AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 5 642-R650, Copyright © 1983 by American Physiological Society
Open-loop analysis of the pulmocutaneous baroreflex in the toad Bufo marinus
N. H. West and B. N. Van Vliet
In the conscious toad, Bufo marinus, heart rate responses to manipulations
of arterial pressure by vascular occlusion confirm that receptors sensitive
to changes in intravascular pressure are located in the pulmocutaneous
arteries. The cardiovascular responses to electrical stimulation of the
central end of the laryngeal branch of the vagosympathetic trunk indicate
that their afferents lie within this nerve. Inflation of an isolated
pulmocutaneous sac in conscious toads in which the contralateral laryngeal
nerve was cut resulted in a reduction of mean aortic pressure, with an
associated bradycardia in some animals. Maximum open-loop gain for the
relationship between sac pressure and aortic pressure was 0.35 +/- 0.06 (n
= 5), resulting in a predicted maximum closed-loop gain of 0.25 +/- 0.03.
Maximum gain occurred at 4.0-6.0 kPa, which was higher than the normal
range of mean pulmocutaneous pressures in conscious undisturbed B. marinus,
suggesting that the baroreceptors may be more effective in compensating for
a rise than for a fall in pressure. This functional characteristic of the
receptors suggests that not only may they modulate mean pressure in both
the systemic and pulmocutaneous circuits, but that they may be particularly
important in protecting the lung vasculature from excessive hydrostatic
pressures.
