The aim of the present study is to investigate the effect of standardized Phikud Navakot extract (NVKE) on aortic rings from male Sprague Dawley rats. Changes in tension were measured using an isometric force transducer and recorded on the PowerLab recording system. Vasorelaxant effect of NVKE was examined in the presence of indomethacin (10 microM), NG-nitro L-arginine methyl ester (L-NAME, 300 microM), methoxamine (0.1-300 microM), carbachol (1 nanoM-30 microM), or sodium nitroprusside (0.1 nanoM-10 microM). The results showed that NVKE (1-300 microg/mL) caused vasorelaxation in a concentration-dependent manner with a pEC50 value of 4.27 + 0.24 and Rmax of 67.7 + 13.9%. Pretreatment with indomethacin or L-NAME did not affect NVKE-induced vasorelaxation. However, co-incubation of indomethacin and LNAME significantly reduced (p < 0.05) vasorelaxation to NVKE (100 microg/mL). Pre-treatment with NVKE significantly decreased (p < 0.05) endothelium-dependent relaxations to carbachol (Rmax = 52.90 + 14.3%), but not to sodium nitroprusside. Moreover, contractions to methoxamine were unaffected after pretreatment with NVKE. The present study suggested that NVKE decreased vasorelaxation to carbachol in the rat aorta, which may exert at least against muscarinic receptors. These findings support the use of Phikud Navakot, a major ingredient of Yahom Navakot, against dizziness and fainting.

Keywords: Navakot, Aorta, Vasorelaxation, Angelica dahurica, Atractylodes lancea, Ligusticum chuanxiong, Angelica sinensis, Artemisia vulgaris, Saussurea costus, Picrorhiza kurrooa, Terminalia chebula, Nardostachys jatamansi