Factors affecting the utilization of ketone bodies and other substrates by rat jejunum: effects of fasting and of diabetes.

1. The utilization of some metabolic fuels has been measured in vitro in a preparation of rat jejunum to which the substrates were supplied via the perfusate flowing through the vascular bed. 2. In jejunum from 48 hr-fasted rats, the combined rates of utilization of 1 mM-acetoacetate and 2mM-D-3-hydroxybutyrate are similar to that of 7.5 mM-glucose. 3. The utilization of glucose is reduced in jejunum from animals fasted for 48 hr (45--63% reduction) and also from animals after 3--6 days of diabetes induced by streptozotocin (29% reduction). The addition of ketone bodies or of Na-oleate to the vascular perfusate does not reduce the utilization of glucose by the jejunum of either fed or 48 hr fasted rats. 4. Ketone bodies in the vascular perfusate reduce the oxidation of glucose by the jejunum of fed rats. In the jejunum of 48 hr-fasted rats, ketone bodies completely inhibit the oxidation of glucose so that all the glucose utilized by the tissue is converted to lactate. 5. The findings are discussed in relation to other work and it is concluded that substrates for the oxidative metabolism of the jejunum of fasted rats are likely to be ketone bodies, glutamine and fatty acids; at the same time the utilization of glucose is reduced and its oxidation completely abolished.