Abstract
Bitter orange (Citrus aurantium) extract and its primary protoalkaloid p-synephrine are used widely in weight loss/weight management and sports performance products. Because of structural similarities, the pharmacological effects of p-synephrine are widely assumed to be similar to those of ephedrine, m-synephrine (phenylephrine), and endogenous amine neurotransmitters as norepinephrine and epinephrine. However, small structural changes result in the receptor binding characteristics of these amines that are markedly different, providing a plausible explanation for the paucity of adverse effects associated with the wide-spread consumption of p-synephrine in the form of dietary supplements as well as in various Citrus foods and juices. This paper summarizes the adrenoreceptor binding characteristics of p-synephrine relative to m-synephrine, norepinephrine, and other amines as related to the observed pharmacological effects.
Highlights
Bitter orange (Citrus aurantium) extract and its primary protoalkaloid p-synephrine are used widely in weight loss/weight management and sports performance products
Small structural changes result in the receptor binding characteristics of these amines that are markedly different, providing a plausible explanation for the paucity of adverse effects associated with the widespread consumption of p-synephrine in the form of dietary supplements as well as in various Citrus foods and juices
Various articles refer to the potential cardiovascular hazards that may occur as the result of using dietary supplements containing p-synephrine and bitter orange extract [19,20,21,22,23,24], with reference being made to clinical case reports that involve multiherbal and polyalkaloidal and poly-protoalkaloidal products [16, 17]
Summary
Vasoconstriction is produced when ligands acting as agonists bind to α-adrenoreceptors, cardiovascular contractility and increased heart rate occur in response to β1 adrenoreceptor binding, while bronchodilation occurs in response to β-2 adrenoreceptor binding [24]. A reduction in body weight gain was observed at all doses, while no effects were observed on organ weights, biochemical parameters, blood pressure, or heart rate in the treated mice relative to controls Both doses of p-synephrine and the high dose of the bitter orange extract increased hepatic-reduced glutathione, while bitter orange extract decreased lipid peroxidation, and p-synephrine increased the antioxidant enzyme catalase by 6-fold. Structural differences and the resultant altered receptor-binding affinities explain the markedly differing pharmacological responses to similar concentrations and doses of p-synephrine relative to ephedrine, norepinephrine, and other biogenic amines
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