Evaluation of the Possible Mechanisms of Antihypertensive Activity of Loranthus micranthus: An African Mistletoe

Loranthus micranthus (LM), also called African mistletoe is a major Nigerian Loranthaceae plant used traditionally to treat hypertension. The methanolic leaf extract of the plant (LMME) has been shown to elicit anti-hypertensive activity in rats but mechanism remains unclear. This study was undertaken to study the effect of LM on pressor-induced contraction of rat aorta smooth muscles and serum lipid profiles in mice. The LMME was partitioned to produce n-butanol (NBF-LMME), chloroform (CF-LMME), ethyl acetate (EAF-LMME) and water (WF-LMME) fractions. The median effective concentrations and maximum relaxation of the fractions were determined against epinephrine and KCl pre-contracted rat aorta ring model. Serum lipid profiles and nitric oxide (NO) were determined spectrophotometrically in mice administered per orally 250 mg/kg b.w. of each fraction for 21 days. Data were analyzed statistically. NBF-LMME elicited the highest dose-dependent inhibitory effect on rat aorta pre-contracted with norepinephrine and KCl, followed in decreasing order by WF-LMME > CF-LMME > EAF-LMME. Similar order of activity was observed in the ability of these fractions to inhibit elevation in artherogenic lipids, raise serum nitric oxide and reduce cardiac arginase in mice. We conclude the anti-hypertensive activity of L. micranthus involve anti-artherogenic events, vasorelaxation, cardiac arginase reduction and NO elevation.