Effects of L-arginine and furosemide on blood pressure and renal function in volume-expanded rats

1. The aim of the present study was to investigate the effects of L-arginine (L-Arg) on blood pressure and water and electrolyte excretion in control and extracellular fluid volume-expanded rats (10% bodyweight with 0.9% NaCl) and to determine whether diuretic treatment with furosemide (FUR) can be optimized by the administration of L-Arg in this model. 2. Both groups of animals were anaesthetized, divided into groups and treated with either 7.5 mg/kg FUR, 250 mg/kg L-Arg, 1 mg/kg NG-nitro-L-arginine methyl ester (L-NAME), FUR + L-NAME or FUR + L-Arg. Mean arterial pressure (MAP), diuresis, natriuresis and kaliuresis were determined. 3. Extracellular fluid volume expansion induced no changes in MAP in control and volume-expanded rats (92+/-6 vs 100+/-8 mmHg, respectively). The hypotension induced by FUR in control and volume-expanded rats (69+/-7 and 76+/-5 mmHg, respectively) was significantly (P < 0.01) enhanced by the administration of L-Arg (54+/-3 and 64+/-3 mmHg, respectively). 4. Injection of L-NAME increased MAP and diminished diuresis, natriuresis and kaliuresis in both groups. 5. Furosemide-induced water and electrolyte excretion was blunted by the administration of L-NAME. 6. The combination of L-Arg + FUR increased diuresis induced by FUR alone (control rats: 29.33+/-1.68 vs 12.91+/- 0.41 microL/min per 100 g, respectively; volume-expanded rats: 248.5+/-25.4 vs 112,6+/-8.3 microL/min per 100 g, respectively; P < 0.01). 7. The administration of the combination of L-Arg + FUR promoted a decrease in the sodium/water excretion ratio compared with the administration of FUR alone (control rats: 0.230+/-0.018 vs 0.45+/-0.03, respectively, P < 0.001; volume-expanded rats: 0.091+/-0.010 vs 0.22+/-0.03, respectively, P < 0.01). 8. The potassium/water excretion rate induced by FUR alone and in the presence of L-Arg followed a pattern similar to that seen for natriuresis (control rats: 0.35+/-0.05 vs 0.20+/-0.05 microEq/min per 100 g, respectively; volume-expanded rats: 0.045+/-0.008 vs 0.014+/-0.003 microEq/min per 100 g, respectively; P < 0.01). 9. The decrease in the electrolyte/water excretion ratio observed with FUR + L-Arg in volume-expanded rats was greater than in control animals. 10. The results of the present study show that the administration of FUR with L-Arg contributes to enhanced hypotensive and diuretic effects of FUR, thus diminishing the relative electrolyte excretion in normal conditions and in extracellular fluid volume expansion.