The Role of Glucagon in Regulating Chicken Hepatic Malic Enzyme and Histidase Messenger Ribonucleic Acid Expression In Response to an Increase in Dietary Protein Intake

Abstract

Increased dietary protein intake rapidly (3 h) decreases hepatic malic enzyme and increases hepatic histidase mRNA expression in broiler chicks. A series of experiments was conducted to determine the role that glucagon or a specific mixture of dietary amino acids might have in regulating the rapid changes in mRNA expression of these enzymes, when dietary protein intake is increased. Three hours after the injection of glucagon (240 microg/kg of BW) into the brachial vein of broiler chicks, hepatic malic enzyme mRNA expression was significantly lower and hepatic histidase mRNA expression was significantly greater than the level detected in saline-injected chicks. In addition, broiler chicks fed a high (40 g/ 100 g of diet) protein diet had significantly higher plasma glucagon levels at 1 and 3 h after initial access to this diet than broiler chicks fed a basal (22 g/100 g of diet) protein diet. The plasma glucagon concentration, however, was not different between the chicks fed the 2 dietary protein levels at 2 h after the initial access to the 2 diets. When a mixture of indispensable or dispensable amino acids was added to the basal diet to equal the concentrations of the individual indispensable or dispensable amino acids in the high protein diet, hepatic mRNA expression of malic enzyme and histidase were intermediate to the expression found in chicks fed the basal and high protein diet. The results indicate that glucagon may mediate the changes in the mRNA expression of malic enzyme and histidase in response to dietary protein intake and that total amino acid intake rather than the ingestion of specific amino acids regulates the mRNA expression of malic enzyme and histidase in chicks.

Phenylalanine-pyruvate aminotransferase activity in chicks subjected to phenylalanine imbalance or phenylalanine toxicity

“…High dietary concentrations of protein appear to increase glucagon secretion in mammals (Balage et al, 1986;Charlton et al, 1996;Gannon and Nuttall, 2004). Chendrimada et al (2006) observed increased plasma glucagon concentrations within 1 and 3 h but not at 2 h after feeding broiler chicks a diet containing 40% protein as compared with 13% protein. In previous studies in this laboratory, overnight-fasted Leghorn chicks were given access to a 19% CP diet containing nutritionally adequate or surfeit levels of all indispensable AA or the same diets supplemented with a 13.3% mixture of indispensable AA, NaHCO 3 , and glucose (Keene and Austic, 2001;Keene, 2002).…”

“…No differences in plasma glucagon concentrations between the 2 groups of chicks were detected during a 3-to 4-h period after the chicks had been given access to the diets in 3 experiments. The variable response to a 27% increment in dietary protein among the 3 sampling periods in the study of Chendrimada et al (2006) and the results of the experiments of Keene (2002) involving the AA supplement suggest that it may be difficult to detect effects of dietary protein on glucagon secretion in chickens. It is not clear whether glucagon is involved in the regulation of chicken PAT.…”

High amylose to amylopectin ratios in nitrogen-free diets decrease the ileal endogenous amino acid losses of broiler chickens

“…It is interesting to note that the glucagon level was significantly decreased in all NFD treatments compared to the control, as insulin and glucagon are normally perceived to operate in an opposite manner in mammals. This could be related to the nutritional composition of NFD, since there are positive relationships between dietary protein levels and plasma glucagon in chickens ( Chendrimada et al., 2006 ), and exposure to the exogenous glucose has been found to suppresses glucagon secretion ( Ma et al., 2005 ).…”