Volume 3, Number 1, March 2002

POPULAR
TOPICPAPERInteraction of ACE inhibitors and AT₁-receptor blockers on maximum blood pressure response in spontaneous hypertensive rats
Trefor Morgan, Cory Griffiths, Lea Delbridge

This study in spontaneous hypertensive rats (SHR) was designed to determine whether a greater fall in blood pressure (BP) could be achieved with the combination of an angiotensin-converting enzyme inhibitor (ACE-I) and an AT₁-receptor blocking drug than with higher doses of either drug alone.
The peak effect of captopril occurred 3–4 hours post-dose and a plateau response was achieved with 10 mg/kg. The peak effect of losartan occurred 7–8 hours post-dose and a plateau response was achieved with 10 mg/kg. Increasing the dose of either drug caused no greater fall in BP, but increased the duration of the effect.
Captopril, 10 mg/kg, administered with losartan 10 mg/kg caused a greater fall in BP than captopril or losartan, 20 mg/kg. This was present after acute doses or after one week of daily therapy.
The combination of ACE-I and AT₁-blocking drugs is more effective than either therapy alone and may be a useful combination to manage hypertension and/or cardiac failure.

JRAAS 2002;3:16-18.

POPULAR
TOPICPAPERHyperglycaemia-induced intrarenal RAS activation: the contribution of metabolic pathways
M Cecilia Lansang, Suzette Y Osei, Caroline Coletti, Janelle Krupinski, Norman K Hollenberg

Hyperglycaemia-induced activation of the renin-angiotensin system (RAS) has been observed in normal and diabetic humans. Our main objective was to determine whether the mechanism involved a physical or metabolic effect of glucose. First, Sprague-Dawley rats of the CD strain were given sequential intravenous (i.v.) doses of 0.01, 0.1, 1.0, and 3.0 mg/kg candesartan 30 minutes apart, in the presence of a continuous i.v. infusion of dextrose 20% in water (D20W). The 0.1 mg/kg dose produced a maximal renal blood flow (RBF) response and was used thereafter. Another set of animals then received an infusion of either normal saline (NS), dextrose 5% in water (D5W) or dextrose 20% in water (D20W) for 2 hours, followed by candesartan 0.1 mg/kg i.v. Finally, the response to candesartan 0.1 mg/kg i.v. during D20W infusion was compared with that during infusion of 2-deoxyglucose (2DG), a glucose analogue that competitively inhibits the glycolytic enzyme, hexokinase. RBF (electromagnetic flowmeter), blood pressure (BP), blood glucose, and urine glucose were monitored. There was no significant RBF response to candesartan on either NS (6.01±0.48 to 6.20±0.49 ml/minute/g kidney; p=0.216) or D5W (7.63±1.20 to 7.58±1.39 ml/minute/g kidney; p=0.965), whereas there was a significant response to D20W (6.64±0.59 to 7.46±0.67 ml/minute/g kidney; p=0.002). The RBF response was significantly enhanced by D20W compared with 2DG (change in RBF: 0.82±0.22 vs. -0.04±0.26; p=0.05), despite similar BP, blood glucose, and urine glucose. Glucose acts, at least in part, through intracellular utilisation to induce RAS activation, as manifested by an enhanced renal vascular response to an angiotensin II antagonist.

JRAAS 2002;3:19-23.

PAPEROxidative stress increases the expression of the angiotensin-II receptor type 1 in mouse peritoneal macrophages
Shlomo Keidar, Ronit Heinrich, Marielle Kaplan, Michael Aviram

