The local influence of sympathetic stimulation on the cerebral circulation
during acute hypertension was investigated in anesthetized rats. From
initial studies, intravenously administered angiotensin II was selected as
the pressor agent. Local cerebral blood flow was measured with
[14C]iodoantipyrine autoradiography during 1) unilateral electrical
stimulation of the superior cervical ganglion plus moderate hypertension
[mean arterial blood pressure (MABP) 162 +/- 2 mmHg], 2) unilateral
stimulation plus severe hypertension (MABP 177 +/- 4 mmHg), and 3)
unilateral preganglionic sympathetic nerve section (denervated) plus severe
hypertension (MABP 186 +/- 4 mmHg). During moderate hypertension, blood
flow was rather homogeneous and sympathetic stimulation produced modest
(7-15%) regionally specific reductions in flow ipsilateral to the
stimulation (P less than 0.05). During severe hypertension: 1) focal areas
of marked hyperemia occurred throughout the brain, 2) local blood flow was
similar within innervated and denervated hemispheres, and 3) with
sympathetic stimulation the volume of hyperemic tissue was reduced
ipsilaterally and blood flow was decreased by 7-25% in areas of basal
ganglia, cerebral cortex, limbic system and thalamus. To conclude, 1) the
local cerebral autoregulatory response is highly dependent on whether the
area becomes hyperperfused and 2) sympathetic stimulation decreases brain
blood flow by modestly reducing local tissue perfusion and by lessening the
volume of extreme hyperemia.
U. I. Tuor
Division of Neonatology, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada.
Am J Physiol Heart Circ Physiol 263: H511-H518, 1992;