AREGU April 47/4

Weber, Jean-Michel, and Deena S. Shanghavi. Regulation of glucose production in rainbow trout: role of epinephrine in vivo and in isolated hepatocytes. Am J Physiol Regulatory Integrative Comp Physiol 278: R956–R963, 2000.— The rate of hepatic glucose production (Ra glucose) of rainbow trout (Oncorhynchus mykiss) was measured in vivo by continuous infusion of [6-3H]glucose and in vitro on isolated hepatocytes to examine the role of epinephrine (Epi) in its regulation. By elevating Epi concentration and/or blocking b-adrenoreceptors with propranolol (Prop), our goals were to investigate the mechanism for Epi-induced hyperglycemia to determine the possible role played by basal Epi concentration in maintaining resting Ra glucose and to assess indirect effects of Epi in the intact animal. In vivo infusion of Epi caused hyperglycemia (3.75 6 0.16 to 8.75 6 0.54 mM) and a twofold increase in Ra glucose (6.57 6 0.79 to 13.30 6 1.78 μmol ·kg21 ·min21, n 5 7), whereas Prop infusion decreased Ra from 7.65 6 0.92 to 4.10 6 0.56 μmol ·kg21 ·min21 (n 5 10). Isolated hepatocytes increased glucose production when treated with Epi, and this response was abolished in the presence of Prop. We conclude that Epi-induced trout hyperglycemia is entirely caused by an increase in Ra glucose, because the decrease in the rate of glucose disappearance normally seen in mammals does not occur in trout. Basal circulating levels of Epi are involved in maintaining resting Ra glucose. Epi stimulates in vitro glucose production in a dose-dependent manner, and its effects are mainly mediated by b-adrenoreceptors. Isolated trout hepatocytes produce glucose at one-half the basal rate measured in vivo, even when diet, temperature, and body size are standardized, and basal circulating Epi is responsible for part of this discrepancy. The relative increase in Ra glucose after Epi stimulation is similar in vivo and in vitro, suggesting that indirect in vivo effects of Epi, such as changes in hepatic blood flow or in other circulating hormones, do not play an important role in the regulation of glucose production in trout.