Cardiovascular Pharmacology: Open Access

Abstract

Effects of an Extract of Hawthorn on Arterial Blood Pressure in Anaesthetized Rats

Susan WS Leung, Miranda MW Wong and Ricky YK Man

Hawthorn is an herbal medicine that has been used to treat various cardiovascular disorders, including angina, arrhythmias, congestive heart failure and hypertension. Its major components include flavonoids and oligomeric procyanidins. The present study examined the cardiovascular effects of a commercially available hawthorn extract (WS 1442) in anesthetized rats. Male adult Sprague Dawley rats were anesthetized and their carotid arteries were cannulated for blood pressure and heart rate measurement. After bolus intravenous injections of WS 1442 (3.125, 6.25, 12.5 and 25 mg.kg-1), mean arterial blood pressure (104 ± 3 mmHg) was reduced transiently in a dose-dependent manner. A greater effect on the diastolic than on the systolic blood pressure was observed. Heart rate was not significantly affected by all doses of WS 1442. Infusion of WS 1442 (10 and 28 mg.kg-1.min-1 for 7 min) resulted in sustained decreases in mean arterial blood pressure without any significant changes in heart rate.

Twenty minutes after the infusion, mean arterial blood pressure returned to the baseline values. Phenylephrine (1, 3 and 10 μg.kg-1) dose-dependently increased arterial blood pressure and this hypertensive effect in rats with prior exposure to WS 1442 was significantly smaller than in those without. These findings suggest that the hawthorn extract possesses hypotensive action. Pre-exposure to the hawthorn extract also impaired the blood pressure response to phenylephrine. As such, hawthorn may have a modulatory effect on the regulation of blood pressure by the a-adrenergic system.