AJP - Endocrinology and Metabolism, Vol 241, Issue 2 101-E107, Copyright © 1981 by American Physiological Society
Proteolysis in the rat lung: hypoxia and evidence for an inhibitor of proteolysis
M. J. Chiang, F. Kishi, P. Whitney and D. Massaro
We labeled proteins with [14C]phenylalanine in rats breathing air and
assessed the rate of proteolysis in the isolated ventilated lung by
measuring the accumulation of [14C]phenylalanine in the medium perfusing
the lung. Ventilation with 0% O2 decreased the rate of proteolysis and the
ATP content in the lung 60%. Medium from lungs ventilated with 0% O2, when
used to perfuse lungs ventilated with 95% O2, decreased the rate of
proteolysis 60% without lowering the ATP content of the lung. Correcting
the pH of "used" medium or dialyzing used medium did not decrease its
ability to inhibit proteolysis. Used medium from nonhypoxic lungs, or
exogenous lactate (50 mM), diminished proteolysis only 20%. In a cell-free
system the degradation by cathepsin D of radioactive lung proteins and
radioactive hemoglobin was decreased by used medium from hypoxic lungs. We
conclude that the hypoxic perfused lung releases a factor(s) that decreases
the rate of proteolysis in nonhypoxic lungs and that this factor may be a
protease inhibitor.
