Glucose and Acetate Metabolism in Sheep at Rest and During Exercise

Abstract

Total entry rate of blood glucose and the rate of irreversible loss of blood acetate and its oxidation were examined in sheep at rest and walking on a horizontal treadmill at 5 km/h for 2 h. Sheep were given their daily ration of 1000 g chaff in 24 equal portions at hourly intervals and received multiple i.v. injections of [2-3H]glucose and i.v. infusions of [1-14C]acetate and NaH14CO3. At rest the total entry rate of blood glucose was 0.44 .+-. 0.03 mmol/min (values given as mean .+-. SEM [standard error of the mean] for 4 sheep); the glucose pool was 23 .+-. 1 mmol, and the rate of irreversible loss of blood acetate was 2.3 .+-. 0.1 mmol/min. During exercise the total entry rate of blood glucose was 0.84 .+-. 0.04 mmol/min; the glucose pool was 27 .+-. 2 mmol, and the rate of irreversible loss of blood acetate was 2.6 .+-. 0.1 mmol/min. Gluconeogenesis apparently increased markedly in response to exercise as indicated by the incorporation of 14C from blood bicarbonate into blood glucose. Despite the substantial increase in the rate of irreversible loss of blood bicarbonate (from 11.6 .+-. 1 to 20.2 .+-. 2 mmol C/min), and hence energy expenditure with exercise, only a slight change was recorded in the proportion of the irreversible loss rate of oxidized acetate.