Feasibility of Percutaneous Ultrasound Guided Intervention with Direct Access in Failing Infrainguinal Vein Bypass Grafts.

BACKGROUND: Patients with infrainguinal venous bypass grafts are at risk of graft stenosis leading to thrombosis and failure of the graft conduit. When primary assisted reintervention is needed, a common first choice of treatment is percutaneous angioplasty using fluoroscopy and digital subtraction angiography (DSA). We investigated whether percutaneous ultrasound-guided intervention (PUSGI) is feasible for such endovascular reinterventions. METHODS: In this retrospective observational study (feasibility study), we included patients with ultrasound evidence of significant stenosis in below-the-knee vein grafts in the lower extremities. Inclusion period was 18 months. Reinterventions were disrupted by performing PUSGI in between traditional DSA. Perioperative success was defined as no sign of residual stenosis, stenosis at the access point in the vein, or need for further fluoroscopy guided intervention. Patient follow-up was conducted 6 weeks after the intervention. Patency of the procedure was defined as no disease recurrence or signs of ultrasonographic restenosis at follow-up. RESULTS: PUSGI was performed in 17 patients referred for reintervention with imminent failing grafts (12 men, 5 women, age range 52-82 years). PUSGI alone was performed successfully in 10 out of 17 patients (59%). The remaining 7 patients underwent successful revascularization with PUSGI in combination with DSA-guided angioplasty. Periprocedural complications occurred in 4 patients. Two of 17 patients had occluded grafts at 6 weeks of follow-up. No PUSGI access site stenoses in grafts were observed. CONCLUSIONS: Percutaneous ultrasound-guided reintervention in peripheral vein bypass disease is feasible for selected patients. The study provides insight to qualitative criteria of eligibility for PUSGI in such reinterventions with direct conduit access.

Echolucent Carotid Plaques Becomes More Echogenic over Time - A 3D Ultrasound Study.

BACKGROUND: Despite the presence of only a few established risk factors, some patients will experience atherosclerotic events. Therefore, methods for improved risk stratification for atherosclerotic events are wanted. We aimed to detect changes in carotid artery atherosclerotic plaque volume and echogenicity over time in patients with an acute thromboembolic event and in patients with chronic atherosclerotic disease, both treated with statin, using a novel 3D ultrasound system. METHODS: We included two cohorts of patients; 70 patients, naïve to statin treatment, admitted with acute, first-time myocardial infarction (aMI), and 69 patients who had been on statin treatment for a minimum of 6 months with chronic peripheral arterial disease (cPAD). 3D ultrasound examination was performed at baseline and after 3 and 12 months. Plaque volume was quantified in 3D ultrasound plaque acquisitions, and echogenicity was assessed using grayscale median (GSM) and normalized with adventitia as reference. RESULTS: The aMI group had darker plaques than the cPAD group at baseline (mean GSM: 60.98, standard deviation (SD): 24.09 vs. 71.75, SD: 21.55; P = 0.006), 3 months (63.64, SD: 20.47 vs. 73.44, SD: 20.46; P = 0.006) and at 12 months follow-up (59.25, SD: 18.07 vs. 71.02, SD: 22.31; P = 0.004). The differences were not significant after adjusting for traditional risk factors. Dividing both groups by the median GSM, the darkest half of the aMI group's had an increase in GSM mainly within the first 3 months (10.49, CI 95%: 2.45 to 18.53; P = 0.012) and hereafter remained unchanged at 12 months follow-up (-0.53, CI 95%: -7.28 to 6.22, P = 0.875). In the darkest cPAD group GSM also increased within 3 months (8.14, CI 95%: 1.85-14.32, P = 0.012) and hereafter stabilized till 12 months (-2.54, CI 95%: -9.62 to 4.53, P = 0.475). Plaque volume did not change in the aMI group from baseline (median: 55.41 mm3, interquartile range (IQR): 24.24-84.31) to 12 months (58.67 mm3, IQR: 31.81-93.51) (P = 0.220) whereas there was a small decrease in the cPAD group from baseline (71.63 mm3, IQR: 40.12-135.61) to 12 months (67.73 mm3, IQR: 31.00-122.38) (P = 0.026). CONCLUSIONS: Echolucent carotid plaque, assessed with the novel 3D matrix ultrasound system, had increasing GSM within 3 months period, indicating stabilization of the more vulnerable plaques in aMI and cPAD patients. Plaque volume decreased over 12 months follow-up in a long-term statin-treated patient with cPAD, but not during the first 12 months statin therapy in patients with aMI.

