[en] Tyramine (T) induces coma in phenelzine-treated dogs. The objective of the present investigation was to examine the influence of T in MAO-inhibited dogs on the kinetics of Tc-99m-DTPA during its first passage through the brain by nuclear imaging. The study began with anesthetized dogs (n=10) in a supine position over the camera detector. Data acquisition was started simultaneously following the rapid intracarotid injection of Tc-99m-DTPA (30 mCi) and 60 0.5 second images of the brain were taken. T induced increased uptake with a concomittant impairment in the elimination of Tc-99m-DPTA from the brain of these treated animals as compared to controls. This was accompanied by an appreciable reduction in hemispheric cerebral blood flow (CBF) (56 +/- 19 vs 110 +/- 16 ml/100g/min). Increased cerebrovascular permeability of Tc-99m-DTPA and decreased CBF correlated significantly with development of intracranial hypertension and elevation in CSF catecholamines in these animals. T may have implication in the development of cerebral edema of Reye's syndrome