Abstract
The reactivity of pial arteries to local changes in pH, ion activity and alpha sympathetic agents was investigated during recovery from 1 hour's ischemia using a topical application on filter paper.
Cats were anesthetized with pentobarbital sodium and were submitted to one hour's complete cerebral ischemia by intrathoracic arterial clamping in combination with induced hypotension. Upon recirculation after one hour of ischemia, CBF increased above the preischemic level with marked dilatation of the pial vessels. Hyperemia lasted up to about one hour after recirculation, and was followed by delayed decrease in cerebral blood flow (postischemic hypoperfusion). The pial arteries at this time constricted by more than 20% indicating that the reduction in blood flow was due to an increased vascular tone. During this phase the vascular reactivity to pH and ion activity was distinctly reduced compared with that in normal state.
Blocking of calcium ions by EDTA or the topical application of high concentration of phentolamine, on the other hand, showed marked dilatation of the pial arteries up to 130% and the constricting effect of norepinephrine was similar to that in controls.
From the results obtained in this study, it is concluded that ischemic vessels are still able to respond to the topical application of pharmacological agents, although the reactivity to the changes in pH or ion activity is distinctly reduced. Failure of improving cerebral blood flow after ischemia by systemic administration of vasoactive drugs, therefore, seems to be due to the impermeability of the blood brain barrier rather than to the postischemic unresposiveness of pial arteries to these drugs.
