Role of l-arginine uptake mechanisms in renal blood flow responses to angiotensin II in rats

Aim: To examine whether reduced renal arginine transport increases the responsiveness of the renal circulation to angiotensin II in salt sensitivity, renal perfusion responses to angiotensin II were examined in the presence of l-arginine transport inhibitor, l-lysine and subsequent l-arginine in Sprague Dawley (SD) and Dahl salt-sensitive (Dahl S) rats. Methods: Laser Doppler probes and a transonic flow probe were used to measure regional renal perfusion and total renal perfusion respectively. Renal perfusion responses to intravenous (i.v.) angiotensin II were sequentially examined under control conditions and during i.v. infusion of l-lysine, l-arginine or nitric oxide synthase inhibitor, N ^G-nitro-l-arginine. Results: Angiotensin II (10 and 100ngkg ^-1min ^-1, i.v.) reduced total renal (-10±3 and -36±5%) and cortical (-10±2 and -28±4%) but not medullary perfusion in SD rats. In these rats l-lysine enhanced the renal perfusion response (P=0.003), whereas subsequent l-arginine reversed this effect (P=0.04). Angiotensin II reduced total renal, cortical and medullary perfusion in Dahl S rats. In Dahl S rats fed high salt, l-lysine did not affect renal perfusion responses to angiotensin II, but subsequent l-arginine blunted the renal blood flow response (P=0.01) and increased the medullary perfusion during angiotensin II infusion (P=0.006). Conclusion: Intact renal l-arginine transport attenuates the vasoconstrictor effects of circulating angiotensin II in the renal cortex in SD rats. l-arginine also plays an important role in protecting the renal medullary circulation from the ischemic effects of angiotensin II in Dahl S rats.