Effects of elevated plasma epinephrine on glucose utilization and blood flow in conscious rat brain

Acute glucoprivation increases cerebral blood flow (CBF), which is often attributed to the associated rise in plasma epinephrine levels. This study examined directly the effects of comparable increases in plasma epinephrine levels achieved by continuous intravenous infusions of epinephrine in normoglycemic, unanesthetized rats on local and overall CBF and cerebral glucose utilization (1CMRglc). CBF was determined by the autoradiographic [14C]iodoantipyrine method in six unanesthetized rats in which epinephrine dissolved in 1% ascorbic acid-1 mM EDTA was infused at a rate of 1 microg/min and in five normal controls infused with the vehicle alone. 1CMRglc was determined by the autoradiographic [14C]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 epinephrine levels 10- to 20-fold and increased arterial blood pressure and plasma glucose levels. Local CBF, however, was significantly changed (P < 0.05, Student's t-test) in only 2 of 25 structures examined, and the changes were decreases not increases. 1CMRglc was not changed significantly in any of 42 brain structures examined, and average blood flow and glucose utilization in the brain as a whole were unaffected. These results show that high circulating levels of epinephrine similar to those accompanying glucoprivation alter neither local nor overall CBF and glucose utilization and cannot explain the increases in CBF associated with glucoprivation.