Epidemiological studies have shown that infants of low birth weight show poor neonatal growth and increased susceptibility to adult diseases such as diabetes in later life. Pigs provide an ideal model to examine the influence of size at birth due to the natural variance in piglet weight within a litter. This study examined whether birth weight influences the expression of UCP3 in fat and muscle and its endocrine regulation in neonatal pigs.
Piglets from 11 litters were ranked according to body weight at birth and 3 animals from each were assigned to small (SFD n = 11), normal (NFD n = 11) or large for dates (LFD n = 11) groups. Body weight was recorded on days 7 and 14 of postnatal life when a venous blood sample was also taken. Piglets were humanely euthanased with an overdose of barbiturate (100 mg kg-1 pentobarbital sodium: Euthatal) on days 7 (n = 15) and 14 (n = 18) to obtain AT and SM. Plasma leptin, insulin like growth factor (IGF)-1 and insulin were measured using radioimmuno and enzymatic assays. UCP3 expression in AT and muscle was measured using RT-PCR as described previously (Mostyn et al. 2002). GLM and Spearman analysis were carried out to investigate statistical differences; results are presented as means ± standard errors.
The SFD group weighed less than the LFD group throughout the study. In AT, UCP3 expression on day 7 was found to be significantly lower in the SFD group (SFD, 34.4 ± 10.9; NFD, 69.48 ± 12.8; LFD 77.64 ± 9.0 % of reference (P < 0.05)) a similar trend was observed, but did not reach significance, on day 14 (Mostyn et al. 2003). UCP3 expression in SM was significantly higher than that of AT, but was similar between groups on both days. Leptin and insulin were significantly higher in the SFD group on day 7 only. IGF-1 was significantly higher in the LFD group on day 14.
In conclusion, low birth weight is associated with reduced expression of UCP3 in subcutaneous AT but not SM. UCP3 expression is differentially regulated by IGF-1, leptin and insulin (tradional regulators of body weight) and also size at birth. It remains to be established if these differences represent a ‘global’ effect on adipose tissue transcript expression or perpetuate into later life.