Angiotensin II type 2 receptor-mediated inhibition of NaCl absorption is blunted in thick ascending limbs from Dahl salt-sensitive rats.
NO reduces NaCl absorption by thick ascending limbs (TALs) by inhibiting the Na/K/2Cl cotransporter (NKCC2). We have shown that NO-induced inhibition of Na transport is reduced in Dahl salt-sensitive rat (SS) TALs. Angiotensin II increases NO production in TALs via angiotensin II type 2 receptor (AT(2)R). It is unknown whether AT(2)Rs regulate TAL NaCl absorption and whether this effect is reduced in SS rats. We hypothesized that AT(2)R activation decreases TAL Na transport via NO, and this effect is blunted in SS rats. In the presence of angiotensin II type 1 receptor antagonist losartan, AT(2)R activation with angiotensin II inhibited NKCC2 activity by 32±7% (P<0.03). AT(2)R antagonist PD-123319 abolished the effect of angiotensin II. Activation with the AT(2)R-selective agonist CGP42112A (10 nmol/L) decreased NKCC2 activity by 29±6% (P<0.03). The effect of CGP42112A on NKCC2 activity was blocked by PD-123319 and by NO synthase inhibitor N(G)-nitro-l-arginine methyl ester. In Dahl salt-resistant rat TALs, 1 nmol/L of CGP42112A decreased NKCC2 activity by 23±4% (P<0.01). In SS TALs, it had no effect. TAL AT(2)R mRNA did not differ in SS versus salt-resistant rats. We conclude the following: (1) TAL AT(2)R activation decreases Na absorption; (2) this effect is mediated by AT(2)R-induced stimulation of NO; (3) AT(2)R-induced reduction of NKCC2 activity is blunted in SS rats; and (4) defects in AT(2)R/NO signaling rather than decreased AT(2)R expression likely account for the blunted effect in SS TALs. Impaired AT(2)R-mediated signaling in TALs could contribute to the Na retention associated with salt-sensitive hypertension.
Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, 2799 West Grand Blvd, Detroit, MI 48202, USA.
Nancy J
NJ
Hong
Jeffrey L
JL
Garvin
D000042:Absorption / Q000187:drug effects; D057912:Angiotensin II Type 2 Receptor Blockers / Q000494:pharmacology; D000818:Animals; D004195:Disease Models, Animal; D006973:Hypertension / Q000378:metabolism* / Q000503:physiopathology; D007093:Imidazoles / Q000494:pharmacology; D008138:Loop of Henle / Q000187:drug effects / Q000378:metabolism*; D019808:Losartan / Q000494:pharmacology; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D020303:Rats, Inbred Dahl / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D044139:Receptor, Angiotensin, Type 2 / Q000819:agonists / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D012965:Sodium Chloride / Q000378:metabolism*; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D064466:Solute Carrier Family 12, Member 1
D057912:Angiotensin II Type 2 Receptor Blockers; D007093:Imidazoles; D009842:Oligopeptides; D011725:Pyridines; D044139:Receptor, Angiotensin, Type 2; C578716:Slc12a1 protein, rat; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; C060894:CGP 42112A; C073402:PD 123319; D009569:Nitric Oxide; D012965:Sodium Chloride; D019808:Losartan