(±)-Synephrine (hydrochloride)

(±)-Synephrine is an alkaloid with vasoconstrictor and metabolic activities.^1,2,3 It binds to α_1A-, α_2A-, and α_2C-adrenergic receptors (ARs; K_is = 78, 36.7, and 24.4 µM, respectively).⁴ (±)-Synephrine is an agonist of α_1A-ARs in HEK293 cells (EC₅₀ = 4 µM in a reporter assay) but not in CHO cells expressing α_2A- or α_2C-AR. It also acts as an antagonist of α_1A-, α_2A-, and α_2C-ARs, inhibiting L-phenylephrine-induced activation of α_1A-AR in HEK293 cells and activation of α_2A- and α_2C-ARs induced by the α₂-AR agonist medetomidine in CHO cells (IC₅₀s = 12.8, 26, and 27.3 µM, respectively, in reporter assays). (±)-Synephrine induces contractions in isolated rabbit aortic rings (EC₅₀ = 6.2 µg/ml) and increases ligation-induced mean arterial pressure in rats when administered at a dose of 2 mg/kg per day.^1,5 It induces lipolysis in isolated rat and human adipocytes when used at concentrations of 100 and 1,000 µg/ml.² (±)-Synephrine (50 µM) increases phosphorylation of Akt and AMP-activated protein kinase (AMPK) and translocation of Glut4 to the plasma membrane, as well as increases insulin-induced glucose consumption in L6 muscle cells when used at concentrations ranging from 25 to 200 µM.³

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1. Huang, Y.-T., Wang, G.-F., Chen, C.-F., et al. Fructus aurantii reduced portal pressure in portal hypertensive rats. Life Sci. 57(22), 2011-2020 (1995).

2. Mercader, J., Wanecq, E., Chen, J., et al. Isopropylnorsynephrine is a stronger lipolytic agent in human adipocytes than synephrine and other amines present in Citrus aurantium. J. Physiol. Biochem. 67(3), 443-452 (2011).

3. Hong, N.-Y., Cui, Z.-G., Kang, H.-K., et al. p-Synephrine stimulates glucose consumption via AMPK in L6 skeletal muscle cells. Biochem. Biophys. Res. Commun. 418(4), 720-724 (2012).

4. Ma, G., Bavadekar, S.A., Schaneberg, B.T., et al. Effects of synephrine and β-phenethylamine on human α-adrenoceptor subtypes. Planta Med. 76(10), 981-986 (2010).

5. Bevan, J.A., and Osher, J.V. Relative sensitivity of some large blood vessels of the rabbit to sympathomimetic amines. J. Pharmacol. Exp. Ther. 150(3), 370-374 (1965).