Influence of diet on lactate, alanine and serine turnover and incorporation into glucose in the dog.

Four diets containing 0 to 62% of energy from carbohydrate and 24% to 48% of energy from protein were fed to young dogs. The influence of these diets on the turnover of [U-14C]-L-lactate, [U-14C]-L-alanine and [U-14C]-L-serine and on the incorporation of these gluconeogenic precursors into plasma glucose of the dog was established. Blood lactate levels were lowered when high-protein diets were fed but were not influenced by the level of carbohydrate in the diet or by a 48-hour fast. Plasma alanine and serine levels were elevated in dogs fed the high-protein diets and were lowered by a 48-hour fast. Turnover of lactate was increased in dogs fed high-carbohydrate diets whereas turnover of alanine and serine was increased in dogs fed the high-protein diets. Following a 48-hour fast, 14C-lactate conversion to plasma glucose was lower in dogs fed the high-protein diets than in dogs fed the lower protein diets whereas 14C-alanine and 14C-serine conversion to plasma glucose was increased in dogs fed the high-protein. Thus, the diet consumed altered the relative importance of these gluconeogenic precursors to the maintenance of plasma glucose.