AJP - Heart and Circulatory Physiology, Vol 242, Issue 5 790-H796, Copyright © 1982 by American Physiological Society
Cardiovascular responses to unilateral and bilateral stimulation of rabbit aortic nerves
H. O. Stinnett, F. J. Sepe and M. R. Magnusson
Reflex heart and mean arterial pressure (MAP) responses during unilateral
and bilateral electrical stimulation of the central end of the cut aortic
nerves were studied in 14 anesthetized closed-thorax rabbits. During
control of carotid intrasinus pressure (ISP), with ISP = MAP, heart rate
was 248 +/- 12 beats/min and fell -79 +/- 14, -61 +/- 16, and -117 +/- 16
beats/min during left (LAN), right (RAN), and bilateral (BAN) nerve
stimulation. MAP was 79 +/- 5 mmHg and fell -57 +/- 4 (LAN), -46 +/- 6
(RAN), and -65 +/- 4 mmHg (BAN). Responses were also determined following
blockade of cardiac vagal efferents (atropine) and then vagotomy (n = 4) or
vagotomy alone (n = 10). Results indicated that cardiac parasympathetic
effects of LAN and RAN stimulation were additive, whereas the respective
summation of cardiac and arterial vascular sympathetic effects were
mutually inhibitory. BAN stimulation at low (25 mmHg) and high (greater
than or equal to 125 mmHg) ISP levels resulted in different magnitudes of
MAP and heart rate responses before and after vagotomy and beta-receptor
blockade. These results indicated that summation was mutually inhibitory
for cardiac and vasomotor sympathetics when maximal stimulation of opposite
influence was applied to aortic and carotid afferents. However, arterial
baroreceptor afferents may summate differently at more normal blood
pressure conditions.
