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Effect of late gestational nutrient restriction on gene expression of markers of white and brown adipocytes in the postnatal sheep

Presented at the Neonatal Society 2009 Summer Meeting (programme).

Modi N1, Thomas EL2, Uthaya S1, Bell JD2

1 Section of Neonatal Medicine, Division of Medicine, Chelsea & Westminster Hospital campus, Imperial College London, London, SW10 9NH, UK
2 Medical Research Council Clinical Sciences Centre, Hammersmith Hospital campus, Imperial College London, London, W12 0NN, UK

Background: The classical approach to the study of the body composition of the newborn infant is to express this as chemical composition, or in its simplest form as fat and fat-free mass, where fat is ether-extractable fat and fat-free mass is the remainder and includes the stroma of adipose tissue. The recognition of adipose tissue (AT) as a metabolically active endocrine organ suggests that a distinction into adipose and non-adipose (lean) compartments may be biologically more meaningful.

Aim: To describe the body composition of the healthy term/near term newborn infant.

Methods: We extracted details of term/near term infants from our database of anthropometry and whole body AT magnetic resonance images complied from a series of research ethics approved investigations in healthy infants. Imaging is carried out in natural sleep as previously described by our group (1). Image analysis to quantify AT depots was conducted blind to identity; the compartments Internal Abdominal, Internal Non- Abdominal, Deep Subcutaneous Abdominal, Deep Subcutaneous Non-Abdominal, Superficial Subcutaneous Abdominal and Superficial Subcutaneous Non Abdominal are quantified individually and summated to derive Total AT volume (2). AT volume is converted to mass (ATM) based on AT density of 0.9g/cc. Non Adipose Tissue (lean) content is derived as the difference between body weight and ATM. We compared anthropometry and body composition in boys and girls with adjustment for postmenstrual age at time of imaging. Data analysis was conducted using SPSS version 16. Values are mean (SD) unless otherwise stated.

Results: We present data from 140 infants (73 boys, 67 girls) born at a gestational age of 39.6 (1.5) weeks and imaged at 6.6 (5.8) days (table).

Table: Comparison of anthropometry and body composition; all parameters evaluated at a postmenstrual age of
40.6 weeks; values are mean (se)

Though girls were significantly lighter, shorter and had smaller head circumferences than boys there was no significant difference in AT content. Girls do however have a highly significant decrease in non-adipose tissue (lean) mass. There were no significant differences in any of the 6 individual adipose tissue depots.

Conclusions and Discussion: In this large study in a heterogeneous group of healthy newborn infants, we provide novel data on body composition. We show a greater non-adipose content in boys and no major differences between the sexes in AT partitioning. Humans are unique among mammalian species in possessing substantial AT stores at birth, with specific compartments serving distinct metabolic and endocrine functions. We speculate that the greater biological resilience of the female in comparison with the male neonate may at least in part be a consequence of the survival advantage conferred by a more favourable adipose to non-adipose body composition.

1. Harrington et al. Lipids 2002; 37(1):95-100
2. Modi et al. Pediatr Res 2009; 65(5):584-587

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