Iris Kingma

Effects of losartan and captopril on endothelin-1 production in blood vessels and glomeruli of rats with reduced renal mass.

Recently, we have reported that endothelin-1 (ET-1) production is increased in blood vessels and glomeruli of rats with chronic renal failure. This study was design to investigate the role of angiotensin II (Ang II) in endogenous ET-1 production in rats with reduced renal mass. One week after subtotal (5/6) nephrectomy, uremic rats were divided into three groups, and received either no treatment, the Ang II subtype 1 receptor (AT1) antagonist losartan (10 mg/kg/day), or the angiotensin-converting enzyme inhibitor (ACE-I) captopril (30 mg/kg/day) for 6 weeks. Sham-operated rats were used as controls and received no treatment. The levels of immunoreactive ET-1 (ir-ET-1) in plasma and urine, as well as in vascular and renal tissues, were determined by radioimmunoassay (RIA) after extraction. In uremic rats, losartan and captopril completely prevented the increase in systolic blood pressure. At week 6, plasma ir-ET-1 was similar in the different groups of uremic rats and in the controls. However, ir-ET-1 concentration in the mesenteric arterial bed, the thoracic aorta, preglomerular arteries, and glomeruli, as well as urinary ir-ET-1 excretion were significantly greater in uremic-untreated rats compared to controls (P < .01). Treatment of uremic rats with losartan or captopril reduced irET-1 concentration in the thoracic aorta and preglomerular arteries (P < .05), but ir-ET-1 concentration in the mesenteric arterial bed was unchanged. Although both drugs completely prevented the increase in proteinuria, losartan but not captopril significantly reduced ir-ET-1 concentration in glomeruli (P < .05) and normalized urinary ir-ET-1 excretion. This indicates that increased ET-1 production in blood vessels and glomeruli of uremic rats is modulated, at least in part, by Ang II through the AT1 receptor. The beneficial effects of the AT1 antagonist losartan could be attributable to the attenuation of Ang II-induced ET-1 production in this rat remnant kidney model of chronic renal failure, whereas those of the ACE-I captopril are not related to changes in ET-1 production in glomeruli.

Plasma endothelin levels and blood pressure in hemodialysis and in CAPD patients. Effect of subcutaneous erythropoietin replacement therapy.

We investigated plasma endothelin (ET) concentration and blood pressure in 44 patients with end stage renal failure chronically treated with either hemodialysis (n = 24) or continuous ambulatory peritoneal dialysis (CAPD) (n = 20). Half of the subjects were on chronic erythropoietin (r-HuEPO) replacement therapy (30-60 U/kg) subcutaneously, 3 times weekly. The mean plasma ET level of the whole group was about five fold higher than the normal range. Plasma ET concentration and mean blood pressure were higher in hemodialysis than in CAPD patients (33.3 +/- 2.1 vs 24.8 +/- 1.2 pg/ml, p < 0.01, and 101 +/- 2.4 vs 91 +/- 3 mmHg, p < 0.025). There was a significant correlation between plasma ET levels and systolic blood pressures in both groups (r = 0.45, p < 0.05). Patients (hemodialysis and CAPD) receiving subcutaneous r-HuEPO had higher mean blood pressure (99 +/- 3 vs 85 +/- 4 mmHg, p < 0.01), while their plasma ET levels were similar to untreated patients independent of the dialysis mode. However, a statistically significant correlation between plasma ET and systolic blood pressure was present only in the r-HuEPO treated group (r = 0.46, p < 0.05 vs r = 0.29, N.S., for the untreated group). These results show that plasma ET levels are markedly increased on both dialysis mode, but the values are lower in CAPD patients. Plasma ET concentrations significantly correlated with systolic blood pressures in the whole group of patients, and also in those receiving r-HuEPO replacement therapy.

Increased Immunoreactive Endothelin-1 Levels in Blood Vessels and Glomeruli of Rats with Reduced Renal Mass

