Presented at the Neonatal Society 2008 Spring Meeting.
Yiallourides M1, Sebert S1, Rhind SM2, Rae MT2, Stephenson T1, Symonds ME1, Budge H1
1 Centre for Reproduction and Early Life, Institute of Clinical Research, University Hospital, Nottingham NG7 2UH, UK
2 Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
Background: Maternal nutrient restriction during early to mid-gestation reduces placental mass in conjunction with increased glucocorticoid receptor (GR) mRNA expression, decreased 11 β-hydroxysteroid dehydrogenase type 2 (11βHSD2) mRNA expression and loss of cell proliferation (1).
Aim: The aim of this study was to determine whether the timing of maternal nutrient restriction determines placental responsiveness to glucocorticoids and has concomitant effects on cell proliferation.
Study design: Placentae were sampled from singleton bearing pregnant sheep at 110 days gestation (term 145 days). At conception, they were randomly allocated to control feeding i.e. 100% of total metabolisable energy requirements or one of four nutrient restricted (NR) groups that were fed half this amount from either 0 to 30, 31 to 65, 66 to 110 or 0 to 110 days gestation. All were euthanased by barbiturate overdose at 110 days gestation. Individual placentomes were dissected and either placed into 10% formalin and embedded in paraffin wax for histological analysis or stored at -80ºC for molecular analyses. All procedures had the required Home Office approval and were performed under UK legislation.
Methods: Cell proliferation was determined by proliferating cell nuclear antigen (PCNA) expression. Placentome sections (5μm), were stained by PCNA-specific antibody using the BOND-maX system. Image analysis and quantification was carried out using Volocity Acquisition and Quantification software for ten fields from each section. An index of cell proliferation (PCNA index) was assessed as a percentage of positively stained cells per total number of cells per field. GR and 11βHSD2 mRNA expression were estimated by real time PCR normalised to 18s rRNA. Results were analysed by two-way ANOVA followed by Fisher’s Least Significance method, using SPSS version 15.0.
Results: There were no differences in fetal or placental weights between the control and NR groups. The abundance of GR was increased in those animals NR between 65-110 days gestation (P<0.05), while the index of cell proliferation in this group was decreased (P<0.05). There was no effect of maternal food intake on the mRNA abundance of 11βHSD2.
Conclusion: Maternal nutrient restriction, commencing at 65 days gestation coincident with the period immediately after maximum placental growth, specifically increased glucocorticoid sensitivity in the placenta. This response may be mediated by the decline in maternal plasma cortisol that occurs with reduced food intake during early pregnancy (2). Interestingly, despite a reduction in cell proliferation within the placenta at this stage, there was no immediate effect on placental mass. These adaptations may result in a resetting of the fetal endocrine environment, thereby increasing risk of cardiovascular or metabolic compromise in later life (3).
References
1. Gnanalingham MG et al. Reproduction 2007; 134: 615-623
2. Bispham J et al. Endocrinology 2003; 144: 3575-3585
3. Symonds ME et al. Reproduction, Fertility and Development 2007; 19: 53-63