Effects of Ya-hom on blood pressure in rats

The effects of Ya-hom, a traditional Thai herbal formulation, on blood pressure were evaluated to verify its use for fainting treatment. Ya-hom has several recipes, which are composed of different medicinal plants in varying ratio. We have selected the most popular commercial preparation to determine the effect on the blood pressure in rats. The water extract of Ya-hom at doses of 0.2, 0.4, 0.6 and 0.8 g/kg initially transiently decreased pressure and over time, increased blood pressure. The duration of the Ya-hom effect on decreasing and increasing blood pressure was dose dependent. The time to maximal effect of Ya-hom on increasing blood pressure was also dose dependent. Phentolamine attenuated the blood pressure decreasing effect but did not affect the blood pressure increasing effect of Ya-hom. Ya-hom was previously shown to increase aortic ring contraction, which was partially inhibited by phentolamine, and increased atrial contraction. It is possible that phentolamine inhibits the effect of Ya-hom on vascular smooth muscle contraction resulting in a prominent positive inotropic effect. This may be the same reason that phentolamine does not influence the effect of Ya-hom on increasing blood pressure. The dominant effect of Ya-hom on increasing blood pressure supports the use of Ya-hom for the treatment of fainting.