EFFECTS OF ELEVATED PLASMA EPINEPHRINE ON GLUCOSE-UTILIZATION AND BLOOD-FLOW IN CONSCIOUS RAT-BRAIN

Acute glucoprivation increases cerebral blood flow (CBF), which is oft en attributed to the associated rise in plasma epinephrine levels. Thi s study examined directly the effects of comparable increases in plasm a epinephrine levels achieved by continuous intravenous infusions of e pinephrine in normoglycemic, unanesthetized rats on local and overall CBF and cerebral glucose utilization (lCMR(glc)). CBF was determined b y the autoradiographic [C-14]iodoantipyrine method in six unanesthetiz ed rats in which epinephrine dissolved in 1% ascorbic acid-1 mM EDTA w as infused at a rate of 1 mu g/min and in five normal controls infused with the vehicle alone. lCMR(glc) was determined by the autoradiograp hic [C-14]deoxyglucose method in six conscious rats infused similarly with the epinephrine solution and in six normal controls treated with the vehicle alone. The epinephrine infusions raised arterial plasma ep inephrine levels 10- to 20-fold and increased arterial blood pressure and plasma glucose levels. Local CBF, however, was significantly chang ed (P < 0.05, Student's t-test) in only 2 of 25 structures examined, a nd the changes were decreases not increases. lCMR(glc) was not changed significantly in any of 42 brain structures examined, and average blo od flow and glucose utilization in the brain as a whole were unaffecte d. These results show that high circulating levels of epinephrine simi lar to those accompanying glucoprivation alter neither local nor overa ll CBF and glucose utilization and cannot explain the increases in CBF associated with glucoprivation.