Angiotensin II (Ang II) has been shown to accelerate atherogenesis, and the cellular Ang II type 1 (AT₁)-receptor mediates most of Ang II-induced pro-atherogenic effects. In this study we have examined the effect of macrophage oxidative stress on cellular AT₁-receptor expression.
Mouse peritoneal macrophages (MPM) from apolipoprotein-E deficient (E⁰) mice at increasing ages (1–6 months) demonstrated an age-dependent increase in cellular lipid-peroxides (PD) content. In parallel, the AT₁-receptor mRNA and protein levels both increased by up to 3.7-fold and 1.7-fold, respectively, in MPM from 6-month old mice compared with 1-month old mice. Vitamin E supplementation to E⁰ mice significantly decreased the MPM PD content and macrophage AT₁-receptor mRNA expression compared with placebo-treated mice. The role of oxidative stress in the cellular expression of AT₁-receptors was further demonstrated by manipulation of macrophage glutathione content. Buthionine-sulfoximine, a glutathione synthesis inhibitor, increased MPM PD content and AT₁-receptor mRNA expression, whereas L-2-oxothiazolidine-4-carboxylic acid, that contributes to glutathione synthesis, reduced macrophage PD and AT₁-receptor mRNA expression. Incubation of MPM with oxidised low-density lipoproteins (LDL) led to a significant, dose-dependent and time-dependent increase in macrophage AT₁-receptor mRNA and protein expression, compared with control cells. In contrast, native LDL or acetylated LDL did not significantly affect macrophage AT₁-receptor mRNA expression.
In conclusion, our findings suggest that oxidative stress in macrophages induces AT₁-receptor expression. This phenomenon can stimulate the interaction of Ang II with macrophages and hence accelerate macrophage foam cell formation and early atherogenesis.

JRAAS 2002;3:24-30.

PAPERComparative effects of cilazapril, carvedilol and their combination in preventing from left ventricular remodelling after acute myocardial infarction in rats
Yuejin Yang, Yida Tang, Yingmao Ruan, Yongli Li, Yanwen Zhou, Runlin Gao, Jilin Chen, Zaijia Chen

Objectives: To compare the effects of cilazapril, carvedilol and their combination in preventing left ventricular remodelling (LVRM) after acute myocardial infarction (AMI) in rats.
Methods: Twenty-four hours after left coronary artery ligation, 100 surviving AMI female Sprague-Dawley rats were randomly assigned to: (1) AMI control (n=25); (2) cilazapril (Cila, 1 mg/kg/day) (n=25); (3) carvedilol (Car, 1 mg/kg/day) (n=25), and (4) cilazapril (1 mg/kg/day)+ carvedilol (1 mg/kg/day) (combination) (n=25) groups. A sham-operated group (n=17) was selected randomly as a non-infarction control. After four weeks of therapy with the drugs given by gastric gavage, haemodynamic studies were performed, following which the rat hearts were fixed and pathologically analysed. Rats with MI size <35% or >55% were excluded. Complete data were obtained in 64 rats, comprising AMI control (n=13), Cila (n=12), Car (n=12), Combination (n=14), and sham-operated (n=13) groups.
Results: There were no significant differences in MI size between the four AMI groups (45.2–46.7%, p>0.05). Compared with the sham-operated group, left ventricular (LV) end diastolic pressure (LVEDP), volume (LVV), weight (LVW), septal thickness (STh) and right ventricular weight (RVW) were all significantly increased (all p<0.001) in the AMI group, while the LV pressure maximal rate of rise and fall (±dp/dt) was significantly decreased (all p<0.001). In comparison with the AMI group, LVEDP, LVV, LVW, STh and RVW were all significantly decreased, while ±dp/dt was significantly increased in the Cila, Car, and combination groups, with LVEDP and STh decreasing more in the combination group than in the two monotherapy groups (p<0.05–0.01). There were no significant differences in other variables between the three therapy groups.
Conclusions: Cilazapril, carvedilol and their combination are all effective in preventing LVRM after AMI in rats, and in improving haemodynamics and LV function, with the combination therapy being superior to monotherapy in all respects.

JRAAS 2002;3:31-35.

