Technical Note: In vivo estimation of lipogenesis using a bolus injection of [U-13C]glucose in pigs

The use of radioactive isotopes to measure de novo lipogenesis in pigs has been well established. Different from radioactive isotopes, stable isotopes present little or no risk to human and animal subjects. Therefore, the objective of this study was to adapt the method of bolus injection of radioactive glucose (14C) to use 13C-labeled glucose to estimate de novo lipogenesis in finishing pigs. Five vein-catheterized gilts received 3.0 kg/d of a commercial diet for 2 wk. On the last day, the pigs received a bolus injection of [U-13C]glucose (12 mg/kg body weight). A serial of blood samples was taken for 4 h to determine the glucose rate of disappearance (Rd) from plasma glucose isotopic enrichment (IE). The 13C IE of lipids was determined from adipose tissue biopsies collected at 1, 2, and 3 h after the bolus injection and from adipose tissue collected after pig euthanasia 4 h after the bolus. Lipogenesis was estimated from the incorporation of 13C from glucose into adipose tissue lipids. Glucose Rd, estimated using a double-exponential function, averaged 5.4 ± 1.4 mmol/min. The IE of lipids increased linearly during the 4 h following the bolus injection (P < 0.05). The rate of incorporation of glucose into lipids, estimating lipogenesis, averaged 9.0 µg glucose/(min × g of lipids) 4 h after the bolus injection. In conclusion, the in vivo method using a bolus injection of [U-13C]glucose allows a successful estimation of de novo lipogenesis in finishing pigs.