Journal of Applied Physiology, Vol 53, Issue 3 677-684, Copyright © 1982 by American Physiological Society
Influence of blood and plasma flow rate on kinetics of serotonin uptake by lungs
D. A. Rickaby, C. A. Dawson and J. H. Linehan
Serotonin extraction following a bolus injection of serotonin and a
nonpermeating indicator into the pulmonary artery can be evaluated using a
model that represents the saturable uptake of serotonin by Michaelis-Menten
kinetics. By use of this model Km, Vmax, and a perfusion parameter, alpha,
can be determined by multiple linear regression analysis of the
time-concentration data. Kinetic and perfusion parameters were obtained
using data from isolated dog lung lobes in which plasma flow rate was
changed by changing the pump flow rate in blood- or plasma-perfused lobes
or by keeping the pump flow rate constant and removing the blood cells. The
calculated Vmax was reproducible and flow independent over the range of
flow rates used in the study. The calculated Km was more sensitive than
Vmax to small variations in experimental data and was independent of flow
at flow rates greater than about one-half the normal cardiac output per
gram of lung tissue. The perfusion parameter alpha was lower in the
plasma-perfused lobes, reflecting more homogeneous perfusion in the absence
of cells. The results suggest that this approach will be useful for
separating changes in the kinetics of serotonin uptake by endothelial cells
from effects of changes in flow and perfusion heterogeneity.
