Abstract
The fruit extracts of Citrus aurantium (bitter orange) are traditionally used as weight-loss products and as appetite supressants. An important fruit component is p-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 C. aurantium extract on liver metabolism. The isolated perfused rat liver was used to measure catabolic and anabolic pathways, including oxygen uptake and perfusion pressure. The C. aurantium extract and p-synephrine increased glycogenolysis, glycolysis, oxygen uptake and perfusion pressure. These changes were partly sensitive to α- and β-adrenergic antagonists. p-Synephrine (200 μM) produced an increase in glucose output that was only 15% smaller than the increment caused by the extract containing 196 μM p-synephrine. At low concentrations the C. aurantium extract tended to increase gluconeogenesis, but at high concentrations it was inhibitory, opposite to what happened with p-synephrine. The action of the C. aurantium extract on liver metabolism is similar to the well known actions of adrenergic agents and can be partly attributed to its content in p-synephrine. Many of these actions are catabolic and compatible with the weight-loss effects usually attributed to C. aurantium.
Highlights
Citrus aurantium (Rutaceae) is popularly known as “bitter orange” and its fruit extracts are being marketed and traditionally used as herbal weight-loss products and as appetite suppressants, in Traditional Chinese Medicine they are prescribed in concert with other support herbs [1,2,3,4]
It has been shown that extracts increase lipolysis, thermogenesis and weight loss in both animal models and humans, but always tested in combination with other compounds, especially caffeine, which is known to enhance the thermogenic properties of herbal weight-loss preparations [2,11]
The first experiments were planned in order to test the possible effects of C. aurantium on glycogen catabolism and glycolysis
Summary
Citrus aurantium (Rutaceae) is popularly known as “bitter orange” and its fruit extracts are being marketed and traditionally used as herbal weight-loss products and as appetite suppressants, in Traditional Chinese Medicine they are prescribed in concert with other support herbs [1,2,3,4]. The alkaloids of C. aurantium are structurally related to the adrenergic amines ephedrine (Ephedra sinica), epinephrine, norepinephrine and m-synephrine (Figure 1). The latter is a vasoactive isomer of p-synephrine whose presence in C. aurantium has been suggested, but not confirmed [12,13]. C. aurantium extracts marketed for weight-loss are prepared from dried fruit peels and may be associated with other compounds, mainly caffeine [16]. It has been shown that extracts increase lipolysis, thermogenesis and weight loss in both animal models and humans, but always tested in combination with other compounds, especially caffeine, which is known to enhance the thermogenic properties of herbal weight-loss preparations [2,11].
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