Regulation of messenger ribonucleic acid expression for gluconeogenic enzymes during glucagon infusions into lactating cows

The effects of glucagon infusions on expression of mRNA for enzymes that re gulate gluconeogenesis were studied in lactating cows. Normal cows and cows with fatty liver that were susceptible to ketosis were assigned to either glucagon-treated or control groups. Glucagon at 0 or 10 mg/d was infused fo r 14 d beginning at d 21 postpartum. In normal cows, glucagon infusions inc reased concentrations of both plasma glucagon and glucose, which caused pla sma insulin to increase. Consequently, hepatic phosphoenolpyruvate carboxyk inase mRNA decreased during wk 1 of glucagon infusions. Glucagon infusions into cows with fatty liver also increased plasma glucagon and glucose, but concentrations of plasma insulin and hepatic phosphoenolpyruvate carboxykin ase mRNA did not change. More phosphoenolpyruvate carboxykinase mRNA was pr esent in the livers of cows with fatty liver than in livers of normal cows. In a follow-up experiment with midlactation cows, 3.5-h infusions of gluca gon at 14 mg/d increased plasma glucose and insulin and decreased plasma no nesterified fatty acids and hepatic glycogen. Hepatic phosphoenolpyruvate c arboxykinase mRNA was decreased 41%, pyruvate carboxylase mRNA was increase d 50%, but fructose-1,6-bisphosphatase mRNA did not change. We conclude tha t the expression of the hepatic phosphoenolpyruvate carboxykinase gene in n ormal cows is inhibited by insulin to balance elevated carbohydrate status during glucagon infusions; however, inhibited expression of hepatic phospho enolpyruvate carboxykinase mRNA probably is not involved in the pathogenesi s of lactation ketosis.