The Journal of clinical investigation
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The metabolism of FFA and ketone bodies was studied in fasted rats by infusing at a constant rate tracer amounts of FFA-(3)H, beta-hydroxybutyrate-(14)C or acetoacetate-(14)C for periods up to 2 hr. Blood that was removed for analyses was replaced by continuous transfusion. The rates of turnover of FFA, beta-hydroxybutyrate, and acetoacetate in rats fasted for 2 days were, respectively, 3.2, 5.6, and 2.5 mumoles/100 g body weight per min. ⋯ Insulin injection (20 mU i.v.) lowered the plasma ketone body concentration in these animals. Studies using beta-hydroxybutyrate-(14)C showed that insulin (50 mU i.v.) decreased ketogenesis in the presence of a sustained high plasma FFA concentration and had no effect on uptake of circulating ketone bodies. The results indicate that plasma FFA concentration is not the sole determinant of plasma ketone body concentration and that insulin can suppress ketone body production through some means other than lowering plasma FFA concentration.