Richard P. E. van Dokkum

Microalbuminuria and Endothelial Dysfunction: Emerging Targets for Primary Prevention of End-organ Damage

A minor increase in urinary albumin excretion (microalbuminuria) is known to predict adverse renal and cardiovascular events in diabetic and hypertensive patients. Recent intriguing findings show that microalbuminuria is an early and sensitive marker of future cardiovascular events even in healthy subjects. The mechanisms linking microalbuminuria with end-organ damage have not been fully explained yet; however, generalized endothelial dysfunction might play an important role. Prevailing experimental and clinical data suggest that generalized endothelial dysfunction, frequently characterized by decreased nitric oxide bioavailability, actually precedes the development of microalbuminuria. This review summarizes the current knowledge about the intricate relationship between microalbuminuria and endothelial dysfunction. On the basis of the current evidence, we propose that microalbuminuria and endothelial dysfunction are an emerging target for primary prevention strategies in cardiovascular disease. In near future, dietary components improving nitric oxide bioavailability, such as cocoa-derived flavanols may play important role in these preventive strategies.

Altered renal hemodynamics and impaired myogenic responses in the fawn-hooded rat.

The present study examined whether an abnormality in the myogenic response of renal arterioles that impairs autoregulation of renal blood flow (RBF) and glomerular capillary pressure (PGC) contributes to the development of renal damage in fawn-hooded hypertensive (FHH) rats. Autoregulation of whole kidney, cortical, and medullary blood flow and PGC were compared in young (12 wk old) FHH and fawn-hooded low blood pressure (FHL) rats in volume-replete and volume-expanded conditions. Baseline RBF, cortical and medullary blood flow, and PGC were significantly greater in FHH than in FHL rats. Autoregulation of renal and cortical blood flow was significantly impaired in FHH rats compared with results obtained in FHL rats. Myogenically mediated autoregulation of PGC was significantly greater in FHL than in FHH rats. PGC rose from 46 +/- 1 to 71 +/- 2 mmHg in response to an increase in renal perfusion pressure from 100 to 150 mmHg in FHH rats, whereas it only increased from 39 +/- 2 to 53 +/- 1 mmHg in FHL rats. Isolated perfused renal interlobular arteries from FHL rats constricted by 10% in response to elevations in transmural pressure from 70 to 120 mmHg. In contrast, the diameter of vessels from FHH rats increased by 15%. These results indicate that the myogenic response of small renal arteries is altered in FHH rats, and this contributes to an impaired autoregulation of renal blood flow and elevations in PGC in this strain.The present study examined whether an abnormality in the myogenic response of renal arterioles that impairs autoregulation of renal blood flow (RBF) and glomerular capillary pressure (PGC) contributes to the development of renal damage in fawn-hooded hypertensive (FHH) rats. Autoregulation of whole kidney, cortical, and medullary blood flow and PGC were compared in young (12 wk old) FHH and fawn-hooded low blood pressure (FHL) rats in volume-replete and volume-expanded conditions. Baseline RBF, cortical and medullary blood flow, and PGCwere significantly greater in FHH than in FHL rats. Autoregulation of renal and cortical blood flow was significantly impaired in FHH rats compared with results obtained in FHL rats. Myogenically mediated autoregulation of PGC was significantly greater in FHL than in FHH rats. PGC rose from 46 ± 1 to 71 ± 2 mmHg in response to an increase in renal perfusion pressure from 100 to 150 mmHg in FHH rats, whereas it only increased from 39 ± 2 to 53 ± 1 mmHg in FHL rats. Isolated perfused renal interlobular arteries from FHL rats constricted by 10% in response to elevations in transmural pressure from 70 to 120 mmHg. In contrast, the diameter of vessels from FHH rats increased by 15%. These results indicate that the myogenic response of small renal arteries is altered in FHH rats, and this contributes to an impaired autoregulation of renal blood flow and elevations in PGC in this strain.

Myocardial Infarction Enhances Progressive Renal Damage in an Experimental Model for Cardio-Renal Interaction

Studied were the effects of myocardial infarction (MI) on mild renal function loss in unilateral nephrectomized (UnX) rats. UnX was performed, followed after 1 wk by a variable MI (UnX + MI; n = 24). Rats with only UnX (n = 15) or MI (n = 9) and double sham animals (CON, n = 15) served as controls. Renal outcome was measured by proteinuria and plasma creatinine. Focal glomerulosclerosis (FGS) incidence was evaluated by renal histology. Cardiac function and systolic BP were measured. A division into small and large infarcts after UnX was made a priori, resulting in two groups, one with a mild MI (<20%; n = 15) and one with a moderate MI (>20%; n = 9). Mild proteinuria up to 55.5 mg/d was observed in the UnX + mild MI group, whereas proteinuria rose significantly higher to 124.5 mg/d in the UnX + moderate MI group. Incidence of FGS was significantly increased in both UnX + MI groups compared with all other groups. The average MI size was 18%, 17%, and 25% in the MI, UnX + mild MI, and UnX + moderate MI group, respectively. LVP in both UnX + MI groups was correlated with proteinuria, indicative of a cardio-renal interaction. Clinically, these data imply that more patients are at risk for cardiovascular events and that after such an event, their chance of more renal function loss increases. Finding the underlying mechanism will enable improved protection for both kidneys and heart.

