Increased nitric oxide synthase-3 expression in kidneys of deoxycorticosterone acetate-salt hypertensive rats

In addition to its hemodynamic effects, nitric oxide (NO) may play a role i n the renal tubular handling of sodium. Experiments were conducted to deter mine possible changes in renal nitric oxide synthase-3 (NOS3) expression in rats treated with deoxycorticosterone acetate (DOCA) and high salt. All ra ts were uninephrectomized, and either a placebo or DOCA pellet was implante d subcutaneously. Placebo-treated rats were then given tap water to drink a d libitum, and DOCA-treated rats received a 0.9% NaCl solution to drink. On ce a week, rats were placed in metabolic cages so that a 24-h urine sample could be collected. After 3 wk, the animals were sacrificed and the kidneys removed and prepared for subsequent immunohistochemical or Western blot an alysis. Urinary excretion of nitrate and nitrite (NOx) was measured to prov ide an indication of the intrarenal production of NO. DOCA-salt hypertensiv e rats exhibited increased urinary NOx excretion (2.43 +/- 0.48 mu mol NOx/ mg creatinine) compared with the placebo control animals (1.17 +/- 0.06 mu mol NOx/mg creatinine). Western blot analysis revealed that NOS3 protein le vels in both the cortex and medulla were greater in DOCA-salt rats compared with placebo-treated animals. Immunohistochemical analysis of kidneys reve aled that NOS3 expression in placebo rats was localized in vascular endothe lial cells with slight, but detectable, immunoreactivity in medullary colle cting ducts. In DOCA-salt rats, a very large increase in the intensity of i mmunostaining was detected in tubular epithelia of the proximal tubule, thi ck ascending limb of Henle's loop, and cortical and medullary collecting du ct; immunoreactivity in endothelial cells appeared unchanged. These data su ggest that increased tubular expression of NOS3 is responsible, at least in part, for the increased renal production of NO in DOCA-salt hypertension, and are consistent with a role for NO in the renal tubular response to salt loading.