Oral diuretic activity of hot water infusion of Sri Lankan black tea (Camellia sinensis L.) in rats

BACKGROUND: Black tea [Camellia sinensis (L.) O. Kuntze (family: Theaceae)] has been used by Sri Lankan traditional practitioners to promote diuresis. However, the type and grade of tea is not specified. MATERIALS AND METHODS: This study investigates the diuretic activity of black tea infusion (BTI) in rats using Broken Orange Pekoe Fannings (BOPF) grade from major agroclimatic elevations: high-, mid-, and low-grown. Different concentrations of BTI, furosemide (positive control), and water (vehicle) were orally administered to starved (18 h) male rats (n = 9/group), then hydrated. Acute and chronic (28 days) diuretic activities were assessed by measuring cumulative urine output at hourly intervals for 6 h. Electrolyte levels (Na(+), K(+), Ca(2+), H(+), Cl(−), HCO(3)(−)), pH, osmolarity of urine, and glomerular filtration rate (GFR) of treated rats were determined. RESULTS: Administration of BTI induced a significant (P < 0.05) and dose-dependent diuretic activity, which varied with the tea produced in different agroclimatic elevations. Diuretic activity had a rapid onset (1(st) h), peaked at 2(nd) h and maintained up to 4(th) h (except the low dose). Furthermore, there was a dose-dependent increase in micturition frequency, which peaked at 2(nd) h. A close association between the caffeine content of tea and diuretic activity was evident. BTI-induced diuresis was accompanied with an increased urine Na(+) level and GFR. The diuretic activity of BTI was mediated via multiple mechanisms: inhibition of both aldosterone secretion (with increased Na(+)/K(+) ratio) and carbonic anhydrase [with decreased Cl(−)/(Na(+) + K(+)) ratio] and via thiazide type of diuretic action (evaluated with increased Na(+)/Cl(−) ratio). CONCLUSION: The Sri Lankan BOPF grade black tea possesses mild oral diuretic activity whose efficacy differs with the agroclimatic elevation of production. Furthermore, it supports the traditional claim that the black tea acts as a diuretic.