Oxygen uptake by jejunal strips of rat in the absence of Na+ (replaced by mannitol)

Abstract

The O2 uptake of jejunal strips has been determined in Krebs-Ringer-Trismedia with or without the presence of Na+. The total substitution of Na+ produced a pronounced decrease in O2 consumption, followed by respiratory cessation within 3 or 4 hours. This effect is only parcially reversed by the replacement of Na+. The addition of glucose or fructose to a medium with Na+, enhances consumption of O2, but the increase is much lower when the sugars are added to a medium without Na+ (replaced by mannitol). Ouabain, at very high concentrations (10-4 M to 6 X 10-3 M) inhibit the O2 uptake in a medium with Na+, independent of the presence or absence of glucose or fructore; no appreciable effect is found when the medium is Na+- free. The highest inhibition reached with ouabain is much below those obtained by the suppression of Na+ (mannitol). The results lead to the conclusion that replacement of Na+ by mannitol, does not only decrease O2, uptake by the sim­ ple standstill of the Na+ pump, but also inducing durable alterations in the oxidative metabolism of the tissues.