The rate of oxidation of 14C-labelled fatty acids and of ketone bodies was measured in isolated pancreatic islets of obese-hyperglycaemic mice (ob/ob). The following main observations were made. 1. Octanoate, palmitate and oleate were all converted into CO2 by the pancreatic islets. Octanoate was oxidized with the highest rate followed by palmitate and oleate. 2. The rate of oxidation of 0.7 mM-palmitate was 3.1 pmol/h per mug drug weight. This was decreased by 50% in the presence of 16.7 mM-glucose. The rate of palmitate oxidation was also inhibited by 2-bromostearate. The palmitate oxidation showed a concentration-dependent increase, which was most marked between 0.25 and 1.0 mM. 3. Octanoate (5 mM) had no effect on the rate of oxidation of 3.3 mM- glucose. 4. Acetoacetate (5 mM) and D-3-hydroxybutyrate (5 mM) were oxidized at rates of 5.9 and 5.4 pmol/h per mug dry weight respectively. These rates were less than 10% of those found in kidney-cortex slices. The magnitude of the oxidation rates found for fatty acids and for ketone bodies suggest that these substrates represent important metabolic fuels for the pancreatic B-cells.

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