Journal of Applied Physiology, Vol 68, Issue 6 2419-2425, Copyright © 1990 by American Physiological Society
Effect of serotonin on expiratory pulmonary resistance in cats
M. Skaburskis, F. Shardonofsky and J. Milic-Emili
Meakins-Christie Laboratories, McGill University, Montreal, Quebec, Canada.
In five anesthetized paralyzed cats, mechanically ventilated with tidal
volumes of 36-48 ml, the isovolume pressure-flow (IVPF) relationships of
the lung were studied under control conditions and during serotonin-induced
bronchoconstriction. At the end of a tidal inspiration, airway opening
pressure was set between +3 and -15 cmH2O for single tidal expirations.
After control measurements, animals were treated with progressively
increasing doses of intravenous serotonin (10, 20, 50, and 100
micrograms.kg-1.min-1) and all measurements were repeated at each dose. No
animal became flow limited during passive expiration against atmospheric
pressure. Disregarding flow-limited segments, IVPF plots for three lung
volumes showed that the resistive pressure-flow relationships were
curvilinear under all conditions, thus fitting Rohrer's equation. Under
control conditions and during the lowest dose of serotonin, the volume
dependence of pulmonary resistance (RL) tended to balance its flow
dependence so that during lung deflation against atmospheric pressure RL
remained nearly constant. However, as bronchoconstriction became more
pronounced, RL often increased disproportionately at the lower lung
volumes. Changes in expiratory RL with serotonin relative to control values
varied according to the flow rates used to make comparisons. The technique
used to determine RL will partly determine the results obtained.