Ensuring Competency in Open Aortic Aneurysm Repair - Development and Validation of a New Assessment Tool.

OBJECTIVE: The aims of this study were to develop a procedure specific assessment tool for open abdominal aortic aneurysm (AAA) repair, gather validity evidence for the tool and establish a pass/fail standard. METHODS: Validity was studied based on the contemporary framework by Messick. Three vascular surgeons experienced in open AAA repair and an expert in assessment and validation within medical education developed the OPEn aortic aneurysm Repair Assessment of Technical Expertise (OPERATE) tool. Vascular surgeons with varying experiences performed open AAA repair in a standardised simulation based setting. All procedures were video recorded with the faces anonymised and scored independently by three experts in a mutual blinded setup. The Angoff standard setting method was used to establish a credible pass/fail score. RESULTS: Sixteen novices and nine experienced open vascular surgeons were enrolled. The OPERATE tool achieved high internal consistency (Cronbach's alpha .92) and inter-rater reliability (Cronbach's alpha .95) and was able to differentiate novices and experienced surgeons with mean scores (higher score is better) of 13.4 ± 12 and 25.6 ± 6, respectively (p = .01). The pass/fail score was set high (27.7). One novice passed the test while six experienced surgeons failed. CONCLUSION: Validity evidence was established for the newly developed OPERATE tool and was able to differentiate between novices and experienced surgeons providing a good argument that this tool can be used for both formative and summative assessment in a simulation based environment. The high pass/fail score emphasises the need for novices to train in a simulation based environment up to a certain level of competency before apprenticeship training in the clinical environment under the tutelage of a supervisor. Familiarisation with the simulation equipment must be ensured before performance is assessed as reflected by the low scores in the experienced group's first attempt.

Congestive heart failure in rats is associated with increased collecting duct vasopressin sensitivity and vasopressin type 2 receptor reexternalization.

A number of studies have shown that rats with congestive heart failure (CHF) have increased protein levels of the vasopressin (AVP)-regulated water channel aquaporin-2 (AQP2) even during conditions with unchanged circulating levels of AVP, suggesting an increase in the sensitivity of the AVP type 2 (V2) receptor in experimental CHF. The present study was aimed at investigating AVP signaling in rats with moderate CHF (left ventricular end diastolic pressure >10 mmHg; normal plasma AVP levels) induced by ligation of the left anterior descending coronary artery. Sham-operated rats were used as controls. Western blotting analyses revealed an increased abundance of AQP2 in renal cortex (+33 ± 9% of sham; P < 0.05) and in inner medulla (IM) (+54 ± 15% of sham; P < 0.05) in CHF rats compared with sham-operated controls. Dose-response studies on isolated collecting ducts (CDs) showed an increased accumulation of cAMP in response to AVP in CHF rats compared with controls. V2 receptor surface-binding studies in isolated IMCDs showed a marked and comparable AVP-induced V2 receptor internalization in response to AVP in both CHF and control rats. As expected V2 receptor surface binding remained low after AVP challenge in control rats. In contrast to this, V2 receptor surface binding returned to pre-AVP levels within 30 min in the CHF rats, indicating an obtained recycling ability of the V2 receptor in CHF. Together the results indicate the presence of an increased AVP sensitivity in the CDs from CHF rats, associated with an acquired recycling ability of the V2 receptor.

Carotid plaque inflammatory activity assessed by 2-[18F]FDG-PET imaging decrease after a neurological thromboembolic event.

