Lipid composition of brown adipose tissue as related to nutrition during the neonatal period in hypotrophic rats.

Animals with intrauterine growth retardation (IUGR) were obtained by artery clamping of one uterine horn of the rat on day 17 of gestation. Body weight reduction was at least 30% as compared with the control animals that originated from the other horn. Brown adipose tissue (ISBAT), which plays a role in nonshivering thermogenesis, was greatly reduced during the period studied (fetuses from the day before up to 10 days after birth). Total lipids were very low after birth and increased rapidly up to age 3 days. Nevertheless, lipids of IUGR rats were lower during 48 hours and became identical to the controls only at 3 days. This deficiency could play a role in the high mortality rate observed just after birth. The developmental pattern of fatty acid methyl esters of ISBAT studied by gas chromatography method was identical in both groups of animals. On the other hand, a change from mainly saturated to a greater proportion of unsaturated fatty acids occurred just after the first suckling. This switch was closely correlated to the fatty acid composition of the rat milk. Incorporation of 14C from [14C]glucose into lipids of ISBAT was lower in IUGR rats up to 48 hours as compared with control values and overlapped the control value after. This could explain the catching up in lipid content in IUGR at 3 days of life. Also it could be correlated with the hypoglycemia observed in the IUGR rats during the neonatal period.