Hypoglycaemic and hypotensive effects of Globimetula cupulata (DC) Van Tieghem (Loranthaceae) aqueous leaf extract in rats.

The leaves of some mistletoes, specifically Loranthus micranthus Linn, Tapinanthus dodoneifolius (DC) Danser and Globimetula cupulata (DC) Van Tieghem (family: Loranthaceae), are used traditionally in Nigerian folk medicine to manage, control and/or treat a plethora of human ailments, including diabetes mellitus and hypertension. In order to scientifically appraise some of the folkloric, ethnomedical uses of Globimetula species, the present study was undertaken to investigate the hypoglycaemic and hypotensive effects of Globimetula cupulata aqueous leaf extract (GCE, 50-800 mg/kg po) in rat experimental paradigms. The hypoglycaemic effect of the plant extract was examined in normal (normoglycaemic) and diabetic (hyperglycaemic) rats using a streptozotocin (STZ)-induced diabetes model. Normotensive Wistar and hypertensive Dahl salt-sensitive rats were used to investigate the hypotensive (antihypertensive) effect of the plant extract. Metformin (MFM, 500 mg/kg po) was used as the reference hypoglycaemic agent for comparison. Acute oral administrations of G cupulata aqueous leaf extract (GCE, 50-800 mg/kg po) caused dose-related, significant (p < 0.05-0.001) hypoglycaemia in normal and STZ-treated diabetic rats. Furthermore, acute intravenous administrations of GCE (50-800 mg/kg iv) produced dose-dependent, significant reductions (p < 0.05-0.001) in systemic arterial blood pressure and heart rates of the normotensive and hypertensive rats used. Although the exact hypoglycaemic and hypotensive mechanisms of action of the plant extract still remain speculative, it is unlikely that the extract induced hypotension in the mammalian experimental animal model via cholinergic mechanisms, since its cardiovascular effects were resistant to atropine pretreatment. However, the findings of this experimental study indicated that Globimetula cupulata aqueous leaf extract possesses hypoglycaemic and hypotensive properties. This therefore lends pharmacological support to the folkloric, ethnomedical uses of the plant in the management and/ or control of diabetes mellitus and hypertension among the Yoruba-speaking people of western Nigeria.