BACKGROUND: Atherosclerotic plaque vulnerability is comprised by plaque composition driven by inflammatory activity and these features can be depicted with 3D ultrasound and 2-[18F]FDG-PET, respectively. The study investigated timely changes in carotid artery plaque inflammation and morphology after a thromboembolic event with PET/CT and novel ultrasound volumetric grayscale median (GSM) readings. Patients with a single hemisphere-specific neurological symptom and the presence of an ipsilateral carotid artery atherosclerotic plaque were prospectively included to both 2-[18F]FDG PET/CT and 3D ultrasound scans of the plaque immediately after their event and again three months later. On PET/CT images the maximum standardized uptake value (SUVmax) was measured and the volumetric ultrasound acquisitions were analyzed using a semiautomated software measuring GSM values. RESULTS: Baseline scans were performed by a mean of 7 days (range 2-14) after the symptom and again after 98 days (range 91-176). For the entire group (n = 14), we found a decrease in average SUVmax from baseline to follow-up of - 0.18 (95% confidence interval: - 0.34 to - 0.02, P = 0.034). GSM did not increase significantly over time (mean change: + 2.21, 95% confidence interval: - 17.02 to 21.44, P = 0.808). CONCLUSION: A decrease in culprit lesion 2-[18F]FDG-uptake 3 months after an event indicates a decrease in inflammatory activity, suggesting that carotid plaque stabilization over time. 3D ultrasound morphological quantitative differences in GSM were not detectable after 3 months.

Patients with Unstable Atherosclerosis Have More Echolucent Carotid Plaques Compared with Stable Atherosclerotic Patients: A 3-D Ultrasound Study.

Using a novel 3-D ultrasound system, we aimed to determine differences in carotid plaque size and echogenicity in two atherosclerotic groups. Seventy patients admitted with acute myocardial infarction (aMI) and 69 patients known with chronic peripheral arterial disease (cPAD) were included. The cPAD group had larger plaque volumes (median: 70.24 mm3, interquartile range [40.12-135.61] vs. 55.41 mm3 [4.24-84.31], p = 0.004), thicker plaques (2.45 mm [1.85-3.25] vs. 1.99 mm [1.55 - 2.64], p = 0.005) and higher gray-scale medians (GSMs) (mean: 71.75, standard deviation: 21.55 vs. 60.99 [24.09], p = 0.006) than the aMI group. After adjustment for traditional risk factors, the difference persisted for thickness and volume. The difference in GSM persisted after adjustment for volume only. Patients with stable atherosclerotic disease had larger and brighter carotid plaques compared with unstable atherosclerotic patients. 3-D ultrasound may prove useful in identifying thromboembolic risk.

Reproducibility of two 3-D ultrasound carotid plaque quantification methods.

Compared with single 2-D images, emerging 3-D ultrasound technologies hold the promise of reducing variability and increasing sensitivity in the quantification of carotid plaques for individual cardiovascular risk stratification. Inter- and intra-observer agreement between a manual, cross-sectional, 2-D freehand sweep and a mechanical 3-D ultrasound investigation of 62 carotid artery plaques is reported with intra-class correlation coefficients (with 95% confidence intervals). Inter-observer agreement was 0.60 (0.29-0.77) for the freehand method and 0.89 (0.83-0.93) for the mechanical 3-D acquisition. The use of semi-automated computerized planimetric measurements of plaque burden has high intra-observer repeatability, but is vulnerable to systematic inter-observer differences. For the 2-D freehand sweep, a considerable contribution to variation is introduced by the scanning procedure itself, that is, the lack of controlled motion along the third dimension. Future implementation of 3-D ultrasound quantification in large-scale studies of inter-individual cardiovascular risk assessment seems justified using the methods described.

(18)F-FDG imaging of human atherosclerotic carotid plaques reflects gene expression of the key hypoxia marker HIF-1α.

