The effect of ouabain on metabolic rate in guinea-pigs: estimation of energy cost of sodium pump activity.

1. The effect of different doses of ouabain, an inhibitor of the sodium pump, or saline (9 g sodium chloride/1; the vehicle) on the metabolic rate of guinea-pigs weighing 500 g was measured by indirect calorimetry for 120 min. 2. Ouabain (0.02-0.07 nmol/g body-weight) decreased the oxygen consumption in a dose-related manner. When higher doses of ouabain (0.10 nmol/g body-weight or greater) were injected the animals were observed to shiver. Ouabain (0.07 nmol/g body-weight) reduced Na+,K+-ATPase (EC 3.6.1.3) activity of liver, kidney and skeletal muscle by 18.0 (SE 6.6), 21.5 (SE 6.0) and 21.9 (SE 6.8)% respectively. An Eadie-Hofstee plot of percentage decrease in O2 consumption v. percentage inhibition divided by dose of ouabain showed that maximal inhibition of O2 consumption was 39.4%. 3. It is concluded that Na pump activity contributed to about 40% of the resting O2 consumption.