The cardiovascular activities of crude water extract (WE)
of Andrographis paniculata (Burm. f.) Nees (Acanthaceae), its three semi-purified ethyl acetate
(FA), n-butanol (FB) and aqueous (FC) fractions, as well as andrographolide, a major plant
constituent, were elucidated in anaesthetized Sprague-Dawley (SD) rats for the very first time.
FA and andrographolide, which possesses multiple pharmacological activities, elicited no drop in
mean arterial blood pressure (MAP), while WE, FB and FC produced a significant fall in MAP in a
dose-dependent manner without significant decrease in heart rate. The ED50 values for WE, FB and
FC were 11.4, 5.0 and 8.6 mg/kg, respectively. These suggested that the hypotensive substance(s)
of the crude water extract was concentrated in FB. Pharmacological antagonist studies were
consequently only tested in FB (5 mg/kg). The hypotensive action of FB was not mediated through
effects on the beta-adrenoceptor, muscarinic cholinergic receptor and angiotensin-converting
enzyme, for it was not affected by propranolol, atropine and captopril, respectively. However, it
seems to work via alpha-adrenoceptors, autonomic ganglion and histaminergic receptors, since the
hypotensive effect of FB was negated or attenuated in the presence of phentolamine, hexamethonium
as well as pyrilamine and cimetidine. (C) 1997 Elsevier Science Ireland Ltd.