Sources of blood glycerol during fasting

This is the authors' abstract. We don't add key points for this paper.

To determine the source(s) of blood and very low density lipoprotein (VLDL)-triglyceride glycerol during fasting, four men ingested (2)H(2)O from 14 to 20 h into a 60-h fast to achieve ~0.5% body water enrichment. At 60 h of fasting, glycerol flux was measured using [2-(14)C]glycerol. Blood was taken for measurement of (2)H enrichment at carbon 6 of glucose and at carbon 3 of free glycerol and VLDL-triglyceride glycerol. (2)H enrichment of the 2 hydrogens bound to carbon 3 of VLDL-triglyceride glycerol was 105 +/- 2% of the (2)H enrichment of the 2 hydrogens bound to carbon 6 of glucose, indicating isotopic equilibrium between hepatic glyceraldehyde 3-P and glycerol 3-P. The (2)H enrichment of the 2 hydrogens bound to carbon 3 of free glycerol was 17 +/- 3% of VLDL-triglyceride glycerol, indicating that a significant percentage of free glycerol in blood originated from the hydrolysis of circulating VLDL-triglyceride or a pool of glycerol with similar (2)H enrichment. Glycerol flux was 6.3 +/- 1.1 micromol. kg(-1). min(-1). Glycerol appearing from nonadipose tissue sources was then approximately 1.1 micromol. kg(-1). min(-1). Seven other subjects were fasted for 12, 42, and 60 h. A small percentage of glycerol in the circulation after 12 h of fasting was enriched with (2)H. The enrichment of the 2 hydrogens bound to carbon 3 of free glycerol in the longer periods of fasting was approximately 16% of the enrichment of the 2 hydrogens bound to carbon 6 of glucose. Therefore, as much as 15-20% of systemic glycerol turnover during fasting is not from lipolysis of adipose tissue triglyceride.