AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 2 317-R323, Copyright © 1995 by American Physiological Society
Role of renal medullary blood flow in the development of L-NAME hypertension in rats
K. Nakanishi, D. L. Mattson and A. W. Cowley Jr
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226.
The effect of chronic intravenous infusion of the nitric oxide inhibitor
NG-nitro-L-arginine methyl ester (L-NAME; 8.6 mg.kg-1.day-1) on blood
pressure, intrarenal blood flow distribution, and sodium and water balance
was studied in conscious rats. On the 1st day of intravenous L-NAME
infusion, renal medullary blood flow was reduced by 22%, renal cortical
blood flow was unaltered, approximately 1 meq of sodium and 12 ml of water
were retained, and blood pressure increased from 96 +/- 2 to 118 +/- 2
mmHg. Medullary blood flow was maintained at this decreased level, sodium
continued to be retained, body weight continued to increase, and blood
pressure remained elevated for the 5 days of L-NAME infusion. During the
postcontrol period, blood flow in the renal medulla returned to levels not
significantly different from control; the animals went into negative sodium
balance and stopped gaining weight, and blood pressure returned to control.
The present experiments indicate that decreased renal medullary blood flow
and retention of sodium and water play an important role in the development
of hypertension during chronic systemic L-NAME administration despite no
measurable changes in renal cortical blood flow.
