EFFECTS OF N(G)-NITRO-L-ARGININE ON ISOLATED RABBIT AFFERENT ARTERIOLES

We examined the effects of N(G)-nitro-L-arginine (L-NNA) on isolated r abbit afferent arterioles to confirm that nitric oxide is released at the resistance vessel level in the kidney. We microdissected the super ficial afferent arterioles from the kidneys of New Zealand White rabbi ts. 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 aff erent arterioles in a dose-dependent manner, and acetylcholine increas ed 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 mum in 20 min, but N(G)-nitro-D-argi nine (10(-4) M) did not affect them (from 21.8 +/- 1.3 to 21.8 +/- 1.5 mum). L-Arginine (10(-2) M) restored the lumen diameter of L-NNA-cont racted afferent arterioles to the control levels. These findings indic ate that the isolated afferent arteriole has the ability to release or to synthesize and release nitric oxide under basal conditions and tha t this basal release of nitric oxide plays an important role in the ba sal tone of the afferent arteriole.