Renal cortical nitric oxide synthase activity during maturational growth in the rat

The present study was designed to test the hypothesis that growth from puberty to adulthood in the rat is associated with an increase in renal cortical nitric oxide synthase (NOS) activity that results in an augmented impact of nitric oxide (NO) on hemodynamic function. Two groups of male Sprague-Dawley rats were studied: juvenile rats (~2 months old) and mature rats (~5 months old). NOS activity, measured as $N^\omega$ -nitro-L-arginine (NNA)-sensitive ³H-L-citrulline production from ³H-L-arginine, was significantly higher in the renal cortex of mature rats (57±2 pmol/h per mg protein) than in juveniles (42±3 pmol/h per mg protein). Additional animals from each group were anesthetized to determine the acute impact of NOS inhibition on arterial pressure and renal cortical blood flow, measured by single-fiber Doppler flowmetry. Cortical blood flow was higher in mature rats than in juveniles, averaging 22±2 and 16±1 perfusion units, respectively. NOS inhibition (10 mg/kg NNA i.v.) decreased renal cortical blood flow in mature rats by 35±7%, but only by 9±4% in juvenile animals. These data support the hypothesis that maturational growth in the rat is associated with augmented NOS activity coupled with an increased tonic influence of NO on renal cortical blood flow.