Angiotensin II and the Renal Hemodynamic Response to an Isolated Increased Renal Venous Pressure in Rats

Elevated central venous pressure increases renal venous pressure (RVP) which can affect kidney function. We previously demonstrated that increased RVP reduces renal blood flow (RBF), glomerular filtration rate (GFR), and renal vascular conductance (RVC). We now investigate whether the RAS and RBF autoregulation are involved in the renal hemodynamic response to increased RVP. Angiotensin II (ANG II) levels were clamped by infusion of ANG II after administration of an angiotensin-converting enzyme (ACE) inhibitor in male Lewis rats. This did not prevent the decrease in ipsilateral RBF (−1.9±0.4ml/min, p<0.05) and GFR (−0.77±0.18ml/min, p<0.05) upon increased RVP; however, it prevented the reduction in RVC entirely. Systemically, the RVP-induced decline in mean arterial pressure (MAP) was more pronounced in ANG II clamped animals vs. controls (−22.4±4.1 vs. −9.9±2.3mmHg, p<0.05), whereas the decrease in heart rate (HR) was less (−5±6bpm vs. −23±4bpm, p<0.05). In animals given vasopressin to maintain a comparable MAP after ACE inhibition (ACEi), increased RVP did not impact MAP and HR. RVC also did not change (0.018±0.008ml/minˑmmHg), and the reduction of GFR was no longer significant (−0.54±0.15ml/min). Furthermore, RBF autoregulation remained intact and was reset to a lower level when RVP was increased. In conclusion, RVP-induced renal vasoconstriction is attenuated when ANG II is clamped or inhibited. The systemic effect of increased RVP, a decrease in HR related to a mild decrease in blood pressure, is attenuated also during ANG II clamp. Last, RBF autoregulation remains intact when RVP is elevated and is reduced to lower levels of RBF. This suggests that in venous congestion, the intact RBF autoregulation could be partially responsible for the vasoconstriction.

Association of Noise Annoyance with Measured Renal Hemodynamic Changes

<b><i>Background:</i></b> Chronic mental stress is recognized as a modifiable risk factor for cardiovascular disease. The aim of this study was to demonstrate that noise annoyance-induced stress is associated with changes in renal hemodynamics. <b><i>Methods:</i></b> Renal hemodynamic parameters were measured using steady-state input clearance with infusion of para-aminohippuric acid and inulin in individuals with normal, high normal, and elevated blood pressure. All individuals ranked subjective annoyance due to noise in everyday life on a 7-grade Likert scale. The median of all rankings was used as a cutoff point to divide the group into noise-annoyed and non-noise-annoyed individuals. Different renal hemodynamic parameters were calculated based on the Gomez equation. <b><i>Results:</i></b> Noise-annoyed individuals (<i>n</i> = 58) showed lower renal plasma flow (599 ± 106 vs. 663 ± 124 mL/min, <i>p</i> = 0.009), lower renal blood flow (1,068 ± 203 vs. 1,172 ± 225 mL/min, <i>p</i> = 0.047), higher filtration fraction (22.7 ± 3.3 vs. 21.3 ± 3.0, <i>p</i> = 0.012), higher renal vascular resistance (88.9 ± 25.6 vs. 75.8 ± 22.9 mm Hg/[mL/min], <i>p</i> = 0.002), and higher resistance of afferent arteriole (2,439.5 ± 1,253.4 vs. 1,849.9 ± 1,242.0 dyn s⁻¹ cm⁻⁵, <i>p</i> = 0.001) compared to non-noise-annoyed individuals (<i>n</i> = 55). There was no difference in measured glomerular filtration rate (133 ± 11.8 vs. 138 ± 15 mL/min, <i>p</i> = 0.181), resistance of efferent arteriole (2,419.4 ± 472.2 vs. 2,245.8 ± 370.3 dyn s⁻¹ cm⁻⁵, <i>p</i> = 0.060), and intraglomerular pressure (64.0 ± 3.1 vs. 64.6 ± 3.5 mm Hg, <i>p</i> = 0.298) between the groups. After adjusting for age, renal plasma flow, renal blood flow, and renal vascular resistance remained significantly different between the groups, with a trend in increased afferent arteriolar resistance and filtration fraction. <b><i>Conclusion:</i></b> In this study, noise annoyance was associated with reduced renal perfusion attributed to increased renal vascular resistance predominantly at the afferent site. Long-term consequences of this renal hemodynamic pattern due to noise annoyance need to be investigated.

Abstract 12882: Renal Hemodynamics in Chronic Heart Failure With Preserved and Reduced Ejection Fraction

