Effects of <em>Citrus aurantium</em> (Bitter Orange) Fruit Extracts and <em>p</em>-Synephrine on Metabolic Fluxes in the Rat Liver

Abstract

The fruit extracts<strong> </strong>of<strong> </strong><em>Citrus aurantium</em> (bitter orange) are traditionally used as weight-loss products and as appetite supressants. An important fruit component is <em>p</em>-synephrine, which is structurally similar to the adrenergic agents. Weight-loss and adrenergic actions are always related to metabolic changes and this work was designed to investigate a possible action of the <em>C. aurantium</em> extract on liver metabolism. The isolated perfused rat liver was used to measure catabolic and anabolic pathways, including oxygen uptake and perfusion pressure. The <em>C. aurantium</em> extract and <em>p</em>-synephrine increased glycogenolysis, glycolysis, oxygen uptake and perfusion pressure. These changes were partly sensitive to a- and b-adrenergic antagonists. <em>p</em>-Synephrine (200 mM) produced an increase in glucose output that was only 15% smaller than the increment caused by the extract containing 196 mM <em>p</em>-synephrine. At low concentrations the <em>C. aurantium</em> extract tended to increase gluconeogenesis, but at high concentrations it was inhibitory, opposite to what happened with <em>p</em>-synephrine. The action of the <em>C. aurantium</em> extract on liver metabolism is similar to the well known actions of adrenergic agents and can be partly attributed to its content in <em>p</em>-synephrine. Many of these actions are catabolic and compatible with the weight-loss effects usually attributed to <em>C. aurantium</em>.

Keywords

• adrenergic signaling
• respiration
• glycogenolysis
• glycolysis
• weight loss