[Role of nitric oxide in the NKCC2 hyperactivity of Dahl "salt-sensitive" rats].
Renal NaCl reabsorption is increased in Dahl "salt-sensitive" (DS) rats, due to an increased activity of the Na-K-Cl cotransporter NKCC2. On the other hand, nitric oxide (NO) is an inhibitor of NKCC2 and a deficient nitric oxide synthase (NOS) seems to play an important role in salt-sensitivity of DS rats. Here, we investigated the hypothesis that NKCC2 hyperactivity in DS rats is due to a deficient NOS, via the interactions cyclic GMP (cGMP)/cyclic AMP (cAMP) at the level of the thick ascending Henle's loop (TAL). DS rats DS (males, 250-300 g) and their normotensive controls DR ("salt-resistant") are sacrificed, the kidneys removed and NKCC2 activity is measured in medullary TAL (mTAL) as previously described. Medullary contents of NO are measured with a NitroFlux analyser by heat-reduction of nitrates and nitrites to NO. AMPc levels in mTAL are measured by an EIA immunotest. Neither L-NAME (3 mM), nor L-arginine were able to modify NKCC2 activity in mTAL from DS (pre-hypertensive) or DR rats. Levels of NO in the medullary interstitium and AMPc in mTAL were not significantly different between DS and DR rats. Conversely, in DS rats charged with 2% salt (in the food) during 7 weeks, L-arginine significantly inhibited NKCC2 in DS (35.6 +/- 6.8 vs 25.3 +/- 4.9 nmoles/mg protein/min; p<0.05 non-paired Student's t-test), but not in DR rats. In conclusion, NKCC2 in our mTAL preparation of prehypertensive DS and DR rats is insensitive to L-NAME and L-arginine. This suggests the absence of a functional NOS. NKCC2 hyperactivity of prehypertensive DS is therefore not due to a deficient NOS. This was confirmed by the normal levels of interstitial NO and mTAL cAMP in prehypertensive DS rats. Finally, a salt-load seems to induce NOS expression in mTAL of DS rats. This last observation deserves further investigation.
Alvarez-Guerra
M
M
INSERM U400, Faculté de médecine, Créteil.
Lou
M
M
Garay
R P
RP
D000818:Animals; D004195:Disease Models, Animal; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D009569:Nitric Oxide / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000494:pharmacology*; D051381:Rats; D020303:Rats, Inbred Dahl; D012965:Sodium Chloride / Q000378:metabolism* / Q000493:pharmacokinetics*; D028021:Sodium-Potassium-Chloride Symporters / Q000235:genetics* / Q000494:pharmacology*; D064466:Solute Carrier Family 12, Member 1
C578716:Slc12a1 protein, rat; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D009569:Nitric Oxide; D012965:Sodium Chloride; D019001:Nitric Oxide Synthase