To investigate the association between gene expression of key molecular markers of hypoxia and inflammation in atherosclerotic carotid lesions with 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG) uptake as determined clinically by positron emission tomography (PET). Studies using PET have demonstrated (18)F-FDG-uptake in patients with confirmed plaques of the carotid artery. Inflammatory active or "vulnerable" plaques progressively increase in bulk, develop necrotic cores, poor vessel-wall vascularization and become prone to hypoxia. We used quantitative polymerase-chain reaction (qPCR) to determine gene expression of hypoxia-inducible factor 1α (HIF-1α) and cluster of differentiation 68 (CD68) on plaques recovered by carotid endarterectomy (CEA) in 18 patients. Gene expression was compared with (18)F-FDG-uptake quantified as the maximum standardized uptake value (SUVmax) on co-registered PET/computed tomography (CT) scans performed the day before CEA. Immunohistochemistry was used to validate target-gene protein expression. In univariate linear regression analysis HIF-1α was significantly correlated with (18)F-FDG-uptake (SUVmax) as was CD68. A two-tailed Pearson regression model demonstrated that HIF-1α and CD68 gene expression co-variated and accordingly when entering the variables into multivariate linear regression models with SUV-values as dependent variables, HIF-1α was eliminated in the final models. (18)F-FDG-uptake (SUVmax) is correlated with HIF-1α gene expression indicating an association between hypoxia and glucose metabolism in vivo. The marker of inflammation CD68 is also associated with (18)F-FDG-uptake (SUVmax). As CD68 and HIF-1α gene expression co-variate their information is overlapping.

Microvessel density but not neoangiogenesis is associated with 18F-FDG uptake in human atherosclerotic carotid plaques.

INTRODUCTION: The vulnerable atherosclerotic lesion exhibits the proliferation of neovessels and inflammation. The imaging modality 2-deoxy-2-[(18)F]fluoro-D: -glucose positron emission tomography ((18)FDG-PET) is considered for the identification of vulnerable plaques. PURPOSE: The purpose of this study was to compare the gene expression of neoangiogenesis and vulnerability-associated genes with (18)FDG uptake in patients undergoing carotid endarterectomy. PROCEDURES: Human atherosclerotic carotid artery plaques from symptomatic patients were used for gene expression analysis by quantitative PCR of vascular endothelial growth factor (VEGF) and integrin α(V) and integrin ß(3) subunits, genes essential during neoangiogenesis. We also evaluated the gene expression of CD34, a measure of microvessel density (MVD), as well as CD68, MMP-9, and cathepsin K, genes of major importance in plaque vulnerability. Gene expression analysis was compared with (18)FDG-PET. RESULTS: VEGF and integrin α(V)ß(3) gene expression did not correlate with (18)FDG uptake, whereas CD34 gene expression exhibited an inverse correlation with (18)FDG uptake. Additionally, we established that markers of vulnerability were correlated with (18)FDG uptake. CONCLUSIONS: Neoangiogenesis is not associated with (18)FDG uptake, whereas MVD and markers of vulnerability correlate with (18)FDG uptake. The absence of correlation between markers of neoangiogenesis and (18)FDG uptake suggests a temporal separation between the process of neoangiogenesis and inflammatory activity.

When to image carotid plaque inflammation with FDG PET/CT.

OBJECTIVE: Quantification of 18-fluorodeoxyglucose (FDG) uptake in inflamed high-risk carotid atherosclerotic plaques is challenged by the spatial resolution of positron emission tomography (PET) and luminal blood activity. Late acquisition protocols have been used to overcome these challenges to enhance the contrast between the plaque and blood-pool FDG activity. However, for prospective studies the late acquisition is inconvenient for the patient and staff, and most retrospective studies of plaque uptake use data from early acquisition protocols. The objective was to evaluate changes in the quantification methods of FDG uptake in carotid artery plaques between early and late PET scans. METHODS: FDG uptake 1 and 3 h after tracer injection was compared in 19 carotid artery plaques. The average plaque maximum standardized uptake value (SUVmax) and a target to background ratio (TBR), using venous blood-pool activity as background, were evaluated at the two time points. These methods have been shown earlier to quantitate the degree of inflammation in late hour scans. RESULTS: A good individual plaque FDG uptake consistency was found between the two time points for SUVmax, r²=0.86. In contrast, the ratio method did not conserve the results between the two time points: TBR r²=0.34. For both methods, absolute values changed over time. TBR values generally increased as blood pool activity decreased, whereas the individual plaque SUVmax values showed both increases and decreases over time. CONCLUSION: Identification of carotid plaque inflammation with PET can be performed 1 h after FDG injection using SUVmax for plaque FDG uptake quantification.

