Role of nitric oxide in hypodipsia of rats with obstructive cholestasis

Abstract

Cholestasis is associated with the overproduction of nitric oxide (NO), and NO acts as an inhibitory mechanism when thirst is stimulated by water deprivation or by angiotensin II. Due to the presence of hypodipsia in the cholestatic condition, we have compared the rate of water intake between bile duct-ligated (cholestatic) and sham-operated rats. We have evaluated the effect of NO synthesis inhibition by NG-nitro-L-arginine (L-NNA, 10 mg kg−1/day) on the rate of water intake in cholestatic rats. The results showed that plasma alkaline phosphatase activity (a marker of liver damage) increased after bile-duct ligation, and that its elevation was partially (but significantly) prevented by treatment with L-arginine. A two-week bile-duct obstruction induced a significant decrease in the rate of water intake compared with sham-operated animals (35.87 ± 1.45 vs 42.37 ± 1.99 mL/day, P < 0.05). This effect was corrected by the daily administration of L-NNA. Surprisingly, L-arginine (200 mg kg−1/day) showed similar activity as L-NNA in cholestatic rats and increased water intake, but not in control animals. Systemic NO synthesis inhibition corrected the decrease in water intake observed in cholestatic rats. This suggests an important role for NO in the pathophysiology of hypodipsia in cholestatic subjects. The effect of chronic L-arginine administration observed in cholestatic rats but not seen in the control rats could be explained theoretically by the amelioration of cholestasis-induced liver damage by chronic L-arginine administration in bile duct-ligated rats.