EFFECTS OF NITRIC-OXIDE INHIBITION ON THE RENAL PAPILLARY BLOOD-FLOW RESPONSE TO SALINE-INDUCED VOLUME EXPANSION IN THE RAT

1. Evidence indicates that nitric oxide (NO) exerts a paracrine influe nce in the renal medulla. Increases in papillary blood flow are though t to be an important determinant of the renal response to extracellula r volume expansion. Therefore, in the present study, we have evaluated the role of NO in mediating papillary blood flow (laser-Doppler flowm etry) and excretory responses to volume expansion with isotonic saline (3% body weight, 15 min). 2. Infusion of the NO synthesis inhibitor N -omega-nitro-L-arginine methyl ester (10 mu g min(-1) kg(-1)), signifi cantly attentuated the renal diuretic and natriuretic responses to vol ume expansion as well as the renal hydrostatic interstitial pressure i ncrease induced by this manoeuvre. The percentages of the water and so dium excreted in Ih by the N-omega-nitro-L-arginine methyl ester-pretr eated animals were 36% and 40% of the load, whereas those of the contr ol animals were 44% and 65%, respectively. 3. In similar experiments p erformed in the exposed papilla of Munich Wistar rats, the same dose o f N-omega-nitro-L-arginine methyl ester reduced basal papillary blood flow and blunted the elevation in papillary blood flow induced by volu me expansion (6% versus 16% in the control animals). 4. These results indicate that the inhibition of NO synthesis blunts the renal excretor y and papillary responses to volume expansion, suggesting that NO modu lates these responses through changes in papillary blood flow and rena l interstitial hydrostatic pressure.