18FDG PET and ultrasound echolucency in carotid artery plaques.

OBJECTIVES: The objective was to evaluate inflammation in echolucent carotid artery plaques. BACKGROUND: Ultrasound echolucency of carotid artery plaques has been proven to differentiate patients at high risk of stroke. On the other hand, positron emission tomography (PET) of plaques with the use of [(18)F]-fluorodeoxyglucose (FDG) identifies highly inflamed plaques, and the combination of molecular imaging and morphology could improve identification of vulnerable plaques. METHODS: A total of 33 patients with cerebrovascular symptoms and carotid artery plaques were included prospectively for ultrasound and PET imaging. Plaque standardized gray scale medians (GSM) were measured in longitudinal ultrasound images to quantitate echolucency, and GSM values were compared with FDG PET uptake quantified by maximum standardized uptake values (SUV). Symptomatic plaques were compared with contralateral carotid artery plaques considered asymptomatic, and in 17 symptomatic patients, endarterectomized plaque specimens were analyzed for CD68 expression. RESULTS: There was a negative correlation between GSM and FDG SUV (r = -0.56, p < 0.01). Whereas echo-rich plaques tended to show low FDG uptake, echolucent plaques ranged from high to low inflammatory activity, as depicted with PET. Quantitative FDG SUV differentiated asymptomatic from symptomatic plaques, whereas GSM values did not. There was a positive correlation between CD68 expression and FDG uptake (r = 0.50, p = 0.04). CONCLUSIONS: Our results substantiate previous findings of an association between plaque FDG uptake and inflammation. Echolucent plaques exhibit a wide range of inflammatory activity, whereas echorich plaques show little inflammation. FDG PET may be useful for further stratification of echolucent plaques being either active (vulnerable) or inactive.

Gene expression and 18FDG uptake in atherosclerotic carotid plaques.

PURPOSE: Metabolic assessment of vascular inflammation by 2-[F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG)-PET is a promising new approach for the evaluation of the vulnerability of atherosclerotic plaques. Quantitative real-time PCR allows measurement of gene expression of markers of atherosclerotic plaque vulnerability. These techniques were applied in advanced atherosclerotic disease to relate metabolism and inflammatory activity to the gene expression profile of the vulnerable atherosclerotic plaque. METHODS: Seventeen patients with clinical symptoms of cerebral vascular events (<3 months) and an additional ipsilateral internal carotid artery stenosis of greater than 60% were recruited. FDG uptake in the carotids was determined by PET/computed tomography and expressed as mean and maximal standardized uptake values (SUVmean and SUVmax). The atherosclerotic plaques were subsequently recovered by carotid endarterectomy. The gene expression of markers of vulnerability - CD68, IL-18, matrix metalloproteinase 9, cathepsin K, GLUT-1, and hexokinase type II (HK2) - were measured in plaques by quantitative PCR. RESULTS: In a multivariate linear regression model, GLUT-1, CD68, cathepsin K, and HK2 gene expression remained in the final model as predictive variables of FDG accumulation calculated as SUVmean (R=0.26, P<0.0001). In addition, a multivariate linear regression model found GLUT-1, CD68, cathepsin K, and HK2 gene expression as independent predictive variables of FDG accumulation calculated as SUVmax (R=0.30, P<0.0001). CONCLUSION: GLUT-1, HK2, CD68, and cathepsin K remained in both multivariate models and thus provided independent information regarding FDG uptake. We suggest that FDG uptake is a composite indicator of macrophage load, overall inflammatory activity and collagenolytic plaque destabilization. Accordingly, FDG-PET could prove to be an important predictor of cerebrovascular events in patients with carotid plaques.

