THE EFFECTS OF A NIGERIAN SPECIE OF VISCUM ALBUM (MISTLETOE) LEAF EXTRACT ON THE BLOOD PRESSURE OF NORMOTENSIVE AND DOCA-INDUCED HYPERTENSIVE RATS.

Fresh leaves from V. album plant was collected and extracted using standard methods. Acute toxicity studies showed that the crude extract had an LD50 value of 417.5 mg/kg. mice, i.p. Based on this value, test doses (5-160mg/kg) below the LD50 value were selected and used to determine the effects of each dose of extract on the arterial blood pressure (BP) and heart rate of normotensive and hypertensive rats. Some pharmacological agents like propranolol, noradrenaline, acetylcholine and atropine sulphate were also used to assess the mechanism of action of the extract on blood pressure. From the results, the extract produced a dose-dependent depression of blood pressure and heart rate in both normo- and hypertensive rats. At doses of 5mg/kg and 160mg/kg, the extracts produced about 8.99 ± 3.2% and 54 ± 7.4% depression of BP respectively, in normotensive rats while the corresponding values for the hypertensives were 4.8 ± 2.3% and 43.9 ± 5.5% respectively. The duration of action of the extract was also found to be dose-dependent. Noradrenaline (1.5 μg/kg) blocked the action of the extract. Both propranolol (1.0μg/kg) and atropine (1.5μg/kg) failed to block or abolish the action of the extract on rat BP. We suggest a non-adrenergic, non-cholinergic mechanism for the action of the extract on blood pressure