Endothelial Dilatory Function Predicts Individual Susceptibility to Renal Damage in the 5/6 Nephrectomized Rat

In experimental animal models of renal disease the degree of renal damage varies between individuals. This could be caused by variation in the noxious event or by differences in individual susceptibility. Intact endothelial function is assumed to provide a defense mechanism against progressive renal damage. This study hypothesized that interindividual differences in renal endothelial function might be involved in individual susceptibility to renal damage, and it investigated whether endothelial function of small renal arteries before induction of 5/6 nephrectomy (5/6 Nx) in rats was related to development of renal damage after 5/6 Nx. Wistar rats underwent 5/6 Nx, and small renal arteries of the removed right kidney were investigated for endothelium-dependent relaxation to acetylcholine (ACh, 10(-8) to 10(-4) mol/L). The contribution of underlying endothelial dilative mediators, NO, prostaglandins (PG), and endothelium-derived hyperpolarizing factor (EDHF), was assessed using the inhibitors, L-NMMA, indomethacin, and charybdotoxin+apamin, respectively. After 5/6 Nx, proteinuria developed in each rat ranging from 22 to 278 (84 +/- 14) mg/24 h at week 5 (n = 23). Interestingly, a significant inverse correlation between individual ACh-relaxation (expressed as area under curve in arbitrary units) and proteinuria 5 wk after 5/6 Nx was found (r = -0.54; P = 0.008; n = 23). An inverse correlation was also found between individual NO contribution as well as PG contribution and proteinuria 5 wk after 5/6 Nx (r = -0.86, P = 0.001, n = 11; and r = -0.74, P = 0.01, n = 11, respectively). In addition, individual ACh-relaxation was positively correlated with GFR measured 6 wk after 5/6 Nx (r = 0.58; P = 0.016; n = 17). This study demonstrates for the first time that individual renal endothelial dilatory function of the healthy rat predicts susceptibility to renal damage after 5/6 Nx, which seems to depend on individual endothelial NO and PG activity.

Impaired autoregulation of renal blood flow in the fawn-hooded rat

The responses to changes in renal perfusion pressure (RPP) were compared in 12-wk-old fawn-hooded hypertensive (FHH), fawn-hooded low blood pressure (FHL), and August Copenhagen Irish (ACI) rats to determine whether autoregulation of renal blood flow (RBF) is altered in the FHH rat. Mean arterial pressure was significantly higher in conscious, chronically instrumented FHH rats than in FHL rats (121 +/- 4 vs. 109 +/- 6 mmHg). Baseline arterial pressures measured in ketamine-Inactin-anesthetized rats averaged 147 +/- 2 mmHg (n = 9) in FHH, 132 +/- 2 mmHg (n = 10) in FHL, and 123 +/- 4 mmHg (n = 9) in ACI rats. Baseline RBF was significantly higher in FHH than in FHL and ACI rats and averaged 9.6 +/- 0.7, 7.4 +/- 0.5, and 7.8 +/- 0.9 ml. min-1. g kidney wt-1, respectively. RBF was autoregulated in ACI and FHL but not in FHH rats. Autoregulatory indexes in the range of RPPs from 100 to 150 mmHg averaged 0.96 +/- 0.12 in FHH vs. 0.42 +/- 0.04 in FHL and 0.30 +/- 0.02 in ACI rats. Glomerular filtration rate was 20-30% higher in FHH than in FHL and ACI rats. Elevations in RPP from 100 to 150 mmHg increased urinary protein excretion in FHH rats from 27 +/- 2 to 87 +/- 3 microg/min, whereas it was not significantly altered in FHL or ACI rats. The percentage of glomeruli exhibiting histological evidence of injury was not significantly different in the three strains of rats. These results indicate that autoregulation of RBF is impaired in FHH rats before the development of glomerulosclerosis and suggest that an abnormality in the control of renal vascular resistance may contribute to the development of proteinuria and renal failure in this strain of rats.

