Journal of Applied Physiology, Vol 50, Issue 2 428-434, Copyright © 1981 by American Physiological Society
Prostaglandin E1 uptake by isolated cat lungs perfused with physiological salt solution
J. H. Linehan, C. A. Dawson and V. M. Wagner-Weber
The instantaneous extraction of prostaglandin E1 (PGE1) was measured after
a bolus injection of PGE1 and [14C]dextran in to the pulmonary artery of
isolated cat lungs perfused with a physiological salt solution
[Krebs-Ringer-bicarbonate buffer (KRB)]. The extraction ratio vs. time
curves exhibited characteristic shapes. For low injected doses of PGE1, the
extraction ratios were constant early in time, whereas for high doses, they
were concave upward. To evaluate the data, we used a model assuming
homogeneous perfusion and a saturable uptake mechanism (Michaelis-Menten
kinetics) for the PGE1. The model was used in a linear regression analysis
to estimate Vmax and Km. The kinetic parameters were compared with our
previous results for blood-perfused lungs, and it was found that the values
of Km were significantly smaller than in blood-perfused lungs but that the
values of Vmax were not significantly different. These results were
consistent with the observation that PGE1 uptake was greater in KRB- than
in blood-perfused lungs when the dose of PGE1 was low but that the
difference disappeared at high doses. The absence of plasma protein binding
in KRB-perfused lungs may be responsible for the lower Km.
