Effects of NG-nitro-L-arginine on isolated rabbit afferent arterioles

We examined the effects of NG-nitro-L-arginine (L-NNA) on isolated rabbit afferent arterioles to confirm that nitric oxide is released at the resistance vessel level in the kidney. We microdissected the superficial afferent arterioles from the kidneys of New Zealand White rabbits. Each afferent arteriole was cannulated with a micropipette system, and the intraluminal pressure was set at 80 mmHg. By our methods, we found that norepinephrine (NE) decreased the lumen diameter of the afferent arterioles in a dose-dependent manner, and acetylcholine increased the lumen diameter of NE-constricted afferent arterioles. L-NNA (10(-4) M) gradually decreased the lumen diameter of afferent arterioles from 21.5 +/- 0.9 to 18.6 +/- 0.9 microns in 20 min, but NG-nitro-D-arginine (10(-4) M) did not affect them (from 21.8 +/- 1.3 to 21.8 +/- 1.5 microns). L-Arginine (10(-2) M) restored the lumen diameter of L-NNA-contracted afferent arterioles to the control levels. These findings indicate that the isolated afferent arteriole has the ability to release or to synthesize and release nitric oxide under basal conditions and that this basal release of nitric oxide plays an important role in the basal tone of the afferent arteriole.