Abstract
The fruit extracts of Citrus aurantium (bitter orange) are traditionally used as weight-loss products and as appetite suppressants. A component of these extracts is octopamine, which is an adrenergic agent. Weight-loss and adrenergic actions are always related to metabolic changes and this work was designed to investigate a possible action of octopamine on liver metabolism. The isolated perfused rat liver was used to measure catabolic and anabolic pathways and hemodynamics. Octopamine increased glycogenolysis, glycolysis, oxygen uptake, gluconeogenesis and the portal perfusion pressure. Octopamine also accelerated the oxidation of exogenous fatty acids (octanoate and oleate), as revealed by the increase in 14CO2 production derived from 14C labeled precursors. The changes in glycogenolysis, oxygen uptake and perfusion pressure were almost completely abolished by α1-adrenergic antagonists. The same changes were partly sensitive to the β-adrenergic antagonist propranolol. It can be concluded that octopamine accelerates both catabolic and anabolic processes in the liver via adrenergic stimulation. Acceleration of oxygen uptake under substrate-free perfusion conditions also means acceleration of the oxidation of endogenous fatty acids, which are derived from lipolysis. All these effects are compatible with an overall stimulating effect of octopamine on metabolism, which is compatible with its reported weight-loss effects in experimental animals.
Highlights
Octopamine is produced from tyramine and has been identified as a naturally occurring biogenic amine in invertebrates and vertebrates [1]
In these experiments it was investigated if octopamine is active in hemodynamics, because this kind of action is typical for compounds that act as adrenergic agents [19]
Statistical analysis was performed with the GraphPad Prism software®. Octopamine accelerates both carbohydrate and fatty acid metabolism in the rat liver, an action that is in some aspects similar to that reported for the fat body of insects [7]
Summary
Octopamine is produced from tyramine and has been identified as a naturally occurring biogenic amine in invertebrates and vertebrates [1]. To characterize the metabolic effects of octopamine in the liver was, the main purpose of the present work This was accomplished by measuring several basic metabolic routes in the isolated perfused rat liver, a preparation which preserves the microcirculation and allows the measurement of hemodynamic parameters such as the portal perfusion pressure [18]. The results of this investigation should lead to an increased understanding of the effects of octopamine in mammalian organisms
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