Antihypertensive effect of Eucommia ulmoides Oliv. extracts in spontaneously hypertensive rats

To investigate the antihypertensive fractions of Eucommia ulmoides Oliv. and their underlying mechanisms in spontaneously hypertensive rats (SHRs).

In vivo study, Eucommia ulmoides lignans (EuL) and Eucommia ulmoides iridoids (EuI) were administrated to Sprague-Dawley (SD) rats and SHRs, and their blood pressures were measured. Plasma level of nitric oxide (NO) was measured by colorimetric method, and renin activity (RA) and plasma concentration of angiotensin II (Ang II) were measured by radioimmunoassay. In vitro study, rat mesenteric artery was treated with EuL and the vessel relaxation responses were determined.

EuL could lower blood pressures of both SD rats and SHR dose-dependently by either intravenous (i.v.) or intragastric (i.g.) administration, but EuI failed to affect blood pressure in the two kinds of rats. Meanwhile, no synergistic effect was observed with the combination of EuL and EuI. The plasma level of NO in SHR treated with EuL 300 mg/kg twice a day was markedly increased. Both plasma RA and Ang II level were decreased with long-term oral treatment of EuL 150 and 300 mg/kg twice a day. In perfusion experiment, EuL relaxed mesenteric artery quickly and dose-dependently and the effect on the artery with and without endothelium was the same.

EuL may be the effective fraction to lowering blood pressure and its antihypertensive effect is probably associated with regulating NO and renin-angiotensin system (RAS) and directly relaxing artery.