Nongyao Kitjaroennirut, Chaweewan Jansakul and Prakart Sawangchote

pp. 281 - 289

Abstract

Rhizome of Tacca integrifolia, a Thai folk medicinal herb, has been used for controlling blood
pressure and improving sexual function in humans. However, the biological activities of this herb on the
cardiovascular system have not yet been documented. In the present study, we investigated the cardiovascular
effects of methanolic extract from the rhizome of this herb (Tacca extract). In the in vivo study, intravenous
injection of the Tacca extract (0.04-40 mg/kg) caused a decrease in both mean arterial blood pressure and
heart rate of anesthetized rats (Nembutal sodium, 60 mg/kg, i.p.) in a dose dependent manner. Pretreatment
of the animals with muscarinic receptor antagonist, atropine (1 mg/kg, i.v.), significantly reduced the hypotensive and the negative chronotropic activities of the Tacca extract.
In the in vitro preparation, the Tacca extract (0.001-3 mg/ml) caused a decrease in both force and rate
of spontaneous contraction of isolated atria in a dose dependent manner. These effects were reduced by preincubation of the atria with atropine (10^-7 or 10^-6 M). For isolated blood vessels, the Tacca extract (0.003-3 mg/
ml) caused vasodilation of endothelium-intact thoracic aortic rings pre-constricted with phenylephrine (3×10^-6 M). This effect disappeared after pre-incubation of blood vessels with atropine (10^-6 M) or with N^ω-nitroL-arginine (3×10^-4 M), or by removing the vascular endothelium.
The results obtained suggest that the hypotensive and negative chronotropic effects of the Tacca
extract in the rat are due to the active components acting via the muscarinic receptors at the blood vessel to
cause vasodilatation by stimulating the release of nitric oxide, as well as on the muscarinic receptors at the
atria to cause the decrease of both rate and force of the atrial contraction.

Keywords

• Tacca integrifolia
• blood pressure
• vasodilation
• nitric oxide
• acetylcholine receptors