Elevated plasma and urinary endothelin-1 (ET-1) levels have been reported in patients with renal failure as well as in remnant kidney models of chronic renal failure. We investigated whether these changes are related to increased ET-1 production in cardiovascular and renal tissues of rats with reduced renal mass. In uremic rats, systolic blood pressure rose in parallel with the progression of renal insufficiency. At week 6, changes in systolic blood pressure were positively correlated with serum creatinine levels (r = 0.728, p < 0.01). Plasma immunoreactive ET-1 (ir-ET-1) concentration was similar in uremic rats and sham-operated controls. In contrast, urinary ir-ET-1 excretion was significantly greater in uremic rats and was correlated with the elevation of serum creatinine and proteinuria (r = 0.795, and 0.922, p < 0.01, respectively). Compared to the controls, ir-ET-1 concentration in the thoracic aorta, preglomerular arteries and glomeruli were 1.4-, 3.5- and 6.7-fold higher, respectively, in uremic rats (p < 0.01) than in the controls. However, ir-ET-1 concentration in the mesenteric arterial bed and the left ventricle remained similar in the 2 groups, whereas it was significantly lower in the renal papilla of uremic rats (p < 0.01). Thus, ET-1 production is unchanged or slightly increased in extrarenal cardiovascular tissues of rats with reduced renal mass. In contrast, ET-1 production is significantly augmented in preglomerular arteries and glomeruli, but reduced in the papilla, suggesting that increased urinary ir-ET-1 excretion in uremic rats reflects ET-1 overproduction in the former renal tissues. Elevated ET-1 production in blood vessels and glomeruli may thus play a key role in the aggravation of hypertension and the progression of renal insufficiency in this rat remnant kidney model of chronic renal failure.

Influence of Acute Renal Failure on Coronary Vasoregulation in Dogs

Impaired renal function is associated with an increased risk for cardiovascular events and death, but the pathophysiology is poorly defined. The hypothesis that coronary blood flow regulation and distribution of ventricular blood flow could be compromised during acute renal failure (ARF) was tested. In two separate groups (n = 14 each) of dogs with ARF, (1) coronary autoregulation (pressure-flow relations), vascular reserve (reactive hyperemia), and myocardial blood flow distribution (microspheres) and (2) coronary vessel responses to intracoronary infusion of select endothelium-dependent and -independent vasodilators were evaluated. In addition, coronary pressure-flow relations and vascular reserve after inhibition of nitric oxide and prostaglandin release were evaluated. Under resting conditions, myocardial oxygen consumption increased in dogs with ARF compared with no renal failure (NRF; 11.8 +/- 9.2 versus 5.0 +/- 1.5 ml O(2)/min per 100 g; P = 0.01), and the autoregulatory break point of the coronary pressure-flow relation was shifted to higher diastolic coronary pressures (60 +/- 17 versus 52 +/- 8 mmHg in NRF; P = 0.003); the latter was shifted further rightward after inhibition of both nitric oxide and prostaglandin release. The endocardial/epicardial blood flow ratio was comparable for both groups, suggesting preserved ventricular distribution of blood flow. In dogs with ARF, coronary vascular conductance also was reduced (P = 0.001 versus NRF), but coronary zero-flow pressure was unchanged. Vessel reactivity to each endothelium-dependent/independent compound also was blunted significantly. In conclusion, under resting conditions, coronary vascular tone, reserve, and vessel reactivity are markedly diminished with ARF, suggesting impaired vascular function. Consequently, during ARF, small increases in myocardial oxygen demand would induce subendocardial ischemia as a result of a limited capacity to increase oxygen supply and thereby contribute to higher risk for adverse coronary events and mortality.

CHRONIC NITRIC OXIDE INHIBITION AGGRAVATES HYPERTENSION IN ERYTHROPOIETIN-TREATED RENAL FAILURE RATS

Alterations in nitric oxide (NO) and endothelin-1 (ET-1) production have recently been reported in erythropoietin (r-HuEPO)-induced hypertension in renal failure rats. The present study was designed to evaluate the effect of NO synthase inhibition with the L-arginine analog NG-nitro-L-arginine methyl ester (L-NAME) on blood pressure (BP) and ET-1 production in control and in uremic rats treated or not treated with r-HuEPO. Renal failure was induced by a two-stage 5/6 nephrectomy. Control and uremic rats were studied separately and subdivided into four groups: vehicle, r-HuEPO, L-NAME + vehicle and L-NAME + r-HuEPO. L-NAME (100 mg/kg/day), r-HuEPO (100 U/kg, subcutaneously, three times per week), the vehicle or both were administered during 4 weeks in control rats and during 2 weeks in uremic rats. Systolic BP was recorded before and after the onset of treatment at weeks 2 and 4 in control rats and at weeks 1 and 2 in uremic rats. Hematocrit, serum creatinine, plasma, blood vessel (thoracic aorta and mesenteric artery bed) and renal cortex immunoreactive (ir) ET-1 concentrations were measured at the end of the protocol. L-NAME enhanced BP in control and uremic rats and the increase was significantly higher in uremic rats under r-HuEPO therapy (222 ± 7 mmHg vs 198 ± 6 mmHg, p<0.05). L-NAME induced an increase in thoracic aorta ir-ET-1 concentrations in control and uremic rats. In contrast, ir-ET-1 concentrations were unchanged in the mesenteric arterial bed and the renal cortex of control and uremic animals. R-HuEPO increased thoracic aorta ir-ET-1 contents in L-NAME treated control and uremic rats. These results underline the important role of NO release in opposing the action of vasopressors on blood vessel tone which appears more important in uremic rats treated with r-HuEPO. L-NAME treatment increased large vessel, but not small resistance artery ir-ET-1 concentrations, suggesting differential regulation of ET-1 production in different vascular beds under chronic NO synthase inhibition.

