Diuretic activities of a methanolic petal extract and fractions of Hibiscus sabdariffa

Following our earlier work verifying the folkloric diuretic claim of Hibiscus sabdariffa [1], the pharmacological bases for the activity were investigated in 50 saline-loaded albino rats (100–150g; n=5). A whole methanolic extract (WME) of the dried and pulverized petals was prepared by exhaustive cold maceration, and, upon lethal toxicity testing, was found to be safe (LD₅₀>5,000mg/kg i.p.). The WME was then fractionated to yield an n-butanol-soluble fraction (BSF), an ethanol-soluble fraction (ESF), a methanol-soluble fraction (MSF), and a water-soluble fraction (WSF). The WME and its fractions were screened for phytochemical constituents using standard techniques. A comparative metabolic assay was then carried out for the WME and its fractions at the pre-determined dose-level of 40mg/kg i.p. Normal saline (1ml) was used as negative control, while furosemide 3mg/kg, hydrochlorothiazide 10mg/kg, mannitol 200mg/kg, and spironolactone 3mg/kg served as positive controls. Urine output, pH and electrolyte (Na⁺, K⁺, Cl^- and HCO₃ ^-) composition were determined for each animal, and group means±SEM were calculated and tested for statistical significance relative to control groups using the One-Way ANOVA test. The WSF was found to be a significantly (p<0.05) better diuretic than either the WME or any of its other fractions. This is attributable to its high flavonoid content. Its diuretic actions were not significantly (p<0.05) different from those of furosemide 3mg/kg, suggesting a similar mechanism of action.

References: 1. Aguwa, C. N. et al. (2004) Nig. J. Pharm. Res. 3:1–8.