Blood D-3-hydroxybutyrate and the regulation of plasma concentrations of free fatty acids in the fasted rat.

Acetoacetate or DL-3-hydroxybutyrate 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 acetoacetate or DL-3-hydroxybutyrate, blood concentrations of total ketone bodies doubled. While the HBA/AcAc ratios remained constant in rats infused with DL-3-hydroxybutyrate, the ratios decreased significantly during infusion of acetoacetate, reflecting increases in acetoacetate concentrations without proportionate increases in concentrations of D-3-hydroxybutyrate. Blood concentrations of free fatty acids decreased more rapidly in the rats infused with DL-3-hydroxybutyrate than in the rats infused with acetoacetate. The decrease in free fatty acid concentrations was related to increases in blood D-3-hydroxybutyrate in both the DL-3-hydroxybutyrate-infused rats and in the acetoacetate-infused rats. Plasma immunoreactive insulin concentrations were significantly higher in the DL-3-hydroxybutyrate-infused rats than in the acetoacetate-infused rats. Acetoacetate and DL-3-hydroxybutyrate 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. From these experiments it was concluded that increases in blood concentrations of D-3-hydroxybutyrate were more effective than acetoacetate in causing decreases in free fatty acid concentrations in the fasting rat. The pancreas is required for this effect.