Infusion of nicotinic acid stimulates leucine oxidation and inhibits protein synthesis in pigs before and during a meal.

Leucine metabolism was measured isotopically in immature female pigs to assess the effect of acute infusions of nicotinic acid (NA) on leucine kinetics in both the fed and fasting states. After an overnight fast, immature pigs were infused with 3H-alpha-ketoisocaproate (KIC) and 14C-leucine. After a 2-hour equilibration period, an infusion of either saline or 0.4 mg/kg.min of NA was begun. NA caused a decrease in plasma glucose and an increase in plasma glucagon. During the fasting period, NA increased KIC oxidation 2-fold over controls. After feeding, plasma free fatty acids (FFA) in both groups were equivalent, but KIC oxidation was still approximately 80% higher in NA-infused animals. In addition, NA stimulated proteolysis and inhibited protein synthesis during the meal. Because plasma FFA concentrations were equal during the fed period, it is unlikely that changes in FFA concentrations are responsible for the changes in leucine metabolism observal during NA infusion.