Hormonal and nutritional regulation of phosphoenolpyruvate carboxykinase mRNA levels in chicken kidney.

In chickens, the kidney possesses a distinct cytosolic phosphoenolpyruvate carboxykinase activity which is not found in the liver. This activity is subject to long-term regulation by diet and changes in acid-base status. The activity is increased during starvation or metabolic acidosis. In addition, an unidentified component of some standard chicken diets results in altered activity. Using a specific cDNA probe the abundance of PEPCK mRNA has been determined in chicken kidney in vivo and in vitro. The abundance of PEPCK mRNA in chicken kidney increases during starvation and is rapidly decreased after refeeding carbohydrate. In isolated kidney tubules the abundance of the mRNA is increased after incubation with glucocorticoids, dibutyryl cAMP or hormones acting via changes in the concentration of cAMP (parathyroid hormone, epinephrine). Phorbol esters or hormones acting via calcium-dependent mechanisms were without effect. The results support the hypothesis that in the chicken the kidney is the major site of gluconeogenesis from substrates other than lactate and thus plays an important role in the maintenance of glucose homeostasis.