Endothelium-dependent and endothelium-independent vasorelaxant effects of unripe Rubus coreanus Miq. and Dendropanax morbiferus H. Lév. extracts on rat aortic rings

Background: Many clinical trials on antihypertensive drugs have confirmed the usefulness of these drugs in regulating blood pressure effectively. However, all the drugs usually require long-term use; thus, economic burdens as well as some adverse effects, including headache, diarrhea, skin rash, edema, fever, and liver and kidney dysfunction, accompany their use. Therefore, we attempted to identify natural medications for treating hypertension. We investigated the antihypertensive effects of Dendropanax morbiferus H. Lév. extract (DP), enzymatically hydrolyzed DP extract (Hy-DP) and 5% unripe Rubus coreanus Miq. ethanol extract (5-uRCK).

Methods: Extracts of the unripe R. coreanus were made using 20 volumes of 5% ethanol at 100 °C for 4 h. The dried leaves of D. morbiferus were subjected to enzymatic hydrolysis by protease, trypsin, bromelain and papain to increase _L-arginine and GABA levels. Vasorelaxant effects of these extracts were evaluated on rat aorta precontracted with phenylephrine. In addition, hippocampal neurons, RAW 264.7 macrophages and human umbilical vein endothelial cells (HUVECs) were used to exam nitric oxide (NO) production and NO synthase (NOS) gene expression.

Results: DP, Hy-DP and 5-uRCK dose-dependently relaxed isolated rat aortic rings contracted with phenylephrine; however, Hy-DP was more effective than DP. _L-NAME and ODQ differentially inhibited Hy-DP- and 5-uRCK-induced relaxation; both _L-NAME and ODQ completely blocked 5-uRCK-mediated relaxation. Endothelium-denuded aortic ring relaxation was induced much less by 5-uRCK than by Hy-DP. Therefore, 5-uRCK and Hy-DP induced vascular relaxation by endothelium-dependent and partially endothelium-dependent mechanisms, respectively. Hy-DP and 5-uRCK induced eNOS gene expression and NO production in endothelial cells but did not change iNOS/nNOS expression or NO production in macrophages or neuronal cells. Both Hy-DP and 5-uRCK effectively induced vascular relaxation via similar but slightly different mechanisms. The best effective combination was investigated after mixing Hy-DP and 5-uRCK at different ratios. The 2:1 Hy-DP:5-uRCK mixture inhibited ACE, cGMP- and cAMP-dependent phosphodiesterase activity and vascular relaxation better than the other mixtures.

Conclusion: In conclusion, Hy-DP and 5-uRCK exert antihypertensive effects through different endothelium-dependent or endothelium-independent mechanisms. These findings may greatly help elucidate the mechanisms of clinical efficacy of Hy-DP:5-uRCK mixtures used for blood pressure regulation.

Keywords: Dendropanax morbiferus H. Lév.; GABA; Hypertension; L-arginine; Nitric oxide; Unripe Rubus coreanus Miq..