Nitric oxide synthase activity and isoforms in rat renal vasculature

Experiments were performed to quantify nitric oxide synthase (NOS) activity and identify the NOS isoforms present in the Sprague-Dawley rat renal vasc ulature. NOS enzymatic activity was measured by adding [H-3]arginine to mic rodissected renal blood vessels and quantifying the conversion to [H-3]citr ulline by reverse-phase high-performance liquid chromatography. Total NOS a ctivity was greatest in microdissected vasa recta (123+/-41 pmol.mg(-1).h(- 1), n=5) and significantly less in glomeruli (46+/-9 pmol.mg(-1).h(-1), n=6 ) and afferent arterioles (42+/-10 pmol.mg(-1).h(-1), n=6) and averaged <5 pmol.mg(-1).h(-1) in arcuate (n=8) and interlobular (n=9) arteries. Additio n of 1.0 nmol/L EDTA to the reaction decreased NOS activity to <5 pmol.mg(- 1).h(-1) in afferent arterioles, glomeruli, and vasa recta (n=5 each), indi cating that the NOS enzymatic activity in these segments is primarily a res ult of constitutive NOS. Both neuronal and endothelial NOS mRNA were identi fied in each vascular segment by reverse transcription-polymerase chain rea ction, but inducible NOS mRNA was detected only in microdissected arcuate a rteries. The present experiments indicate that the vasa recta, glomeruli, a nd afferent arterioles contain large amounts of calcium-dependent NOS enzym atic activity and that neuronal NOS and endothelial NOS mRNA;are present in these segments.