Nitric oxide-mediated endothelium-dependent relaxation of rat thoracic aorta induced by aqueous extract of red rice fermented with Monascus ruber

Vasodilatory effects of aqueous extract of red rice fermented with Monascus ruber IFO32318 were examined on the isolated rat aorta. The water phase of fermented rice with Monascus (WP/FRM, 0.1-10 mg/ml) caused a transient rel axation of the endothelium-intact rat aorta precontracted with norepinephri ne (NE, 300 nM). The WP/FRM-induced relaxation was abolished by removal of endothelium or in the presence of NG-nitro-L-arginine (L-NNA, 10 I-IM), a n itric oxide (NO) synthase inhibitor. Neither atropine, a muscarinic recepto r antagonist (10 mu M), nor indomethacin, a cyclooxygenase inhibitor (10 mu M), altered the WP/FRM-induced endothelium-dependent relaxation. gamma-Ami nobutyric acid (GABA), one of the principle components of the extract, did not affect the muscle tension of the aorta with intact endothelium. In addi tion, WP/FRM increased the production of NO in primary cultured endothelial cells from human umbilical vein. The enhanced production of NO by WP/FRM w as diminished by pretreatment with L-NNA (10 mu M). In conclusion, WP/FRM i nduces relaxation of rat aorta by releasing NO from endothelium. There seem to be some unknown factor(s) other than acetylcholine (Ach) and GABA, in t he aqueous extract of red rice, which stimulate vascular endothelial cells to produce and/or release NO leading to endothelium-dependent relaxation by WP/FRM. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.