The effects of cold stress on respiration of diaphragm muscle

Abstract

The mechanism of the stimulating effect of short-term cold exposure of animal on tissue respiration has been studied. Oxygen consumption by a piece of the rat diaphragm muscle, fixed in a frame and put into a polarographic cell, was measured with an oxygen electrode. It is found that 13 min exposure of the rat to an air temperature of +2°C induces (1) an increase in respiration rate in the diaphragm tissue, (2) a decrease in stimulation of respiration by dinitrophenol (DNP) and (3) a decrease in the sensitivity of respiration to amytal. The maximal respiration rate observed in the presence of 40 μM DNP is unaffected. Acclimation for two weeks of rats at +2°C does not influence the measured parameters. Effects similar to those produced by short-term cold exposure can be obtained by treatment of the cold acclimated animals with norepinephrine. In non-acclimated rats, norepinephrine is ineffective. The effects of cold exposure (or norepinephrine) can be reproduced on the diaphragm from a non-treated animal by the addition of 0.2 mM oleate or 10 mM pyruvate to the incubation medium. All effects of cold exposure or norepinephrinein vivo, or oleate and pyruvatein vitro are inhibited by oubain or replacement of Na⁺ by Li⁺ in the incubation mixture. The role of fatty acids and Na,K ATP-ase in the thermoregulatory responses of the tissue respiration is discussed.