Effect of crude aqueous leaf extract of Viscum album   (mistletoe) in hypertensive rats

Objectives: To study the effect of the crude aqueous extract from Viscum album (mistletoe) leaves on arterial blood pressure (BP) and heart rate (HR) in albino Wistar rats under pentobarbitone anesthesia. Materials and Methods: About 42 male rats (130-150 g) were randomly divided into three batches, as normotensives (NMT, n=18), renal artery-occluded hypertensives, (ROH, n=12), salt-induced hypertensives, (SIH, n=12), The normotensives were further divided into three groups, untreated (control), sham-operated and extract-treated subgroups (n=6 per subgroup) while the ROH and SIH groups were also divided into the treated and untreated subgroups of six rats each. The extract (150 mg/kg) was administered via the oral route, once daily for six weeks. Propranolol (0.5 mg/kg i.v.), atropine (1.5 mg/kg i.v.) and noradrenaline (1.0 mg/kg i.v.) were also administered to elucidate the probable mechanism of action of the extract. Results: The results showed that the control MAP and HR in the normotensives were 97.50±3.20 mmHg and 440.00±12.60 beats/min, respectively. The crude extract produced a significant decrease in BP i.e., 11.28, 23.98 and 18.80% in the NMT, ROH and SIH treated subgroups. The depression produced by the extract on the corresponding HR was not significant in the normotensive, ROH or SIH subgroups. Propranolol blocked the action of the extract on BP. However, atropine did not prevent the extract-induced depression of BP. The extract blocked noradrenaline-induced increase in BP in the NMT. Conclusion: Our data suggest that the mistletoe extract produces antihypertensive effect without alteration in HR, possibly involving sympathetic mechanism.