Effects of Calcium Ions on the Activation of Gluconeogenesis by Norepinephrine in Perfused Rat Liver

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Abstract
The effects of calcium ions on the activation of gluconeogenesis by norepinephrine were studied in the perfused rat liver. The norepinephrine-mediated enhancement of gluconeo-genesis was accompanied by a transient increase in the reduction level of pyridine nucleotides. There was a positive correlation between the increases in the rate of glucose production and the reduction level of pyridine nucleotides induced by norepinephrine. These changes were “dose-dependent” with respect to the norepinephrine concentration from 5 nM to 1 μM and were mimicked by phenylephrine. The omission of calcium from the perfusate did not modify the basal rate of gluconeogenesis from lactate and pyruvate or the increased rate of glucose production induced by glucagon and isoproterenol. The extents of the responses to nor-epinephrine and phenylephrine, however, were decreased markedly in liver perfused with a calcium-free medium and/or with phentolamine. Infusion of calcium into the calcium-deficient liver caused an abrupt elevation of glucose production together with a transient reduction of pyridine nucleotides, and the original extent of the response to norepinephrine was recovered. The data presented provide evidence indicating that stimulation of gluco-neogenesis by norepinephrine is mediated through an α-adrenergic and calcium-dependent mechanism in which redox changes of mitochondrial pyridine nucleotides are involved.