Glucagon increases hepatic mRNA concentrations of ureagenic and gluconeogenic enzymes in early-lactation dairy cows

Abstract

Exogenous glucagon increases hepatic glucose synthesis in part by increasing hepatic extraction of amino acids from blood for conversion to glucose. To examine the role of glucagon in orchestrating gene expression of gluconeogenic and ureagenic enzymes, we determined the mRNA concentrations of key hepatic ureagenic and gluconeogenic enzymes at d 11, 15, and 22 postpartum in multiparous Holstein cows that received 0 or 5 mg of glucagon in 60 mL of saline by subcutaneous injection every 8 h for 14 d starting on d 8 postpartum. On d 11 postpartum, glucagon increased the hepatic mRNA concentrations for all measured ureagenic enzymes (carbamoylphosphate synthetase I, ornithine transcarbamylase, and argininosuccinate synthetase) and gluconeogenic enzymes (pyruvate carboxylase and cytosolic and mitochondrial forms of phosphoenolpyruvate carboxykinase) and increased or tended to increase mRNA concentrations of gluconeogenic enzymes on d 15 postpartum but not on d 22. The effect of glucagon to increase mRNA concentrations of ureagenic and gluconeogenic enzymes was limited to times when concentrations of plasma insulin were not increased. Our results suggest that hepatic gene expression of key ureagenic and gluconeogenic enzymes in early-lactation dairy cows is responsive to hormonal regulation by glucagon.