ALTERED RENAL VASCULAR-RESPONSES IN THE AGING RAT-KIDNEY

Age-related renal functional changes may relate to alterations in the responsiveness to vasoconstrictors and vasodilators. Blood pressure an d renal responses to angiotensin II (ANG II), endothelin-1 (ET), NG-ni tro-L-arginine methyl ester (L-NAME), and to the ANG II receptor antag onist losartan were compared in young (3-mo-old) and older (15-mo-old) male rats. Baseline mean arterial pressure (MAP) values were slightly lower in the older rats, and glomerular filtration rate (GFR) and ren al plasma flow (RPF) were higher. ANG II and ET induced comparable pre sser responses in both groups but produced greater GFR and RPF reducti ons in the older rats. In contrast, the MAP, GFR, and RPF responses to L-NAME were exaggerated in aging rats. Losartan induced modest MAP re ductions in both groups, and comparable renal vasodilatory responses. Thus the aging kidney exhibits exaggerated responses to systemic vasoc onstrictor stimuli, whereas responsiveness to ANG II blockade is prese rved but not enhanced. Whether or not this balance is further impaired later in the aging process remains to be determined.