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Crude hydromethanolic extract of Tylophora hirsuta (Th.Cr) was studied in spontaneous hypertensive Wistar rats for possible effects on high blood pressure and heart rate. In the absence of atropine, fall in arterial blood pressure was 64±7 mmHg at the dose of 100 mg/kg while in the presence of atropine, there was no effect on arterial blood pressure suggesting cholinergic receptor blockade. Fall in heart rate, in the absence of atropine, was 218±8 beats per minute (BPM) while, fall in heart rate, in the presence of atropine was 110±5.6 BPM, indicating that the action is through cholinergic muscarinic receptors as atropine is a typical anticholinergic drug. The percent fall in blood pressure and heart rate were standardized versus acetylcholine; standard cholinergic drug. Th.Cr tested mildly positive for alkaloids, flavonoids and strongly positive for terpenes and terpenoids, and saponins. α- Amyrin acetate was isolated from the n-hexane fraction of Th.Cr for the first time from T. hirsuta. The results confirm the presence of acetylcholine like substances in T. hirsuta that provide a basis for its traditional use in treatment of hypertension. The action may be attributed to the phytochemicals like flavonoids, saponins, terpenes and terpenoids and α- amyrin acetate isolated for the first time from the plant.
Key words: Tylophora hirsuta, arterial blood pressure, antihypertensive, α- amyrin acetate.