Effects of epinephrine and norepinephrine on lipid mobilization from coho salmon liver incubated in vitro.

Abstract

The direct effects of epinephrine and norepinephrine (NE) on lipid mobilization were studied in coho salmon liver slices incubated in vitro. Fatty acid (FA) release from liver slices was measured continuously by pH-stat titration. The pH-stat assay system was validated by simultaneous colorimetric measurement of FA and glycerol release. Liver slices incubated in a glucose-free, low buffering capacity medium and stimulated with NE (10(-6) M) exhibited a one proton (titrimetric) to one FA (colorimetric) release profile. Under similar conditions, NE administration also stimulated glycerol release, in the expected three FA (colorimetric) to one glycerol (colorimetric) ratio. NE stimulated FA release from liver slices in a dose-dependent manner; epinephrine did not have a lipolytic effect. The beta-agonist isoproterenol stimulated FA release, whereas alpha-agonists had no effect. Furthermore, the beta-antagonist propranolol inhibited both NE- and beta-agonist-stimulated FA release. Liver triacylglycerol lipase activity was also stimulated by NE. Propranolol inhibited NE-stimulated lipase activity. These results establish the presence of hormone-sensitive lipase in salmon liver and suggest that NE-stimulated lipid mobilization in salmon liver is mediated through beta-adrenergic pathways.