title: The lumped constant in the deoxyglucose procedure declines with age in Fischer-344 rats.
abstract: Concentrations of [14C]2-deoxy-D-glucose ([14C]DG) and of glucose were measured in plasma of arterial and sagittal sinus venous blood from awake Fischer-344 rats at 3, 12, and 24 months of age, during continuous intravenous infusion of [14C]DG and after a steady-state arterial plasma concentration of [14C]DG was reached. Brain extraction, i.e., the difference between arterial and venous plasma concentrations divided by the arterial plasma concentration, was calculated for both [14C]DG and glucose. Because exchange of both substances between rat plasma and erythrocytes is slow, the ratio of the brain extraction of [14C]DG to that of glucose is identical to the lumped constant in the deoxyglucose procedure of Sokoloff et al. [J. Neurochem. 28, 897-916. (1977)]. This ratio equaled 0.502 +/- 0.015 (SEM) at 3 months, 0.456 +/- 0.007 at 12 months, and 0.418 +/- 0.006 at 24 months of age (n = 15); the means differed significantly from each other (p less than 0.05). The results indicate that the lumped constant declines between 3 and 24 months of age in awake rats, and suggest that many reported age reductions in regional cerebral glucose utilization, of 15-25%, are artifactual.
mesh_terms: D000375:Aging; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001921:Brain / Q000098:blood supply / Q000378:metabolism*; D002536:Cerebral Arteries; D003837:Deoxy Sugars / Q000097:blood*; D003847:Deoxyglucose / Q000097:blood* / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism; D006207:Half-Life; D007700:Kinetics; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D014680:Veins
chemical_list: D001786:Blood Glucose; D003837:Deoxy Sugars; D003847:Deoxyglucose