Presented at the Neonatal Society 2004 Spring Meeting.
Gnanalingham MG1, Mostyn A1, Symonds ME1, Giussani DA2, Stephenson T1, Gardner DS1
1 Centre for Reproduction and Early Life, Institute of Clinical Research, University of Nottingham
2 Department of Physiology, University of Cambridge.
Introduction: Chronic compression of the umbilical cord in fetal sheep sufficient to restrict fetal blood supply by 30% mimics the degree of cord compression noted in about 40% of human pregnancies, and results in a range of fetal endocrine adaptations, including increased fetal plasma cortisol (1). Uncoupling protein-1 (UCP1) is a member of the inner mitochondrial protein superfamily, specific to brown adipose tissue (BAT) and is primarily involved in thermogenesis by uncoupling ATP synthesis. The effect of chronic umbilical cord compression (UC) on the abundance of UCP1 mRNA, protein and guanosine diphosphate (GDP) binding (estimate of the potential thermogenic activity of the tissue) was determined.
Methods: Nine ewes were entered into the study, which were all chronically instrumented with fetal vascular catheters at 118 ± 2 days (term @147 days). Five fetuses were then subjected to 3 days UC beginning at 125 days gestation by automated compression of the umbilical cord, with the remaining 4 acting as controls (C). At 137 ± 2 days gestation, all fetuses were humanely euthanased (100 mg kg-1 pentobarbital sodium: Euthatal, i.v.), BAT dissected and frozen in liquid nitrogen. All procedures were carried out according to U.K. animal legislation. UCP1 mRNA abundance was determined by RT-PCR using oligonucleotide primers designed specifically to ovine UCP1, mitochondrial UCP1 protein abundance was measured by immunoblotting and GDP binding was determined by non-competitive radioactive assay. The mRNA data is represented as means and S.E.M. in arbitrary units, as a ratio of 18S rRNA and expressed as a percentage of a reference sample; the mitochondrial protein data as a percentage of a reference sample and the GDP binding as pMol. mg protein-1. Statistical differences between groups were analysed by an unpaired (p<0.05) Mann-Whitney U test and correlations by Spearman’s Rank Order Test.
Results: There were no significant differences in body or BAT weights between groups. UC resulted in enhanced abundance of UCP1 mRNA (C 70.0 ± 2.4; UO 121.8 ± 4.2, p<0.05), UCP1 protein (C 57.4 ± 1.3; UO 108.5 ± 4.7, p<0.05) and GDP binding (C 19.3 ± 1.3; UO 36.3 ± 2.8, p<0.05) in BAT. Overall, GDP binding was positively correlated with UCP1 mRNA (R2 = 0.73, p<0.05) and UCP1 protein (R2 = 0.78, p<0.01).
Conclusions: Chronic UC results in precocious maturation of brown adipose tissue. The improved thermogeneic capacity of BAT may subsequently act to prevent the growth-restricted fetus from hypothermia at birth following cold exposure to the extrauterine environment.
References
1. Gardner DS, Fletcher AJW, Fowden AL, Giussani DA. Endocrinology 2001, 142: 589-598.