phosphate dehydrogenase, hormone sensitive lipase, leptin, uncoupling protein 1 and prolactin receptor increased, whereas IGF1, IGF2, IGF1R and IGF2R decreased between days 89 and 130. Fatty acid synthase and lipoprotein lipase (LPL) mRNAs were not influenced by nutrition or stage of pregnancy. Females had greater LPL and leptin mRNA than males, and LPL, leptin and PPARG mRNAs were decreased in UN at day 89 in females only. PAT gene expression correlations with PAT mass were stronger at day 89 than they were at day 130. These data suggest that the key genes that regulate adipose tissue development and function are active beginning in mid-gestation, at which point they are sensitive to maternal undernutrition: this leads to reduced fetal adiposity by late pregnancy.