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Our aim was to investigate whether blockade of calcium channels (CCs) or angiotensin II type 1 receptors (AT1R) modulates renal responses to nitric oxide synthesis inhibition (NOSI) in humans. Fourteen sodium-replete, healthy volunteers underwent 90-min infusions of 3.0 μg·kg−1·min−1 NG-nitro-l-arginine methyl ester (l-NAME) on 3 occasions, preceded by 3 days of either placebo (PL), 10 mg of manidipine (MANI), or 50 mg of losartan (LOS). At each phase, mean arterial pressure (MAP), glomerular filtration rate (GFR; inulin), renal blood flow (RBF; p-aminohippurate), urinary sodium (UNaV), and 8-isoprostane (U8-iso-PGF2αV; an oxidative stress marker) were measured. With PL + l -NAME, the following changes were observed: +6% MAP (P < 0.005 vs. baseline), −10% GFR, −20% RBF, −49% UNaV (P < 0.001), and +120% U8-iso-PGF2αV (P < 0.01). In contrast, MAP did not increase during LOS + l-NAME or MANI + l-NAME (P > 0.05 vs. baseline), whereas renal changes were the same during LOS + l-NAME vs. PL + l-NAME (ANOVA, P > 0.05). However, during MANI + l-NAME, changes vs. baseline in GFR (−6%), RBF (−12%), and UNaV (−34%) were blunted vs. PL + l-NAME and LOS + l-NAME (P < 0.005), and the rise in U8-iso-PGF2αV was almost abolished (+37%, P > 0.05 vs. baseline; P < 0.01 vs. PL + l-NAME or LOS + l-NAME). We conclude that, since MANI blunted l-NAME-induced renal hemodynamic changes, CCs participate in the renal responses to NOSI in healthy, sodium-replete humans independent of changes in MAP and without the apparent contribution of the AT1R. Because the rise in U8-iso-PGF2αV was essentially prevented during MANI + l-NAME, CC blockade may oppose the renal effects of NOSI in part by counteracting oxidative stress responses to acutely impaired renal NO bioavailability. [ABSTRACT FROM AUTHOR]

The objective is to elucidate the effect of nitric oxide (NO)-renin-angiotensin system (RAS) interactions on renal hemodynamic function in uncomplicated, type 1 diabetes mellitus (DM). In 14 salt-replete, male healthy volunteers (C) and 9 male DM patients on euglycemia, glomerular filtration rate (GFR), renal blood flow (RBF), filtration fraction (FF), and sodium excretion (UNaV) were measured at base-line and during a 90-min infusion of 3.0 μ.g-kg-1·min-1 NG-nitro-L-arginine-methyl-ester (L-NAME) after 3 days of pretreatment with either placebo (PL) or 50 mg losartan (LOS). Baseline GFR, RBF, and FF were higher in DM (P < 0.005). In the C group, PL + L-NAME caused declines in GFR (101 ± 3 to 90 ± 3 ml·min-1·1.73 m-2), RBF (931 ± 22 to 754 ± 31 ml·min-1·1.73 m-2), and UNaV (158 ± 12 to 82 ± 18 μmol/min) and an increase in FF (0.19 ± 0.02 to 0.21 ± 02; P < 0.001), which were not influenced by LOS pretreatment (P > 0.05 for LOS + L-NAME-C vs. PL + L-NAME-C). In DM, PL + L-NAME resulted in exaggerated renal effects, with changes in GFR (128 ± 3 to 104 ± 3 ml·min-1·1.73 m-2), RBF (1,019 ± 27 to 699 ± 34 ml·min-1·1.73 m-2), UNaV (150 ± 13 to 39 ± 14 μmol/min), and FF (0.22 ± 0.03 to 0.26 ± 0.02) that were significantly greater vs. PL + L-NAME-C (P < 0.005). LOS pretreatment blunted GFR, RBF, FF, and UNaV responses to L-NAME in DM (P < 0.005 vs. PL + L-NAME-DM), resulting in a response profile that was similar to PL + L-NAME and LOS + L-NAME in C (P > 0.05). Renal responses to L-NAME in uncomplicated, type 1 DM are exaggerated vs. C, consistent with an upregulation of NO bioactivity. LOS, without effects in C, prevents the accentuated actions of L-NAME in DM, thus indicating an augmented role for NO-RAS interactions in renal hemodynamic function in DM. [ABSTRACT FROM AUTHOR]

According to the "tubulocentric" hypothesis of the glomerular hyperfiltration of diabetes mellitus (DM), tubuloglomerular feedback (TGF) is the critical determinant of the related renal hemodynamic dysfunction. To examine the role of TGF in human type 1 DM, 12 salt-replete healthy (C) and 11 uncomplicated DM individuals underwent measurements of glomerular filtration rate (GFR), renal blood flow (RBF), and lithium-derived absolute "distal" sodium delivery (DDNa). Measurements were made during two 3-h infusions of 0.012 mmol·kg-1·min-1 L-arginine (ARG) buffered with either equimolar HCl (ARG.HCl) or citric acid (ARG.CITR). Our hypothesis was that changes in TGF signaling would be directionally opposite ARG.HCl vs. ARG.CITR according to the effects of the ARG-buffering anion on DDNa. Similar changes in C and DM followed ARG.CITR, with declines in DDNa (-0.26 ± 0.07 mmol/min C vs. -0.31 ± 0.07 mmol/min DM) and increases in RBF (+299 ± 25 vs. +319 ± 29 ml·min-1·1.73 m-2) and GFR (+6.6 ± 0.8 vs. +11.6 ± 1.2 ml·min-1.1.73 m-2). In contrast, with ARG.HCl, DDNa rose in both groups (P = 0.001), but the response was 73% greater in DM (+1.50 ± 0.15 mmol/min C vs. +2.59 ± 0.22 mmol/min DM, P = 0.001). RBF also increased (P = 0.001, +219 ± 20 ml·min-1·1.73 m-2 C, +105 ± 14 DM), but ΔRBF after ARG.HCl was lower vs. ARG.CITR in both groups (P = 0.001). After ARG.HCl, ΔRBF also was 50% lower in DM vs. C (P = 0.001) and GFR, unchanged in C, declined in DM (-7.4 ± 0.9 ml·min-1·1.73 m-2, P = 0.02 vs. C). After ARG.HCl, unlike ARG.CITR, DDNa increased in C and DM, associated with less ΔRBF and ΔGFR vs. ARG.CITR. This suggests that the renal hemodynamic response to ARG is influenced substantially by the opposite actions of HCl vs. CITR on DDNa and TGF. In DM, the association of ARG.HCl-induced exaggerated ΔDDNa, blunted ΔRBF, and the decline in GFR vs. C shows an enhanced TGF dependence of renal vasodilatation to ARG, in agreement with a critical role of TGF in DM-related renal hemodynamic dysfunction. [ABSTRACT FROM AUTHOR]