The role of angiotensin(1-7) in renal vasculature of the rat

Objective Angiotensin(1–7) is an active component of the renin–angiotensin–aldosterone system. Its exact role in renal vascular function is unclear. We therefore studied the effects of angiotensin(1–7) on the renal vasculature in vitro and in vivo. Methods Isolated small renal arteries were studied in an arteriograph system by constructing concentration–response curves to angiotensin II, without and with angiotensin(1–7). In isolated perfused kidneys, the response of angiotensin II on renal vascular resistance was measured without and with angiotensin(1–7). The influence of angiotensin(1–7) on angiotensin II-induced glomerular afferent and efferent constriction was assessed with intravital microscopy in vivo under anaesthesia. In freely moving rats, we studied the effect of angiotensin(1–7) on angiotensin II-induced reduction of renal blood flow with an electromagnetic flow probe. Results Angiotensin(1–7) alone had no effect on the renal vasculature in any of the experiments. In vitro, angiotensin(1–7) antagonized angiotensin-II-induced constriction of isolated renal arteries (9.71 ± 1.21 and 3.20 ± 0.57%, for control and angiotensin(1–7) pre-treated arteries, respectively; P < 0.0005). In isolated perfused kidneys, angiotensin(1–7) reduced the angiotensin II response (100 ± 16.6 versus 72.6 ± 15.6%, P < 0.05) and shifted the angiotensin II dose–response curve rightward (pEC50, 6.69 ± 0.19 and 6.26 ± 0.12 for control and angiotensin(1–7) pre-treated kidneys, respectively; P < 0.05). Angiotensin(1–7), however, was devoid of effects on angiotensin-II-induced constriction of glomerular afferent and efferent arterioles and on angiotensin-II-induced renal blood flow reduction in freely moving rats in vivo. Conclusion Angiotensin(1–7) antagonizes angiotensin II in renal vessels in vitro, but does not appear to have a major function in normal physiological regulation of renal vascular function in vivo.

Renal vascular dysfunction precedes the development of renal damage in the hypertensive Fawn-Hooded rat

It is unknown whether generalized vascular dysfunction precedes the development of kidney disease. Therefore, we studied myogenic constriction and endothelium-mediated dilatory responses in two inbred Fawn-Hooded (FH) rat strains, one of which spontaneously develops hypertension, proteinuria, and glomerulosclerosis (FHH), whereas the other (FHL) does not. Small renal, mesenteric resistance arteries and thoracic aorta isolated from FH rats before (7 wk old) and after the development of mild proteinuria (12 wks old) were mounted in perfused and isometric set-ups, respectively. Myogenic response, endothelium-dependent relaxation, and the contribution of endothelium-mediated dilatory compounds were studied using their respective inhibitors. Myogenic reactivity was assessed constructing pressure-diameter curves in the presence and absence of calcium. At the age of 7 wk, renal arteries isolated from kidneys of FHH rats developed significantly lower myogenic tone compared with FHL, most likely because of excessive cyclo-oxygenase 1-mediated production of constrictive prostaglandins. Consequently, young FHH demonstrated reduced maximal myogenic tone (22 +/- 4.8 vs. 10.8 +/- 2.0%, P = 0.03) and the peak myogenic index (-6.9 +/- 4.8 vs. 0.6 +/- 0.8%/mmHg, P = 0.07 for FHL vs. FHH, respectively). Active myogenic curves obtained in mesenteric arteries isolated from 7-wk-old rats did not differ between either strain, demonstrating a similar level of systemic myogenic tone in FHL and FHH rats. Therefore, before any renal end-organ damage is present, myogenic response seems selectively impaired in renal vasculature of FHH rats. Aortic reactivity did not differ between FHL and FHH at the time points studied. The present study shows that vascular dysfunction in both small renal and systemic arteries precedes renal end-organ damage in a spontaneous model of hypertension-associated renal damage. These early vascular changes might be potentially involved in the increased susceptibility of FHH rats to renal injury.

Altered myogenic constriction and endothelium-derived hyperpolarizing factor-mediated relaxation in small mesenteric arteries of hypertensive subtotally nephrectomized rats

