Operational Lumped Constant for FDG in Normal Adult Male Rats

We determined an operational value for the lumped constant to be used in measurements of the local rate of cerebral glucose use (lCMRglc) with FDG in normal adult male rats. Methods: The standard quantitative autoradiographic method was used with 2-deoxy-D-14C-glucose (14C-DG) and with 14C-FDG in awake normal adult male rats. Timed arterial blood samples were drawn for 45 min after the bolus and assayed for plasma glucose and 14C concentrations. At the end of the 45-min exper-imental period, the rats were killed, and their brains were re-moved and divided in half sagittally. One hemisphere was immediately frozen and assayed for local 14C concentrations by quantitative autoradiography; the other was weighed, ho-mogenized in t-octylphenoxypolyethoxyethanol solution, and assayed for 14C concentrations in the whole brain by liquid scin-tillation counting. Paired rats (3 pairs), one in each pair receivin