Effects of renal denervation on tubular sodium handling in rats with CBL-induced liver cirrhosis.

This study was designed to examine the effect of bilateral renal denervation (DNX) on thick ascending limb of Henle's loop (TAL) function in rats with liver cirrhosis induced by common bile duct ligation (CBL). The CBL rats had, as previously shown, sodium retention associated with hypertrophy of the inner stripe of the outer medulla (ISOM) and increased natriuretic effect of furosemide in vivo, and semiquantitative immunoblotting showed increased expression of the furosemide-sensitive Na-K-2Cl cotransporter type 2 (NKCC2) in ISOM from CBL rats. DNX significantly attenuated the sodium retention in the CBL rats, which was associated with normalization of the natriuretic effect of furosemide, as well as a significant reduction in the expression of NKCC2 in the ISOM. However, the marked hypertrophy of the ISOM found in CBL rats was not reversed by DNX. Together, these data indicate that increased renal sympathetic nerve activity known to be present in CBL rats plays a significant role in the formation of sodium retention by stimulating sodium reabsorption in the TAL via increased renal abundance of NKCC2.

Uncoupling of vasopressin signaling in collecting ducts from rats with CBL-induced liver cirrhosis.

Vasopressin (AVP) stimulates collecting duct water reabsorption through cAMP-mediated membrane targeting and increased expression of the aquaporin-2 (AQP2) water channel. Rats with liver cirrhosis induced by common bile duct ligation (CBL) show decreased protein expression of AQP2 despite increased plasma concentrations of AVP. The present study was conducted to investigate possible mechanisms behind this uncoupling of AVP signaling. The rats were examined 4 wk after CBL or sham operation. The CBL rats had increased plasma AVP concentrations (CBL: 3.2 +/- 0.2 vs. sham: 1.4 +/- 0.4 pg/ml, P < 0.05) and reduced AQP2 (0.62 +/- 0.11) and phosphorylated AQP2 (0.50 +/- 0.06) protein expression compared with sham-operated rats. However, examination of subcellular AQP2 localization by immunohistochemistry showed unchanged plasma membrane targeting in CBL rats, indicating a sustained ability of AQP2 short-term regulation. In a separate series of animals, thirsting was found to normalize AQP2 expression, indicating that AVP uncoupling in CBL rats is a physiological compensatory mechanism aimed at avoiding dilutional hyponatremia. Studies on microdissected collecting ducts from CBL rats showed decreased cAMP accumulation in response to AVP stimulation. The presence of the nonspecific phosphodiesterase inhibitor IBMX normalized the cAMP accumulation, indicating that cAMP-phosphodiesterase activity is increased in CBL rats. However, in contrast to this, Western blotting showed a decreased expression of several phosphodiesterase splice variants. We conclude that CBL rats develop an escape from AVP to prevent the formation of dilutional hyponatremia in response to increased plasma AVP concentrations. The mechanism behind AVP escape seems to involve decreased collecting duct sensitivity to AVP as a result of increased cAMP-phosphodiesterase activity.

Lipopolysaccharide-induced acute renal failure in conscious rats: effects of specific phosphodiesterase type 3 and 4 inhibition.

