Reduced endothelin-1– and nitric oxide–mediated arteriolar tone in hypertensive renal transplant recipients

Reduced endothelin-1– and nitric oxide–mediated arteriolar tone in hypertensive renal transplant recipients.BackgroundThe prevalence of hypertension is high in renal transplant recipients. It has been suggested that calcineurin inhibitors (CI) contribute to the development of post-transplant hypertension by stimulating endothelin (ET-1)-mediated and/or reducing nitric oxide (NO)-mediated vascular tone.MethodsWe tested this hypothesis using 2 groups of renal transplant recipients [normotensive patients without a need for antihypertensive medication (Normo-Tx), and hypertensive patients requiring antihypertensives (Hyper-Tx)] in the presence of CI-based immunosuppression. In addition, we studied matched control subjects (C). BQ 123 (ET-A receptor antagonist), BQ123 + BQ788 (ET-A/B-receptor antagonist), ET-1, L-NMMA (NO-synthase inhibitor), acetylcholine (ACH; endothelium-dependent vasodilator), glyceroltrinitrate (GTN, NO donor), and norepinephrine (NE, endothelium-independent vasoconstrictor) were infused into the brachial artery. Forearm blood flow (FBF) was measured by venous occlusion plethysmography.ResultsEndothelium-independent vasomotion in response to GTN and NE was similar in all groups. Vascular responses to selective and combined blockade of ET receptors in both Normo-Tx and Hyper-Tx did not exceed those of C. In fact, we observed a significantly lower increase in FBF after BQ 123 (P = 0.03), as well as after BQ 123/788 (P = 0.03) in Hyper-Tx compared with Normo-Tx. This was associated with an increased vascular sensitivity to exogenous ET-1 in Hyper-Tx compared with Normo-Tx (P = 0.04). Vasoconstriction after L-NMMA was reduced in Hyper-Tx compared with Normo-Tx (P = 0.015), while the response to ACH was reduced in both groups of Tx patients to a similar degree (P = 0.005 vs. C).ConclusionOur results do not support a major role for the vascular endothelin system in the hypertension of renal transplant recipients, whereas deficient baseline NO production may be a contributing factor

Hydroxyfasudil-Mediated Inhibition of ROCK1 and ROCK2 Improves Kidney Function in Rat Renal Acute Ischemia-Reperfusion Injury

Renal ischemia-reperfusion (IR) injury (IRI) is a common and important trigger of acute renal injury (AKI). It is inevitably linked to transplantation. Involving both, the innate and the adaptive immune response, IRI causes subsequent sterile inflammation. Attraction to and transmigration of immune cells into the interstitium is associated with increased vascular permeability and loss of endothelial and tubular epithelial cell integrity. Considering the important role of cytoskeletal reorganization, mainly regulated by RhoGTPases, in the development of IRI we hypothesized that a preventive, selective inhibition of the Rho effector Rho-associated coiled coil containing protein kinase (ROCK) by hydroxyfasudil may improve renal IRI outcome. Using an IRI-based animal model of AKI in male Sprague Dawley rats, animals treated with hydroxyfasudil showed reduced proteinuria and polyuria as well as increased urine osmolarity when compared with sham-treated animals. In addition, renal perfusion (as assessed by 18F-fluoride Positron Emission Tomography (PET)), creatinine- and urea-clearances improved significantly. Moreover, endothelial leakage and renal inflammation was significantly reduced as determined by histology, 18F-fluordesoxyglucose-microautoradiography, Evans Blue, and real-time PCR analysis. We conclude from our study that ROCK-inhibition by hydroxyfasudil significantly improves kidney function in a rat model of acute renal IRI and is therefore a potential new therapeutic option in humans

The Na-K-ATPase is a target for an EDHF displaying characteristics similar to potassium ions in the porcine renal interlobar artery

1. The present study was performed to determine the characteristics of the endothelium-derived hyperpolarizing factor (EDHF) that mediates the nitric oxide (NO)- and prostacyclin (PGI(2))-independent hyperpolarization and relaxation of porcine renal interlobar arteries. 2. Bradykinin-induced changes in isometric force or smooth muscle membrane potential were assessed in rings of porcine renal interlobar artery preconstricted with the thromboxane analogue U46619 in the continuous presence of N(ω)-nitro-L-arginine and diclofenac to inhibit NO synthases and cyclo-oxygenases. 3. Inhibition of NO- and PGI(2)-production induced a rightward shift in the concentration-relaxation curve to bradykinin without affecting maximal relaxation. EDHF-mediated relaxation was abolished by a depolarizing concentration of KCl (40 mM) as well as by a combination of charybdotoxin and apamin (each 100 nM), two inhibitors of calcium-dependent K(+) (K(+)(Ca)) channels. Charybdotoxin and apamin also reduced the bradykinin-induced, EDHF-mediated hyperpolarization of smooth muscle cells from 13.7±1.3 mV to 5.7±1.2 mV. 4. In addition to the ubiquitous α1 subunit of the Na-K-ATPase, the interlobar artery expressed the γ subunit as well as the ouabain-sensitive α2, α3 subunits. A low concentration of ouabain (100 nM) abolished the EDHF-mediated relaxation and reduced the bradykinin-induced hyperpolarization of smooth muscle cells (13.6±2.8 mV versus 5.20±1.39 mV in the absence and presence of ouabain). 5. Chelation of K(+), using cryptate 2.2.2., inhibited EDHF-mediated relaxation, without affecting NO-mediated responses. Elevating extracellular KCl (from 4 to 14 mM) elicited a transient, ouabain-sensitive hyperpolarization and relaxation that was endothelium-independent and insensitive to charybdotoxin and apamin. 6. These results indicate that in the renal interlobar artery, EDHF-mediated responses display the pharmacological characteristics of K(+) ions released from endothelial K(+)(Ca) channels. Smooth muscle cell hyperpolarization and relaxation appear to be dependent on the activation of highly ouabain-sensitive subunits of the Na-K-ATPase