Uremia enhances the blood pressure response to erythropoietin.

To investigate the role of uremia in the development of human recombinant erythropoietin (r-HuEPO)-induced hypertension, Wistar rats were divided into a uremic (subtotal nephrectomy) and a control group. After three weeks, both groups were again divided and each subgroup received either r-HuEPO (100 u/kg s.c., 3 times weekly) or the vehicle for a further 3 weeks. Hematocrit, blood pressure and blood chemistry were measured prior to surgery, before either vehicle or r-HuEPO treatment and before euthanasia. The uremic group developed anemia, hypertension and all the biochemical features observed in humans with end-stage renal disease. r-HuEPO therapy increased hematocrit from 29 +/- 2.5% to 46 +/- 2% (p < 0.01) in the uremic rats. The mean baseline blood pressure was 119 +/- 10 mmHg. At week 3, mean blood pressure was unchanged in control rats, but it was increased to 151 +/- 5 mmHg (p < 0.01) in the nephrectomized group. At week 6, mean blood pressure in the untreated uremic rats remained unchanged from week 3, but blood pressure in the uremic animals treated with r-HuEPO increased significantly to 187 +/- 8 mmHg (p < 0.01). There was no significant correlation between hematocrit and blood pressure in the r-HuEPO treated uremic group (r = 0.01, NS). r-HuEPO had no effect on blood pressure in control rats despite a significant increase in hematocrit. These results indicate that the blood pressure response to r-HuEPO is enhanced in rats with chronic renal failure.

Plasma and Blood Vessel Endothelin-1 Concentrations in Hypertensive Uremic Rats Treated with Erythropoietin

The present study was designed to evaluate whether changes in plasma and blood vessel endothelin-1 (ET-1) concentrations may play a role in the enhanced blood pressure response to recombinant human erythropoietin (r-HuEPO) replacement therapy in uremia. Renal failure was induced by 5/6 nephrectomy (Nx). Uremic rats received either r-HuEPO (100 u s.c. three times a week) or the vehicle for 5 weeks. They were compared to control rats receiving the vehicle. Systolic blood pressure (tail cuff method), hematocrit, serum creatinine, plasma and tissue ET-1 were measured at the end of the protocol. Immunoreactive ET-1 (ir-ET-1) was determined by radioimmunoassay of acid-extracts from the plasma, thoracic aorta and mesenteric arterial bed. Creatinine increased about three fold in Nx animals. Blood pressure in control rats was 120+/-3 mmHg compared to 161 +/-6 mmHg in the Nx + vehicle group (p <0.01) and 199+/-9 mmHg in the Nx + r-HuEPO group (p <0.01 vs Nx + vehicle). Hematocrit in control rats was 41.3+/-0.4% vs 32.6+/-1.8% in the Nx + vehicle group (p <0.01) and 47.6+/-1.5% in the Nx + r-HuEPO group (p <0.01). Plasma ir-ET-1 levels were similar in the Nx + vehicle and Nx + r-HuEPO groups (7.9+/-1.0 and 7.8+/-0.8 pg/ml). In contrast, thoracic aorta ir-ET-1 content was significantly higher in the Nx + r-HuEPO group than in the Nx + vehicle group (20.3+/-2.9 vs 13.4+/-1.9 pg, p <0.05). Similar results were obtained in the mesenteric arterial bed. There were significant correlations between blood pressure and ir-ET-1 content in the thoracic aorta (r= 0.45, p<0.05) and in the mesenteric arterial bed (r= 0.41, p<0.05). Vascular ET-1 content but not plasma levels are increased in uremic rats treated with r-HuEPO suggesting an increase in blood vessel ET-1 production which may play a role in the pathogenesis of r-HuEPO-induced hypertension.