Bobe G, Velez J C, Beitz D C, Donkin S S
Department of Animal Science, Iowa State University, Ames 50011, USA.
J Dairy Sci. 2009 Oct;92(10):5092-9. doi: 10.3168/jds.2009-2152.
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.
外源性胰高血糖素部分通过增加肝脏从血液中摄取氨基酸以转化为葡萄糖来增加肝脏葡萄糖合成。为了研究胰高血糖素在协调糖异生和尿素生成酶基因表达中的作用，我们测定了经产荷斯坦奶牛产后第11天、15天和22天关键肝脏尿素生成酶和糖异生酶的mRNA浓度。这些奶牛从产后第8天开始，每8小时皮下注射一次含0或5mg胰高血糖素的60mL生理盐水，持续14天。产后第11天，胰高血糖素增加了所有测定的尿素生成酶（氨甲酰磷酸合成酶I、鸟氨酸转氨甲酰酶和精氨琥珀酸合成酶）和糖异生酶（丙酮酸羧化酶以及磷酸烯醇式丙酮酸羧激酶的胞质和线粒体形式）的肝脏mRNA浓度，并且在产后第15天增加或趋于增加糖异生酶的mRNA浓度，但在第22天没有。胰高血糖素增加尿素生成酶和糖异生酶mRNA浓度的作用仅限于血浆胰岛素浓度未升高的时期。我们的结果表明，泌乳早期奶牛肝脏中关键尿素生成酶和糖异生酶的基因表达对胰高血糖素的激素调节有反应。
