Sources of blood glycerol during fasting.
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.
Jensen
M D
MD
Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota 55905, USA.
Chandramouli
V
V
Schumann
W C
WC
Ekberg
K
K
Previs
S F
SF
Gupta
S
S
Landau
B R
BR
D000328:Adult; D001834:Body Water / Q000378:metabolism; D002250:Carbon Radioisotopes; D003903:Deuterium; D005215:Fasting; D005990:Glycerol / Q000097:blood*; D006801:Humans; D007700:Kinetics; D008079:Lipoproteins, VLDL / Q000097:blood; D008297:Male; D014280:Triglycerides / Q000097:blood; D014867:Water
D002250:Carbon Radioisotopes; D008079:Lipoproteins, VLDL; D014280:Triglycerides; D014867:Water; D003903:Deuterium; D005990:Glycerol