Effects of oleic acid infusion on plasma free fatty acids and blood ketone bodies in the fasting rat.

Oleic acid emulsions stabilized with albumin were infused into fasted rats. Blood samples taken before and during infusion were analyzed for free fatty acids (FFA), ketone bodies, glucose, and insulin. Turnover rates of FFA and ketone bodies were also determined using constant infusion of radioactive tracers. During oleic acid infusions at a rate of 2 mumoles/min/100 g body weight, FFA concentrations increased for a short time and then decreased to preinfusion levels. The decreases in concentrations were due to decreases in the endogenous rates of appearance of FFA into the blood. When oleic acid was infused at a rate of 3.5 mumoles/min/100 g body weight, FFA concentrations increased and remained elevated throughout the infusion. Ketone body concentrations more than doubled during infusions at 2 and 3.5 mumoles/min/100 g body weight and showed no signs of decreasing even when FFA concentrations decreased. Insulin concentrations doubled during infusion and glucose concentrations decreased. Insulin injected during infusion had little effect on concentrations of FFA or ketone bodies. It was concluded that infusions of oleic acid inhibit adipose tissue lipolysis and increase blood ketone concentrations in intact fasted rats. The injection of insulin does not inhibit ketogenesis when blood FFA levels are maintained by infusion.