Reduced hepatic cAMP production in mice homozygous for a deletion of the C/EBPβ gene (–/–). C/EBPβ^–/– and WT control mice were lightly anesthetized, and a liver biopsy was freeze-clamped to measure the basal concentration of cAMP. Glucagon was then delivered through the portal vein at 50 μg/kg. One minute after the glucagon injection, a second piece of liver was biopsied for the determination of cAMP levels. The data are mean ± SEM for seven to eight animals per group. *Significantly reduced compared with WT mice; P < 0.05. WT, wild-type.