Changes of the Plasma Endothelin in Adaptation to Increased Salt Intake in Rats

OBJECTIVES: Roles for vascular endothelial hormones in body fluid balance have been variously suggested. The present study was aimed at investigating whether the plasma endothelin is altered in responses to acute and chronic perturbations in body fluid balance. METHODS: Effects of intravenous infusion of N(G)-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of endothelium-derived nitric oxide (NO) synthesis, on urinary excretion, blood pressure and plasma levels of endothelin were examined in rats kept on either normal or high-salt diet for two weeks. The plasma endothelin levels in response to an acute extracellular volume expansion (VE) were also determined in normal and 2-kidney, 1 clip (2K1C) hypertensive rats. RESULTS: L-NAME (20 and 200μg · kg(−1) per min) elicited diuretic and natriuretic effects in association with increased blood pressure both in normal and high-salt rats. In high-salt rats, however, the urinary response to L-NAME was attenuated and the pressor response was augmented compared with the control. High-salt intake per se caused a small, but significant, increase of the plasma endothelin. L-NAME(200μg · kg(−1) per min) markedly increased the plasma endothelin, which was not, however, affected by high-salt intake. The plasma endothelin was also marginally increased following VE, the magnitude of which did not differ between the normal and 2K1C rats. CONCLUSION: These results suggest that the endothelin system takes part in adaptation to increased salt-intake. Another evidence indicating a negative modulation of NO on the release of endothelin is also provided.