Objectives Chronic renal failure (CRF) is associated with altered systemic arterial tone and hypertension. Myogenic constriction and endothelium-derived hyperpolarizing factor (EDHF)-dependent relaxation represent major vasoregulatory mechanisms in small systemic arteries. Elevated myogenic response and impaired EDHF might participate in the development of essential hypertension; however, their role in CRF-related hypertension is unknown. We investigated whether myogenic response and EDHF are altered in subtotally nephrectomized (sNX) rats and whether these changes are modifiable by chronic treatment with angiotensin-converting enzyme (ACE) inhibitor. Methods In a pressure arteriograph, myogenic constriction and EDHF-mediated relaxation were evaluated in small mesenteric arteries isolated from male Wistar rats 15 weeks after either sham operation (n = 7) (SHAM), sNX (n = 12) or sNX followed by 9 weeks of treatment with lisinopril (sNX + LIS, 2.5 mg/kg, n = 13). Results Surprisingly, myogenic response was reduced in hypertensive CRF rats (maximal myogenic tone: 37 ± 2 and 18 ± 4%, P < 0.01; peak myogenic index: −0.80 ± 0.08 and −0.40 ± 0.12%/mmHg, P < 0.05 in SHAM and sNX respectively). At the same time EDHF-mediated relaxation was also impaired (maximal response: 92 ± 2 and 77 ± 5%, P < 0.01; pD2: 6.5 ± 0.1 and 5.9 ± 0.1, P < 0.05). Both myogenic response and EDHF were inversely related to the severity of renal failure and restored by treatment with lisinopril to levels found in SHAM animals. Conclusion Major constrictive (myogenic) and dilatory (EDHF) mechanisms of small systemic arteries are impaired in hypertensive CRF rats. These alterations do not seem to participate in the development of hypertension, being rather directly related to the severity of renal impairment. Both systemic vascular changes might be restored by renoprotective treatment with ACE inhibitor.

Myocardial infarction does not further impair renal damage in 5/6 nephrectomized rats

BACKGROUND Recent observational studies show that reduced renal function is an independent risk factor for the development of cardiovascular disease. Previously, we reported that myocardial infarction (MI) indeed enhanced mild renal function decline in rats after unilateral nephrectomy (NX) and that RAAS intervention inhibited this decline. The effects of an MI on pre-existing severe renal function loss and the effects of RAAS intervention interrupting this hypothesized cardiorenal interaction are however unknown and clinically even more relevant. METHODS Male Wistar rats underwent MI, sham MI, 5/6NX, or 5/6NX and MI. Six weeks later, the NX rats were treated with an angiotensin-converting enzyme inhibitor (ACEi) or vehicle for 6 weeks. RESULTS An MI did not significantly induce more proteinuria (303 +/- 46 versus 265 +/- 24 mg/24 h) and glomerulosclerosis (40 +/- 11 versus 28 +/- 4 arbitrary units) in 5/6NX+MI compared to 5/6NX, and ACEi therapy was equally effective in reducing renal damage in these groups. In the 5/6NX+MI group, decreased renal blood flow and creatinine clearance were observed compared to 5/6NX (2.2 +/- 0.6 versus 3.6 +/- 0.4 ml/min/kg and 2.1 +/- 0.3 versus 2.9 +/- 0.3 ml/min/kg), which both increased after ACEi to levels comparable found in the group that underwent 5/6NX alone. CONCLUSIONS MI does not further deteriorate structural renal damage induced by 5/6NX compared with 5/6NX alone. Furthermore, renal haemodynamic impairment occurs after MI, which can be improved applying ACEi therapy. Therefore, we conclude that treatment with ACEi should be optimized in patients with chronic kidney disease after MI to improve renal function.

Difference in Susceptibility of Developing Renal Damage in Normotensive Fawn-Hooded (FHL) and August × Copenhagen Irish (ACI) Rats After Nω-Nitro-l-arginine Methyl Ester Induced Hypertension ☆

Previous studies using the fawn-hooded hypertensive (FHH) rat have indicated that genetic factors appear to be important in determining the susceptibility to develop renal damage. This was further investigated by comparing the effects of N(omega)-nitro-L-arginine methyl ester (L-NAME) induced hypertension on functional and structural renal damage in two normotensive strains, the resistant August x Copenhagen Irish rat (ACI) and the normotensive fawn-hooded (FHL) rat, which also appears to carry a susceptibility locus for renal failure. Male rats were studied during chronic treatment with L-NAME in either a low dose (LD, 75 to 100 mg/L drinking fluid) or a high dose (HD, 175 to 250 mg/L). Survival of FHL rats was adversely affected by L-NAME treatment. All FHL-HD and 6 of 14 FHL-LD rats died before the end of the 11 weeks of follow-up, whereas all treated ACI rats except for one ACI-HD animal survived. In both strains, L-NAME caused a dose dependent increase in systolic blood pressure (SBP). However, at similar levels of SBP, the increase in albuminuria (UaV) was significantly higher in FHL compared with ACI, as was the incidence of glomerulosclerosis (GS). Both the SBP and the blood pressure burden (SBP-Av), defined as SBP averaged over the period of follow-up, directly correlated with UaV and GS in both strains. However, the increase in the degree of renal damage per millimeter of mercury increase in SBP or SBP-Av was significantly higher in the FHL than in the ACI rats. Our findings clearly show that FHL rats are more susceptible to developing renal damage after induction of hypertension by chronic L-NAME treatment. We conclude that there is an interaction between blood pressure and the genetic susceptibility to renal disease in the FHL rat.