In conscious, chronically instrumented rats we examined 1) renal tubular functional changes involved in lipopolysaccharide (LPS)-induced acute renal failure; 2) the effects of LPS on the expression of selected renal tubular water and sodium transporters; and 3) effects of milrinone, a phosphodiesterase type 3 (PDE3) inhibitor, and Ro-20-1724, a PDE4 inhibitor, on LPS-induced changes in renal function. Intravenous infusion of LPS (4 mg/kg b.wt. over 1 h) caused an immediate decrease in glomerular filtration rate (GFR) and proximal tubular outflow without changes in mean arterial pressure (MAP). LPS-induced fall in GFR and proximal tubular outflow were sustained on day 2. Furthermore, LPS-treated rats showed a marked increase in fractional distal water excretion, despite significantly elevated levels of plasma vasopressin (AVP). Semiquantitative immunoblotting showed that LPS increased the expression of the Na(+),K(+),2Cl(-)-cotransporter (BSC1) in the thick ascending limb, whereas the expression of the AVP-regulated water channel aquaporin-2 in the collecting duct (CD) was unchanged. Pretreatment with milrinone or Ro-20-1724 enhanced LPS-induced increases in plasma tumor necrosis factor-alpha and lactate, inhibited the LPS-induced tachycardia, and exacerbated the acute LPS-induced fall in GFR. Furthermore, Ro-20-1724-treated rats were unable to maintain MAP. We conclude 1) PDE3 or PDE4 inhibition exacerbates LPS-induced renal failure in conscious rats; and 2) LPS treated rats develop an escape from AVP in the CDs, which could be aimed to protect against water intoxication in septic conditions associated with decreased GFR and high levels of AVP.

Chronic nitric oxide synthase inhibition exacerbates renal dysfunction in cirrhotic rats.

The present study investigated sodium balance and renal tubular function in cirrhotic rats with chronic blockade of the nitric oxide (NO) system. Rats were treated with the nonselective NO synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME) starting on the day of common bile duct ligation (CBL). Three weeks of daily sodium balance studies showed that CBL rats developed sodium retention compared with sham-operated rats and that l-NAME treatment dose dependently deteriorated cumulative sodium balance by reducing urinary sodium excretion. Five weeks after CBL, renal clearance studies were performed, followed by Western blotting of the electroneutral type 3 sodium/proton exchanger (NHE3) and the Na-K-ATPase present in proximal tubules. Untreated CBL rats showed a decreased proximal reabsorption with a concomitant reduction of NHE3 and Na-K-ATPase levels, indicating that tubular segments distal to the proximal tubules were responsible for the increased sodium reabsorption. l-NAME-treated CBL rats showed an increased proximal reabsorption measured by the lithium clearance method and showed a marked increase in NHE3 and Na-K-ATPase protein levels. Our results show that chronic l-NAME treatment exacerbates the sodium retention found in CBL rats by a significant increase in proximal tubular reabsorption.

Opioid receptor-like 1 stimulation in the collecting duct induces aquaresis through vasopressin-independent aquaporin-2 downregulation.

Nociceptin, the endogenous ligand of the inhibitory G protein-coupled opioid receptor-like 1 receptor, produces aquaresis (i.e., increases the excretion of solute-free urine) in rats. However, the mechanism underlying this effect has not yet been explained. Using immunohistochemistry, we found the opioid receptor-like 1 receptor in the rat kidney colocalized with the vasopressin-regulated water channel aquaporin-2 in inner medullary collecting ducts. We investigated the aquaretic effect of opioid receptor-like 1 receptor stimulation by infusing the selective nociceptin analog ZP120C; volume depletion was prevented by computer-driven, servo-controlled intravenous volume replacement with 50 mM glucose. ZP120C induced a marked and sustained aquaresis in normal and congestive heart failure rats in the absence of changes in vasopressin plasma concentrations. The ZP120C-induced aquaresis was associated with downregulation of the aquaporin-2 protein level in both rat groups, suggesting that opioid receptor-like 1 receptor stimulation produces aquaresis by inhibiting the vasopressin type-2 receptor-mediated stimulation on collecting duct water reabsorption. However, substantial amounts of PKA-mediated serine 256 phosphorylated aquaporin-2 were still present after 4 h of ZP120C treatment. Furthermore, neither preincubation with nociceptin nor ZP120C inhibited vasopressin-mediated cAMP accumulation in isolated collecting ducts. We conclude that renal opioid receptor-like 1 receptor stimulation in normal and congestive heart failure rats produces aquaresis by a direct renal effect, via aquaporin-2 downregulation, through a mechanism not involving inhibition of vasopressin type-2 receptor-mediated cAMP production.