The effects of fasting on body composition, glucose turnover, enzymes and metabolites in the chicken.

Chickens (1,200 g) were fasted 1, 4, or 8 days. Significant decreases occurred in total body protein and fat with fasting, with the greatest energy loss from fat. Glucose production determined with either [2-3H] or [6-3H] glucose injected simultaneously with [U-14C] glucose remained constant with fasting at 10 to 13 mg/minute/kg body weight which is much higher than reported for mammals. Blood lactate and glycerol were unchanged with fasting, while pyruvate increased and plateaued. Plasma alanine, serine and glycine levels were extremely high compared to values in fasted mammals. Blood beta-hydroxybutyrate increased dramatically with fasting (350 to 3,500 nm/ml), while acetoacetate remained constant. The hepatic lactate: pyruvate ratio was unchanged with fasting, while the beta-hydroxybutyrate:acetoacetate ratio increased. These ratios have been reported to influence phosphoenolpyruvate (PEP) and glucose production in mammals. Hepatic and renal phospyoenolpyruvate carboxykinase (PEPCK) levels remained constant, while hepatic lactate dehydrogenase increased with fasting. Beta-Hydroxybutyrate dehydrogenase levels were very low at all times. The results indicate little glucose sparing adaptation per kg in the fasting chicken.