Free Fatty Acid and Glycerol Metabolism in Cold Exposed New-Born Rabbit

Abstract

The objectives of the present investigations were to determine the metabolic pathways and tracer kinetic patterns of circulating free fatty acid and free glycerol and determine the quantitative contribution to the calorigenesis in the main heat producing organs and tissues of the newly born. After i.v. injection of ¹⁴C-1-palmitate or ¹⁴C-1,3-glycerol (each 20 × 10⁶ dpm/100 g bwt) the turnover rate of plasma FFA and free glycerol was found 10.2 and 0.85 μMol/min/100 g bwt respectively in a thermoneutral environment of 35°C (Ta 35°C). Exposure to cold (Ta 20°C) caused a decrease in FFA turnover (5.84 μMol/min/100 g bwt) and an increase in free glycerol turnover (2.45 μMol/min/100 g bwt). The plasma concentrations of both metabolites increased significantly during cold exposure (FFA from 0.403 ± 0.041 to 0.518 ± 0.057; free glycerol from 0.251 ± 0.021 to 0.505 ± 0.057 μMol/ml plasma, respectively). These findings indicate that during cold induced calorigenesis in the new-born rabbit a substantial part of stored fatty acids are oxidized in brown adipose tissue itself, while the bulk of concomitantly produced glycerol is being released into the circulation, resulting in a ratio of FFA:glycerol turnover of 2.4:1. It practically means that in the cold during hydrolysis of triglycerides in adipose tissue instead of 3 only 2.4 moles of FFA entered and left the blood for each mole of glycerol.