AJP - Heart and Circulatory Physiology, Vol 250, Issue 3 498-H502, Copyright © 1986 by American Physiological Society
Unilateral and bilateral sympathetic effects on cerebral blood flow during normocapnia
D. W. Busija
The purposes of this study were to 1) determine the effects of unilateral
and bilateral sympathetic stimulation on cerebral blood flow (CBF) during
normocapnia and 2) explore the mechanism by which bilateral effects are
greater than unilateral effects. In anesthesized rabbits, CBF (15-microns
microspheres) and internal carotid artery blood flow (ICBF) were determined
during a prestimulation period and electrical stimulation of one or both
superior cervical ganglia (8 or 16 Hz, 10 V, 2 ms). Resting CBF ranged from
26 to 34 ml X min-1 X 100 g-1. Unilateral stimulation did not reduce CBF at
8 Hz, but stimulation at 16 Hz reduced ipsilateral blood flow to the
cerebrum by 21 +/- 5% (n = 6 from each group). In contrast, bilateral
stimulation reduced blood flow to cerebrum by 22 +/- 5 and 40 +/- 4% at 8
and 16 Hz, respectively (P less than 0.05, unilateral vs. bilateral; n = 6
for each group). Similarly, unilateral stimulation at 8 Hz did not reduce
ipsilateral ICBF or affect contralateral ICBF. However, bilateral
stimulation at 8 Hz reduced ICBF by 51 +/- 6% on both sides. We conclude
that 1) bilateral effects of sympathetic nerves on CBF are greater than
unilateral effects, and 2) this difference in response may be due to
activation of two overlapping sets of sympathetic nerves and release of
more neurotransmitter during bilateral sympathetic stimulation.
