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.