MECHANISMS OF CARDIOVASCULAR ACTIVITY OF ANDROGRAPHIS-PANICULATA IN THE ANESTHETIZED RAT

The cardiovascular activities of crude water extract (WE) of Andrograp his 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 ana esthetized Sprague-Dawley (SD) rats for the very first time. FA and an drographolide, which possesses multiple pharmacological activities, el icited no drop in mean arterial blood pressure (MAP), while WE, FB and FC produced a significant fall in MAP in a dose-dependent manner with out 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 t he hypotensive substance(s) of the crude water extract was concentrate d in FB. Pharmacological antagonist studies were consequently only tes ted in FB (5 mg/kg). The hypotensive action of FB was not mediated thr ough effects on the beta-adrenoceptor, muscarinic cholinergic receptor and angiotensin-converting enzyme, for it was not affected by propran olol, atropine and captopril, respectively. However, it seems to work via alpha-adrenoceptors, autonomic ganglion and histaminergic receptor s, since the hypotensive effect of FB was negated or attenuated in the presence of phentolamine, hexamethonium as well as pyrilamine and cim etidine. (C) 1997 Elsevier Science Ireland Ltd.