IGF-II and I are key components of postnatal growth and are involved in the proliferation of adipocytes. Cold exposure by winter shearing has been shown to promote growth and development and is dependant upon maternal nutrition. However, the effects on adipose IGF-I and II mRNA have not yet been determined.
Thirty-three multiparous ewes of similar body weight were entered into the study, fifteen were shorn (S) during mid gestation and eighteen left unshorn (US). Groups were further subdivided into nutrient restricted (NR; fed 50% of total energy requirements) over the final month of gestation and controls (C) were fed to 100% of requirements until term resulting in 4 groups SC (n=7), SNR (n=8), USC (n=9) and USNR (n=9). All lambs were born spontaneously and humanely euthanased (100mg kg -1 pentobarbital sodium: Euthatal, i.v) at day one of age. Perirenal brown adipose tissue (BAT) samples were weighed and stored at -80 oC until molecular analysis. The relative abundance of IGF-1 and IGF-2 mRNA were determined using RT-PCR as previously described (Bispham et al 2003), and results are expressed as means plus/minus standard error of mean shown in brackets.
Maternal cold exposure resulted in significantly heavier lamb total body weight in SC compared to the USC group (USC 4.6 (0.3); SC 5.5 (0.3) kg P<0.05) but no significant change in lamb adipose tissue weight. IGF-I mRNA was significantly increased in offspring from cold exposed ewes (USC 6 (2); SC 8.4 (2) P<0.05), with nutrient restriction exacerbating this effect (SNR 13.9 (3) P<0.05). However, cold exposure resulted in downregulation of IGF-II mRNA abundance (USC 3.7 (1); SC 2 (5); P<0.01).
In conclusion, cold exposure promotes fetal growth and postnatal BAT IGF-I expression whilst compromising IGF-II with little effect on fat mass. Such disturbances in the somatotrophic axis may have negative effects on downstream adipose tissue development and metabolism.
01 - 03 Nov 2004
Society for Endocrinology