BLOOD D-3-HYDROXYBUTYRATE AND REGULATION OF PLASMA CONCENTRATIONS OF FREE FATTY-ACIDS IN FASTED RAT

Acetoacetate [AcAc] or DL-3-hydroxybutyrate[HBA] were infused into fasted rats at rates comparable to the endogenous rate of ketone body release. Blood samples, taken before and during infusion, were analyzed for concentrations of ketone bodies, free fatty acids and immunoreactive insulin. During infusion of AcAc or DL-3-HBA, blood concentrations of total ketone bodies doubled. While the HBA/AcAc ratios remained constant in rats infused with DL-3-HBA the ratios decreased significantly during infusion of AcAc, reflecting increases in AcAc concentrations without proportionate increases in concentrations of D-3-HBA. Blood concentrations of free fatty acids decreased more rapidly in the rats infused with DL-3-HBA than in the rats infused with AcAc. The decrease in free fatty acid concentrations was related to increases in blood D-3-HBA in both the DL-3-HBA-infused rats and in the AcAc-infused rats. Plasma immunoreactive insulin concentrations were significantly higher in the DL-3-HBA-infused rats than in the AcAc-infused rats. AcAc and DL-3-HBA were infused into depancreatized, functionally hepatectomized fasted rats at rates comparable to those used in the intact fasted rats. Only small decreases in free fatty acid concentrations were observed during infusion. Increases in blood concentrations of D-3-HBA were more effective than AcAc in causing decreases in free fatty acid concentrations in the fasting rat. The pancreas is required for this effect.