Vascular Pharmacological Effect Of Extract From Mulberry Leaves

BACKGROUNDMorus alba L. mainly exists in China, Japan and Korea. In many places of China, especially in Jiangsu and Zhejiang, there are lots of wild or planted Morus alba L, the leaf of which (mulberry leaf, one of the Chinese herb) is ordinarily used to feed silkworms. Mulberry leaf has been reported to have clinical effects on night sweat, insomnia, diabetes, hypertension and so on. Modern pharmacological analysis showed that mulberry leaf contains N-containing-sugars, rutin, quercetin, amino acid, vitamin, microelement and other chemical element. It has been found that quercetin, one of the primary components of mulberry leaf, could induce significant vasorelaxation. In the screening study of vasoactive Chinese herbs, we found that mulberry leaf had significant cardiovascular activity. However, the exact effect of mulberry leaves on vascular system is not been clarified.OBJECTIVESIn this experiment we used the organ bath technique to explore the pharmacological effect and underlying mechanisms of extract from mulberry leaves (EML) on isolated rat thoracic aortas.METHODS1. Organ bath experimentAortic rings isolated from Sprague-Dawley rats were mounted between two stainless steel hooks and suspended in an organ bath containing Krebs-Henseleit solution (K-H solution), and the tension of the aortic rings was recorded in a data acquisition system (MedLab, Nanjing Medease Co. Ltd., China).2. Isolated rat heart constant flow perfusionImmediately after cervical dislocation, the normal male Sprague-Dawley rat hearts were rapidly excised, cannulated via the aorta and perfused retrogradely for 50 min under constant pressure (76 mmHg) with K-H solution in a Langendorff apparatus. Hemodynamic parameters including coronary flow (CF), left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), and left ventricular developed pressure (LVDP) were monitored.RESULTS1. Dose-dependent effect of EML on aortic rings preconstricted by KCl and phenylephrineEML induced vasorelaxation in dose-dependent both in endothelium-intact and -denuded aortas preconstricted by KCl, the EC50 value of EML is 6.2 g/L and 6.0 g/L, respectively. The effect of EML on phenylephrine (PE) preconstricted aortaswas similar as that on KCl preconstricted aortas, and the EC50 value was 6.5 g/L (for endothelium-intact) and 6.4 g/L (for endothelium-denuded), respectively.2. Time-dependent effect of EML on aortic rings preconstricted by KCl and PE The EC50 concentration of EML evoked a time-dependent vasorelaxation in aortas both preconstricted by KCl and PE compared with control group.3. Ca2+-dependent effect of EML on aortic ringsPretreatment with EC50 concentration of EML for 30 min decreased vasoconstriction to CaCl2 compared with control group.4. Effect of EML on aortic rings pretreated with verapamilIn endothelium-denuded aortas pretreated with verapamil for 30 min, a L-type Ca2+ channel inhibitor, and preconstricted by PE subsequently, EML (6.4 g/L) further increased vasoconstriction (P<0.01, vs. control group) instead of vasorelaxation. Such effect of EML was cancelled by ruthenium red, a ryanodine receptor inhibitor, but not by heparin sodium, an IP3 receptor inhibitor. The same effect of EML was obtained in endothelium-denuded aortas.5. Effect of EML on left ventricular functionsPretreatment with EML (50 mg/L) for 15 min increased LVSP, LVDP and CF, but decreased LVDP and HR compared with control group.CONCLUSIONSIn the present study we found that EML has biphasic effects of relaxation and constriction on aortas. The vasorelaxation effect of EML may be mediated byinhibiting voltage-dependent Ca2+ channel and receptor-dependent Ca2+ channel to decrease Ca2+ influx to vascular smooth muscle cells. And the vasoconstriction effect of EML may be via activating ryanodine receptor to release Ca2+ from sarcoplasmic reticulum in vascular smooth muscle cells.