Zea mays L. extracts modify glomerular function and potassium urinary excretion in conscious rats

Diuretic and uricosuric properties have traditionally been attributed to corn silk, stigma/style of Zea mays L. Although the diuretic effect was confirmed, studies of the plant's effects on renal function or solute excretion were lacking. Thus, we studied the effects of corn silk aqueous extract on the urinary excretion of water, Na+, K+, and uric acid. Glomerular and proximal tubular function and Na+ tubular handling were also studied. Conscious, unrestrained adult male rats were housed in individual metabolic cages (IMC) with continuous urine collection for 5 and 3h, following two protocols. The effects of 25, 50, 200, 350, and 500 mg/kg body wt. corn silk extract on urine volume plus Na+ and K+ excretions were studied in water-loaded conscious rats (2.5ml/100g body wt.) in the IMC for 5h (Protocol 1). Kaliuresis was observed with doses of 350 (100.42 +/- 22.32-120.28 +/- 19.70 mu Eq/5h/100g body wt.; n = 13) and 500 mg/kg body wt. (94.97 +/- 29.30-134.32 +/- 39.98 mu Eq/5 h/100 g body wt.; n = 12; p < 0.01), and the latter dose resulted in diuresis as well (1.98 +/- 0.44-2.41 +/- 0.41 ml/5h/100g body wt.; n = 12;p < 0.05). The effects of a 500mg/kg body wt. dose of corn silk extract on urine volume, Na+, K+ and uric acid excretions, and glomerular and proximal tubular function, were measured respectively by creatinine (Cl-cr) and Li + (CILi) clearances and Na+ tubular handling, in water-loaded rats (5 ml/ 100 g body wt.) in the IMC for 3 h (Protocol 2). Cl-cr, (294.6 +/- 73.2, n = 12, to 241.7 +/- 48.0 mu l/ min/100 g body wt.; n = 13; p < 0.05) and the Na+ filtered load (41.9 +/- 10.3, n = 12, to 34.3 +/- .8, n = 13, p < 0.05) decreased and CILi and Na+ excretion were unchanged, while K+ excretion (0.1044 +/- 0.0458, n = 12, to 0.2289 +/- 0.0583 mu Eq/min/ 100 body wt.; n = 13; p < 0.001) increased. For Na+ tubular handling, the fractional proximal tubular reabsorption (91.5 +/- 3.5, n = 12, to 87.5 +/- 3.4%; n = 13; p < 0.01) decreased, and both fractional distal reabsorptions - I and II - increased (96.5 +/- 1.5, n = 12, to 97.8 +/- 0.9%; n = 13; p < 0.01; and 8.2 +/- 3.5, n = 12, to 12.2 +/- 3.4 %, n = 13, p < 0.01, respectively). To summarize, in water-loaded conscious rats (2.5 ml/ 100 body wt.), corn silk aqueous extract is diuretic at a dose of 500 mg/kg body wt. and kaliuretic at doses of 350 and 500 mg/kg body wt. In water-loaded conscious rats (5.0ml/100g body wt.), corn silk aqueous extract is kaliuretic at a dose of 500mg/kg body wt., but glomerular filtration and filtered load decrease without affecting proximal tubular function, Na+, or uric acid excretion. (c) 2005 Elsevier GmbH. All rights reserved.