PAPERForearm vasodilator response to angiotensin II in elderly women receiving candesartan: role of AT₂- receptors
Stephen Phoon, Laurence Guy Howes

The effects of angiotensin II (Ang II) and the Ang II type 2 (AT₂) receptor antagonist, PD 123319, on forearm vascular resistance (FVR) were studied in elderly women during Ang II type 1 (AT₁) receptor antagonist therapy. Eight women, aged 67±6 years, received the AT₁-receptor antagonist, candesartan, 8–16 mg once-daily for three weeks. FVR responses to intra-brachial arterial infusions of Ang II (8–32 ng/minute) during the co-infusion of PD 123319 (8 µg/minute) or placebo were measured at the end of the second and third weeks in a randomised, double-blind, crossover study.
Ang II produced dose-dependent reductions in FVR during both the placebo and PD 123319 infusions. However, FVR was significantly higher during PD 123319 infusions than during placebo infusions. Candesartan therapy unmasks a vasodilator response to Ang II in forearm resistance vessels of elderly women. AT₂-receptor blockade increases FVR, but does not prevent vasodilator responses to Ang II, suggesting that other vasodilator mechanisms may also be involved.

JRAAS 2002;3:36-39.

PAPERAcute and long-term effects of ACE inhibition on renal haemodynamics in glomerular and interstitial nephropathies
Ettore Guidi, Enrico E Minetti, Maria Grazia Cozzi

Background: Angiotensin-converting enzyme (ACE) inhibitors are the drugs of choice for the treatment of hypertension in patients with non-diabetic nephropathies. However, not every trial has reported better results with ACE inhibitors (ACE-I) than with other drugs. This study investigates whether the acute and chronic effects of ACE inhibition on renal and glomerular haemodynamics are similar in glomerular and interstitial nephropathies.
Methods: We studied 20 hypertensive patients, on their usual diet, with mild-to-moderate chronic renal failure secondary to non-diabetic nephropathy. After a three-week wash out period, we determined plasma clearances of para-amino-hippurate and inulin before, and after acute oral administration of either enalapril or ramipril. This same test was carried out after one and two years of treatment with the same drug.
Results: Acute ACE inhibition causes a decrease of renal perfusion, glomerular filtration and pressure with an increase of afferent resistances. Long-term ACE inhibition is associated only with a decrease in renal perfusion, with a non-significant tendency to higher filtration fraction and lower afferent resistances. All the renal haemodynamic modifications mentioned above are present only in patients with glomerular diseases.
Conclusions: Renal and glomerular haemodynamic responses are not similar after acute and chronic ACE inhibition. Only patients with glomerular diseases show acute or long-term responses to ACE inhibition.

JRAAS 2002;3:40-45.

PAPERStrain differences in angiotensin-converting enzyme and angiotensin II type I receptor expression. Possible implications for experimental chronic renal transplant failure
Annemieke Smit-van Oosten, Robert H Henning, Harry van Goor

Background: The Fisher to Lewis (F-L) model of renal transplantation (Rtx) is widely used. Rtx from F to L without immunosuppressive treatment results in 50% survival, whereas L to F results in survival rates similar to syngrafts. When treated with an angiotensin-converting enzyme (ACE) inhibitor or antihypertensive triple therapy, renal damage is markedly reduced in F-L allografts. Despite similar reductions in blood pressure, the ACE inhibitor (ACE-I) is more effective than antihypertensive triple therapy, suggesting that the inhibition of intrarenal ACE plays an additional role in the attenuation of renal damage.
Methods: In the present study, we investigated strain-related differences in intrarenal ACE activity between F and L rats and whether treatment with ACE-I in F-L allografted rats results in reduction of intrarenal ACE. Intrarenal ACE was measured by activity assays, immunohistochemistry and PCR.
Results: In control kidneys from healthy F rats (n=8), we found a four-fold higher ACE activity than in native L rats (n=8, p<0.01). This was confirmed by a three-fold difference in ACE mRNA expression (n=5 for both, p<0.01). Using immunohistochemistry, we found strong tubular ACE expression in the F rat, whereas the L rat had no tubular ACE at all.
In F-L allografts (n=9) we noted significant glomerulosclerosis and proteinuria after 34 weeks. Treatment with ACE-I in F-L (n=8) prevented the development of these changes. Although ACE mRNA and ACE protein expression were similar in treated and untreated allografts, intrarenal ACE activity was reduced by 50% in allografts with ACE-I.
Conclusion: In conclusion, intrarenal levels of ACE may play a role in the development of renal damage in experimental chronic renal transplant failure.

