Renal Oxygenation Changes During Water Loading as Evaluated by BOLD MRI: Effect of NOS Inhibition

Purpose: To demonstrate a possible role for endogenous release of nitric oxide in determining the response of water loading on intrarenal oxygenation as evaluated by blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI). Materials and Methods: Twelve Sprague Dawley rats (weight 344.9 +/- 40.6 g) were equally divided into two groups, A and B. Water loading was implemented by continuous infusion of hypotonic saline containing glucose (0.25% NaCl, 0.5% glucose). Rats in group A were subject to water loading alone, while group B rats were dosed with N-nitro-L-arginine methyl ester, (L-NAME) (10.0 mg/kg) prior to water loading. T-2*-weighted images of the kidneys were obtained on a Siemens 3T Verio MRI scanner using a multiple gradient recalled echo (mGRE) sequence. Results: Consistent with previous reports, group A exhibited a significant decrease in medullary R-2* during water loading (40.64 +/- 1.10 s(-1) to 34.68 +/- 1.49 s(-1), P < 0.05). On the other hand, in group B there was no decrease in R-2* during water loading (48.11 +/- 2.38 s(-1) to 51.06 +/- 2.18 s(-1)). The increased prewater loading R-2* is due to the pretreatment with L-NAME (40.82 +/- 3.23 s(-1) to 48.11 +/- 2.38 s(-1), P < 0.05). Conclusion: Our data suggest for the first time a role for endogenous nitric oxide in determining the response of renal medullary oxygenation to water loading.