Introduction: Chronic heart failure (CHF) and impaired renal function are two co-existing medical conditions and known to be associated with adverse outcome. The cardiorenal interaction has not yet been analyzed thoroughly. The aim of this study was to assess renal and intraglomerular hemodynamics by constant infusion input clearance technique in subjects with CHF compared to healthy controls. Methods: This was a cross-sectional observational study including 85 subjects. The group of subjects with CHF consisted of 27 individuals with HFpEF and 27 individuals with HFrEF, who were compared to 31 controls. All subjects underwent renal clearance examination to determine measured -not estimated- glomerular filtration rate (GFR), renal blood and plasma flow (RBF, RPF) and to calculate renal hemodynamic parameters such as filtration fraction (FF), renal vascular resistance (RVR), intraglomerular pressure (P glom ) and resistances of the afferent (R A ) and efferent arterioles (R E ). Results: GFR was lower in subjects with CHF (88.6±13.1ml/min/1.73m 2 ) compared to controls (108.6±17. ml/min/1.73m 2 ) after adjustment for age and BP (p adj =0.037). There were no significant differences regarding RPF, RBF, FF, RVR, P glom , R A as well as R E after adjustment for age and BP. Similarly, there were no significant differences regarding renal hemodynamic parameters between HFpEF and HFrEF subjects. Bivariate correlation analysis in the group of subjects with CHF revealed an inverse association between NT-proBNP and RPF (R=-0.421, p=0.002), RBF (R=-0.414, p=0.002) and a positive association with FF (R=0.324, p=0.019), RVR (R=0.346, p=0.012) and R E (R=0.318, p=0.022). Conclusions: The findings of this study indicate that in CHF renal function is slightly reduced even though renal perfusion is preserved. With progressive severity of CHF as indicated by increasing NT-proBNP, renal vascular resistance in particular at the postglomerular side increases. Our data are in accordance with neuroendocrine activation in CHF since vasoconstriction at the postglomerular site points towards angiotensin II as mediator. The association between NT-proBNP and renal hemodynamics documents a close cardiorenal interaction in CHF.

P0002A NEW INSIGHT INTO THE MECHANISM OF HYPERCHLOREMIC METABOLIC ACIDOSIS IN KIDNEY TRANSPLANT RECIPIENTS: INCREASED POSTGLOMERULAR PERITUBULAR BLOOD FLOW IS A KEY CONDITION FOR THE DEVELOPEMENT OF CALCINEURIN INHIBITOR-INDUCED RENAL TUBULAR ACIDOSIS

Background and Aims Hyperchloremic metabolic acidosis (HCMA) due to renal tubular acidosis is a common complication in kidney transplant recipients(KTR). Potential renal dysfunction, rejection, ischemia, persistent hyperparathyroidism, calcineurin inhibitors (CNIs), etc. have been identified as causes but have not been fully proven, and whether HCMA is a determinant of poor graft prognosis in KTR is still controversial. The purpose of this study is to elucidate the actual mechanism of HCMA in KTR. Method HCMA was defined as follows: i) simple strong ion difference (SID) Na-CL, which is the most dominant metabolic factor in physicochemical approach for acid-base balance, is 34 or less, or â…±) the alkalizing drugs have been started after the KT to correct HCMA. And all the cases of having diarrhea from mycophenolate mofetil(MMF), and gastroenterocolitis from cytomegalovirus infection were excluded. The study group consisted of 47 KTRs who underwent living-kidney transplantation(KT) at our hospital as well as a control group of 43 of the matched donors. Among them, a total of 26 KTRs received the renal hemodynamic studies which were based on urinary clearance of inulin and para-aminohippuric acid 1year after KT. 1) The incidence of HCMA in KTR at 3 months(3m) and 1 year(1y) after KT were examined. 2) To elucidate factors related to HCMA in KTR at 1y, we comprehensively examined factors and compared HCMA groups with non-HCMA groups; donor and recipient background (gender, age, body size), immunological factors, information on transplant surgery, salt and protein intake, effective buffering factors for extracellular body fluids such as albumin and hemoglobin, serum calcium and phosphate concentrations and their ratios, administration of renin-angiotensin system inhibitors and diuretics,Tac trough level and Banff score of each histopathological lesion in 1y biopsy. As for the 26 KTRs who received the renal hemodynamic studies, glomerular filtration rate (GFR), renal plasma flow (RPF), filtration fraction(FF) (GFR/RPF) and pre-/post-glomerular vascular resistance (pre-/postVR) calculated from the Gomez' equations were also analyzed. Results 1) The incidence of HCMA in the KTR at 3m was 51% (24/47), which was much higher than the 6.9% (3/43) in those donors (p&lt;0.001), and the range of odds ratios (vs donor) adjusted by the background factors (age,gender, estimated GFR, albumin and hemoglobin) was 6.7-15.7 (p=0.0001-0.001). The incidence of HCMA in KTR at 1y decreased to 34%. 2)The univariate analysis of HCMA in KTR at 1y compared with non-HCMA showed an increase in RPF (p= 0.016), a decrease in post-VR (p= 0.003), and a decrease in FF (p= 0.0001), suggesting an increase in post-glomerular peritubular blood flow. In addition, the aah lesion score, an indicator of CNI vasculopathy, was also significantly higher in the HCMA (p = 0.015). There was no difference in Tac trough levels between HCMA and nonHCMA, and no independent factors were found by multivariate analysis. All cases with HCMA were classified into low post-VR (Fig.1). Furthermore, in low post-VR alone (n= 15), the Tac trough level at 1y was significantly higher in the HCMA (p= 0.002) (Fig.2). Conclusion In kidney transplant recipients, increased post-glomerular peritubular blood flow is a key condition for the development of CNI-induced renal tubular acidosis. The presence of HCMA suggests that it is probably not a serious condition, but rather a desirable hemodynamic state, however, more attention should be paid not to elevate CNI concentration levels in such conditions.