JRAAS 2002;3:46-53.

POPULAR
TOPICPAPERThe renin-angiotensin system does not contribute to the endothelial dysfunction and increased infarct size in rats exposed to second hand smoke
Bo-qing Zhu, Richard E Sievers, Amanda EM Browne, Robert T Hillman, Kamel Chair, Randall J Lee, Kanu Chatterjee, Stanton A Glantz, William W Parmley

Introduction: Both second hand smoke (SHS) and the renin-angiotensin system (RAS) contribute to endothelial dysfunction and increased infarct size in a rat ischaemia-reperfusion model. However, the potential interaction between SHS and the RAS is unknown.
Methods: Eighty-four rats were randomised into four groups: group C was a normal control; L was given 40 mg/kg/day of losartan in drinking water; SC and SL were exposed to SHS (smoking chamber) and given regular water or 40 mg/kg/day of losartan in drinking water, respectively. After six weeks of pre-treatment, rats were subjected to 17 minutes of left coronary artery occlusion and 2 hours of reperfusion with haemodynamic and ECG monitoring.
Results: Haemodynamics were not significantly different among the four groups. Losartan increased the threshold for ventricular fibrillation (p=0.0001) and reduced spontaneous ventricular arrhythmias (p=0.002) during ischaemia-reperfusion, while SHS did not (p=0.713, 0.110), and there was no interaction between losartan and SHS. The maximal endothelium-dependent vasorelaxation induced by a calcium ionophore (A23187) was increased by losartan (p=0.007). Myocardial infarct size was smaller in the losartan groups (p=0.032), larger in the SHS groups (p=0.0001), and there was no significant interaction.
Conclusion: In conclusion, losartan decreased infarct size and increased endothelium-dependent vasorelaxation. SHS exposure impaired endothelial function and increased infarct size. The effects of losartan and SHS were consistently independent of each other. These results suggest that the RAS does not contribute to the adverse effects of SHS.

JRAAS 2002;3:54-60.

POPULAR
TOPICEDITORIAL REVIEWRole of endothelin in cardiovascular disease
Alexei V Agapitov, William G Haynes

Endothelins are a family of peptides, which comprises endothelin-1 (ET-1), endothelin-2 (ET-2) and endothelin-3 (ET-3), each containing 21 amino-acids. ET-1 is a peptide secreted mostly by vascular endothelial cells, the predominant isoform expressed in vasculature and the most potent vasoconstrictor currently known. ET-1 also has inotropic, chemotactic and mitogenic properties. In addition, it influences salt and water homeostasis through its effects on the renin-angiotensin-aldosterone system (RAAS), vasopressin and atrial natriuretic peptide and stimulates the sympathetic nervous system.
The overall action of endothelin is to increase blood pressure and vascular tone. Therefore, endothelin antagonists may play an important role in the treatment of cardiac, vascular and renal diseases associated with regional or systemic vasoconstriction and cell proliferation, such as essential hypertension, pulmonary hypertension, chronic heart failure and chronic renal failure. Long-term anti-endothelin therapy may improve symptoms and favourably alter the progression of heart failure.
Endothelin appears to participate in induction and progression of sclerotic renal changes, leading to progression to end-stage renal disease. Anti-endothelin therapy might offer additional benefits in the prevention of progression of chronic renal failure in addition to the known benefits of RAAS inhibition.
Clinical trials have demonstrated potentially important benefits of endothelin antagonists for patients with essential hypertension, pulmonary hypertension and heart failure. Further studies are necessary to determine the role of anti-endothelin therapy in the treatment of cardiovascular diseases and determine the different roles of selective receptor antagonism vs. mixed ET_A/B-receptor antagonism in human diseases.

JRAAS 2002;3:1-15.