Hypoglycaemic and hypotensive effects of Psidium gajava Linn. (Myrtaceae) leaf aqueous extract

The leaf of Psidium guajava Linn. (family, Myrtaceae) is used traditionally in African 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 anecdotal, folkloric, ethnomedical uses of P. guajava Linn., the present study was undertaken to investigate the hypoglycemic and hypotensive effects of P. guajava leaf aqueous extract (PGE, 50-800 mg/kg) in rat experimental paradigms. The hypoglycemic effect of the plant's extract was examined in normal and diabetic rats, using streptozotocin (STZ)-induced diabetes mellitus model. Hypertensive Dahl salt-sensitive rats were used to investigate the hypotensive (antihypertensive) effect of the plant's extract. Chlorpropamide (CPP; 250 mg/kg, p.o.) was used as the reference hypoglycemic agent for comparison. Acute oral administrations of the plant's extract (PGE; 50-800 mg/kg, p.o.) caused dose-related, significant (p < 0.05-0.001) hypoglycemia in normal (normoglycemic) and STZ-treated, diabetic rats. Moreover, acute intravenous administrations of the plant's extract (PGE, 50-800 mg/kg i.v.) produced dose-dependent, significant reductions (p < 0.05-0.001) in systemic arterial blood pressures and heart rates of hypertensive, Dahl salt-sensitive rats. Although the exact mechanisms of action of the plant's extract still remain speculative at present, it is unlikely that the extract causes hypotension in the mammalian experimental animal model used via cholinergic mechanisms, since its cardiodepressant effects are resistant to atropine pretreatment. The numerous tannins, polyphenolic compounds, flavonoids, pentacyclic triterpenoids, guiajaverin, quercetin, and other chemical compounds present in the plant are speculated to account for the observed hypoglycemic and hypotensive effects of the plant's leaf extract. However, the results of this experimental animal study indicate that the leaf aqueous extract of P. guajava possesses hypoglycemic and hypotensive properties, and thus lend pharmacological credence to the suggested folkloric, ethnomedical uses of the plant in the management or control of adult-onset, type 2 diabetes mellitus and hypertension in some rural African communities.