AJP - Heart and Circulatory Physiology, Vol 265, Issue 6 1856-H1863, Copyright © 1993 by American Physiological Society
Continuous pulmonary C-fiber stimulation produces sustained reflex cardiovascular depression
E. R. Schertel and D. A. Allen
Department of Veterinary Clinical Sciences, Ohio State University, Columbus 43210.
We used an isolated perfused in situ left lung preparation to evaluate the
hemodynamic response to specific pulmonary C-fiber stimulation with
capsaicin in two groups of anesthetized dogs. In one group (n = 6),
continuous administration of capsaicin at 5 micrograms.kg-1.min-1 into the
isolated pulmonary circulation produced sustained (20 min) reflex decreases
in mean arterial pressure, cardiac output, maximal left ventricular rate of
pressure over time, and heart rate. These effects were abolished by
vagotomy. In a second group (n = 5) of atropinized dogs, a mild hemorrhage
was first performed in each dog during control conditions (capsaicin
vehicle administration). The hemorrhage was performed by removing 10% of
blood volume over 3 min and then replacing this blood 3 min later. After
reinfusion and stabilization, the mild hemorrhage was repeated during
continuous administration of capsaicin (6.0 +/- 1.0 microgram.kg-1.min-1)
into the isolated pulmonary circulation. The decrease of mean arterial
pressure in response to hemorrhage was significantly greater during
capsaicin administration than during control conditions. Lung denervation
prevented the effect of capsaicin administration on the response to
hemorrhage. We concluded that continuous pulmonary C-fiber stimulation
produces sustained cardiovascular depression and compromises the
hemodynamic response to mild hemorrhage in dogs. This latter effect may
represent a central alteration of baroreflex gain.
