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Current research on angiotensin II AT1-receptor antagonists (AIIRAs) and selected studies presented at the recent symposium held in Amsterdam, The Netherlands, on 6 June 1998, titled 'Angiotensin II Receptor Antagonists are NOT all the Same' are reviewed. AIIRAs offer a number of potential advantages over alternative antihypertensive agents acting via the renin-angiotensin-aldosterone system. They combine blood pressure-lowering effects at least equivalent to those of angiotensin-converting enzyme (ACE) inhibitors, coupled with placebo-like tolerability. Candesartan cilexetil is a novel AIIRA that has demonstrated clinical efficacy superior to losartan, has a sustained duration of action over 24 hours (trough:peak ratio close to 100%) and is well tolerated in patients with essential hypertension. Candesartan cilexetil has a rapid onset of action (approximately 80% of total blood pressure reduction within the first 2 weeks) and dose-dependent effects on blood pressure, is comparable in efficacy to a number of classes of antihypertensives, and is effective in combination therapy (eg, with hydrochlorothiazide and amlodipine). This favourable profile may be due in part to the highly selective, tight binding to and slow dissociation of candesartan from the AT1 receptor. Preliminary studies suggest that candesartan cilexetil also protects end organs (kidney, heart, vasculature, and brain) beyond blood pressure control.
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PMID:Key features of candesartan cilexetil and a comparison with other angiotensin II receptor antagonists. 1007 15

Components of the renin-angiotensin system play an important role in the normal regulation of blood pressure. We carried out a comprehensive genetic linkage study of the genes involved in the renin-angiotensin cascade in Finnish hypertensive twins and their affected siblings. We found no evidence for linkage between essential hypertension and the genes coding for renin, angiotensinogen, angiotensin-converting enzyme, or kallikrein 1 in the 329 hypertensive individuals of 142 families studied. In contrast, two intragenic markers for the type 1 angiotensin II receptor (AT1) showed some evidence for linkage in the total sample. A closer examination of this gene locus was carried out using subgroups of nonobese sibpairs with early onset of hypertension and uniform geographical origin. These stratifications yielded suggestive evidence for linkage of hypertension to the genetic area containing the AT1 gene, with a maximal multipoint logarithm of the odds (LOD) score of 2.9. A genetic association study carried out in an independent series of 50 hypertensive cases and 122 normotensive controls showed an increase in the frequency of the A1166-->C allele of the AT1 gene in the hypertensive individuals. In a novel variant of model-free multipoint linkage analysis allowing linkage disequilibrium in the calculations, an LOD score of 5.13 was obtained. Sequence analyses of the entire coding region and 848 bp of promoter region in the DNA sample on 8 index samples did not reveal previously unpublished sequence variations. The data provide evidence that a common genetic variant of the AT1 gene locus influences the risk of essential hypertension in the Finnish population.
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PMID:Evidence for involvement of the type 1 angiotensin II receptor locus in essential hypertension. 1008 97

Immune mechanisms and the renin-angiotensin system are implicated in preeclampsia. We investigated 25 preeclamptic patients and compared them with 12 normotensive pregnant women and 10 pregnant patients with essential hypertension. Antibodies were detected by the chronotropic responses to AT1 receptor-mediated stimulation of cultured neonatal rat cardiomyocytes coupled with receptor-specific antagonists. Immunoglobulin from all preeclamptic patients stimulated the AT1 receptor, whereas immunoglobulin from controls had no effect. The increased autoimmune activity decreased after delivery. Affinity-column purification and anti-human IgG and IgM antibody exposure implicated an IgG antibody directed at the AT1 receptor. Peptides corresponding to sites on the AT1 receptor's second extracellular loop abolished the stimulatory effect. Western blotting with purified patient IgG and a commercially obtained AT1 receptor antibody produced bands of identical molecular weight. Furthermore, confocal microscopy of vascular smooth muscle cells showed colocalization of purified patient IgG and AT1 receptor antibody. The protein kinase C (PKC) inhibitor calphostin C prevented the stimulatory effect. Our results suggest that preeclamptic patients develop stimulatory autoantibodies against the second extracellular AT1 receptor loop. The effect appears to be PKC-mediated. These novel autoantibodies may participate in the angiotensin II-induced vascular lesions in these patients.
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PMID:Patients with preeclampsia develop agonistic autoantibodies against the angiotensin AT1 receptor. 1019 66

