Blood Metabolites and Glucose Metabolism in the Fed and Fasted Chicken

Abstract

The effect of fasting on blood metabolites and glucose metabolism in the chicken was studied. Parameters of glucose metabolism were estimated in vivo using a single injection of [2-³H]-glucose or [6-³H]-glucose in combination with [U-¹⁴C]-glucose. Plasma glucose, blood lactate and blood acetoacetate levels were not significantly changed in chickens fasted for 72 hours. Pyruvate levels in chickens fasted for 24 hours were higher than those observed in blood from birds fasted 0 or 72 hours. Further, the lactate to pyruvate ratio was lower in chickens fasted for 24 or 72 hours than in fed chickens. Fasting chickens for 24 or 72 hours resulted in three- to fivefold increase in blood β-hydroxybutyrate levels and a significant increase in the β-hydroxybutyrate to acetoacetate ratio. Plasma levels of alanine and serine were increased after a 24 hour fast but were not further changed when fasting was extended to 72 hours. Plasma aspartate and glutamate levels were not significantly changed in chickens fasted for 24 hours but were markedly decreased in chickens fasted for 72 hours. Plasma levels of glycine were significantly lower in chickens fasted 24 or 72 hours than in fed birds. Glucose replacement rates estimated with [2-³H]-glucose in chickens fasted 0, 24 and 72 hours were 14.3, 9.1 and 9.4 mg glucose/minute/kg body weight, respectively. Fasting up to 72 hours did not influence the total body glucose mass in the chickens. The degree of glucose-carbon recycling in 24-hour fasted chickens estimated by using [2-³H]- and [U-¹⁴C]-glucose or [6-³H]- and [U-¹⁴C]-glucose averaged 42% to 52% and 27% to 30%, respectively. These observations indicate that rate of glucose utilization in the chicken is rapid and that substantial recycling of glucose carbon occurs in fasted chickens.