BASAL AND STIMULATED NITRIC-OXIDE IN CONTROL OF KIDNEY-FUNCTION IN THE AGING RAT

To investigate the activity of nitric oxide (NO) in control of renal h emodynamics during aging, studies were conducted on conscious Sprague- Dawley rats aged 3-5 mo (young, Y) and 18-22 mo (old, O). Blood pressu re (BP) and renal vascular resistance (RVR) were higher in O vs. Y in control, and acute systemic NO synthesis inhibition (NOSI) increased B P and RVR, with an enhanced renal vasoconstrictor response in O. Infus ion of the NO substrate L-arginine produced similar, selective renal v asodilation in both groups. The endothelium-dependent vasodilator acet ylcholine caused similar falls in BP and RVR, whereas sodium nitroprus side produced an exaggerated depressor response in O vs. Y without fal ls in RVR in either age group. Urinary excretion of the stable NO oxid ation products (NOx) decreased with age, suggesting a decline in the o verall somatic NO production. In conclusion, basal tonically produced NO has a more pronounced role in maintenance of renal perfusion in agi ng, whereas L-arginine- and agonist-stimulated renal vasodilation is n ot impaired with age. NO production from some source may be reduced wi th aging, as indicated by falls in 24-h NOx excretion, although the si milarity in presser response and enhanced renal vasoconstrictor respon se to NOSI suggests that the role of NO in control of total peripheral and renal vascular resistance is maintained.