The angiotensin II (AII) receptor antagonist eprosartan is a highly selective, nonpeptide drug specific for the AT1 receptor subtype that completely inhibits pressor, aldosterone secretory, and renal vasoconstrictive effects produced by AII infusions in healthy humans. It increases effective renal plasma flow in both salt-replete and salt-restricted healthy men, and maintains glomerular filtration rates in patients with essential hypertension and those with renal insufficiency after either single or multiple doses. In healthy salt-restricted men, the drug suppresses and stimulates aldosterone and renin, respectively, in the initial few hours after administration. This feedback inhibition for renin release and suppression of aldosterone is reduced with normal sodium intake. Eprosartan is natriuretic in salt-restricted subjects and does not induce sodium retention even when it reduces blood pressure. These properties, in addition to antagonism of AII effect at the AT1 receptor, no doubt contribute to the agent's antihypertensive effect in patients with essential hypertension. Pharmacodynamic studies predict that doses of up to 400 mg are safe. Additional preliminary studies suggest that doses as high as 1200 mg are safe and well tolerated, while producing meaningful hemodynamic and neurohumoral effects in patients with essential hypertension.
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PMID:The renal profile of eprosartan. 1021 27

Insulin resistance and hypertension commonly occur together. Pharmacological inhibition of the renin-angiotensin system has been found to reduce not only hypertension, but also insulin resistance. This raises the possibility that the renin-angiotensin system may interact with insulin signalling. We have investigated the relationship between insulin and angiotensin II (AII) intracellular signalling in vivo using an intact rat heart model, and in vitro using rat aorta smooth muscle cells (RASMC). Results generated in the in vivo studies indicate that, like insulin, AII stimulates tyrosine phosphorylation of the insulin receptor substrates IRS-1 and IRS-2. This leads to binding of IRS-1 and IRS-2 to PI3-kinase. However, in contrast to the effect of insulin. IRS-1- and IRS-2-associated PI3-kinase activity is inhibited by AII in a dose-dependent manner. Moreover, AII inhibits insulin-stimulated IRS-1/IRS-2-associated PI3-kinase activity. The in vivo effects of AII are mediated via the AT1 receptor. The results of the in vitro studies indicate that AII inhibits insulin-stimulated, IRS-1-associated PI3-kinase activity by interfering with the docking of IRS-1 with the p85 regulatory subunit of PI3-kinase. It appears that AII achieves this effect by stimulating serine phosphorylation of the insulin receptor beta-subunit IRS-1, and the p85 regulatory subunit of PI3-kinase. These actions result in the inhibition of normal interactions between the insulin signalling pathway components. Thus, we believe that AII negatively modulates insulin signalling by stimulating multiple serine phosphorylation events in the early components of the insulin signalling cascade. Overactivity of the renin-angiotensin system is likely to impair insulin signalling and contribute to insulin resistance observed in essential hypertension.
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PMID:Crosstalk between insulin and angiotensin II signalling systems. 1032 50

The angiotensin II (A II) type 1 receptor (AT1) antagonists represent a new pharmacologic class of drugs. These drugs antagonize A II induced biologic actions. Initial clinical trials suggest that these drugs are effective in the treatment of essential hypertension and hypertensive patients with renal disease. Losartan becomes the first potent, orally active and longacting nonpeptide A II receptor antagonist to be used in humans. Antihypertensive efficacy appears to be dependent on an activation of renin-angiotensin system, since bilateral nephrectomy and/or volume expansion abolishes the blood pressure lowering effect. Blood pressure is lowered without a significant change in heart rate or cardiac output. In hypertensive patient with renal disease, losartan has been reported to have no clinically important effect on glomerular filtration rate. To date, no specific AT1 antagonists' side effect has been reported. The potential widespread use of this new class of antihypertensive drugs will depend on whether AT1 receptor antagonists can be differentiated clinically from ACE inhibitors, and if such differentiation has clinically significant benefits.
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PMID:[Losartan: angiotensin II type 1 receptor antagonist]. 1033 25

