AJP - Heart and Circulatory Physiology, Vol 244, Issue 2 266-H272, Copyright © 1983 by American Physiological Society
Effects of gamma-aminobutyric acid on neural regulation of the canine sinus node
B. H. Neely, G. R. Hageman and T. N. James
The direct effects of gamma-aminobutyric acid (GABA) on the sinus node and
its neural regulation were studied by selective perfusion of the sinus node
artery (SNA) in 26 open-chest pentobarbital-anesthetized dogs. GABA
(1-1,000 micrograms/ml, 2 ml, SNA) produced no direct effect on intrinsic
sinus rate, but in several experiments (at 1 microgram/ml) it produced an
inconsistent augmentation of the sinus tachycardia due to right stellate
stimulation. At all other concentrations tested (10-1,000 micrograms/ml),
GABA did not significantly alter the sinus node response to stellate
stimulation. Local alpha-receptor blockade with phentolamine or muscarinic
receptor blockade with atropine through the SNA prior to the perfusion of
GABA did not change the sinus node responses. GABA (10-1,000 micrograms/ml,
2 ml, SNA) significantly attenuated (by 45-80% of control) the sinus
bradycardia due to stimulation of the right vagosympathetic trunk. The
sinus node response to selective perfusion of norepinephrine or
acetylcholine (0.01 micrograms/ml, 2 ml, SNA) was not affected by GABA. The
stellate augmentation (when present) and vagal attenuation were both
antagonized by perfusion of picrotoxin (1,000 micrograms/ml, 2 ml, SNA). It
is concluded that GABA does not exert any direct effect on the sinus node
but may indirectly influence sinus rate by an effect on local nerves or
ganglia.
