AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 2 221-R227, Copyright © 1984 by American Physiological Society
Effect of bilateral vagotomy on the ventilatory responses of the water snake Nerodia sipedon
R. K. Gratz
The effects of bilateral vagotomy on pulmonary ventilation, O2 consumption,
and heart rate were determined for the water snake, Nerodia sipedon,
breathing room air at 15, 25, and 30 degrees C and breathing 5.2% CO2 in
air at 25 degrees C. At all body temperatures, vagotomy resulted in a four-
to sevenfold increase in tidal volume in snakes breathing room air. At the
same time, ventilatory frequency decreased such that pulmonary ventilation
was unchanged after vagotomy. Heart rate increased approximately 1.5 times
after vagotomy, but O2 uptake was unchanged. The air convection requirement
decreased similarly with increasing body temperature in both intact and
vagotomized snakes. Arterial pH values were similar to those of intact
snakes measured in a previous study and decreased by -0.013 U/degrees C.
Since this occurs despite elimination of peripheral chemoreceptor input, it
is suggested that the temperature compensation is a centrally controlled
process. In intact snakes, breathing CO2 resulted in a fourfold increase in
ventilation. Elimination of peripheral receptor input by vagotomy resulted
in a loss of this ventilatory response to CO2 breathing. This means that
peripheral receptors are required for a response to changes in arterial CO2
partial pressure and pH. Snakes thus differ from turtles and mammals in
that central chemoreceptors alone are unable to produce the ventilatory
response to inspired CO2.
