Hormonal control of gluconeogenesis in rainbow trout hepatocytes: Regulatory role of pyruvate kinase

Gluconeogenesis from lactate in hepatocytes from rainbow trout is activated by glucagon and inhibited by insulin in a dose‐dependent fashion. The maximal responses to both hormones occur within their probable physiological concentration ranges. Gluconeogenic activation by glucagon is accompanied by a profound inhibition of pyruvate kinase activity. This is reflected in increases in both the S0.5 and nH for phosphoenolpyruvate and increased sensitivity to inhibition by MgATP compared to the enzyme isolated from cells not treated with hormone (control). Gluconeogenic inhibition by insulin is accompanied by activation of pyruvate kinase activity. This is observed as decreases in both the S0.5 and nH for phosphoenolpyruvate and a decreased sensitivity to inhibition by MgATP compared to enzyme isolated from control cells. These results indicate that insulin and glucagon are involved in the regulation of hepatic gluconeogenesis in trout and that their effects are mediated, at least partly, through the control of pyruvate kinase activity.