Valsartan/hydrochlorothiazide (HCTZ) combines an angiotensin II AT1 receptor blocker with a thiazide diuretic to produce additive blood pressure reductions without major effects on heart rate. HCTZ did not significantly alter valsartan pharmacokinetics; during combination therapy, HCTZ pharmacokinetics differed from those seen with HCTZ monotherapy. In clinical trials in patients with essential hypertension, adding HCTZ 12.5 or 25 mg/day to valsartan 80 mg/day resulted in a greater blood pressure reduction than increasing the valsartan dosage from 80 to 160 mg/day. The valsartan/HCTZ combination was generally more effective than either drug given alone. Efficacy of the combination was maintained during up to 3 years of treatment. Valsartan/HCTZ was well tolerated in both short and long term trials. The most common adverse events were dizziness, headache and fatigue. The overall incidence of adverse events with the combination was similar to that with placebo. HCTZ-induced hypokalaemia was less common during combination therapy.
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PMID:Valsartan/hydrochlorothiazide. 1035

Nonpeptide angiotensin II type 1-receptor antagonists, AT1 receptor antagonists, are newly developed and useful drugs for essential hypertension. In Japan, the efficacy and safty of losartan and candesartan cilexetil in patients with essential hypertension have been evaluated by the double-blind, parallel group-comparison study using enelaprol maleate as control drug. Both trials revealed that these drugs showed a hypotensive effect comparable to that of enalapril with a high safety since the adverse drug reaction of cough was recognized in very few patients. Since the blood pressure normalizes only in the patient of about 50%, it is often required to add low-dose hydrochlorothiazide or calcium antagonist. Combination therapies further decreased blood pressure without any increases in side effects of the drugs. AT1 receptor antagonists in both mono-therapy and combination therapy with diuretics/Ca antagonists are very useful and safe in the hypertension treatment.
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PMID:[The usefulness of a new class antihypertensive drug, angiotensin II receptor antagonist, for essential hypertension]. 1036 48

A lot of evidence points to the important role of the renin-angiotensin system in the physiopathology of hypertension and the progression of chronic renal failure. In this review, the authors report the data concerning the protective effects of antagonists of angiotensin II AT1 receptors (AT1ra). The AT1 ra have been shown to have beneficial effects in most experimental models of nephropathy in which they have been tested (renal ischaemia, essential or induced hypertension, glomerulonephritis, 5/6 nephrectomy, renal transplantation, induced diabetes, toxic and radiotherapy-induced nephropathy). Clinical trials confirm these beneficial effects. In healthy subjects and hypertensive patients, the AT1 ra have identical effects to those of angiotensin converting enzyme (ACE) inhibitors on renal haemodynamics. In hypertensives, Candesartan and Irbesartan increase renal blood flow and the glomerular filtration rate and decrease the filtration fraction. Two studies have also shown that Candesartan and Irbesartan reduce proteinuria in diabetic patients. Similar results have been reported in essential hypertension with renal failure. These data suggest that AT1 ra have beneficial effects on the progression of experimental kidney disease and on proteinuria in the clinical setting. Of the pharmacological agents available for use in this class, it is essential to propose molecules whose efficacy in antagonising the effects of angiotensin II lasts throughout the 24 hour period. Clinical trials are under way to evaluate the effects of AT1 ra on renal function in man over a long period.
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PMID:[Are the antagonists of angiotensin II AT1 receptors protectors of the kidney?]. 1044 11

Recent developments in molecular biological techniques allowed us to examine the genetic risk factors responsible for essential hypertension. The candidate gene approach revealed that several gene polymorphisms increase the relative risk for hypertension. Most genetic studies, however, examined only young subjects but not elderly ones. To examine the importance of gene polymorphisms in elderly hypertension, we carried out a case-control study and compared the odds ratio for hypertension between young (< 60) and elderly (> or = 60) subjects. The participants of this study were recruited from the outpatients of Osaka University Medical School with informed consent. We examined the following polymorphisms as candidates: the angiotensinogen (AGT/M235T), angiotensin converting enzyme (ACE I/D), angiotensin II type 1 (AT1/A1166C) and type 2 (AT2/C3123A) receptors, alpha-adducin (adducin/Gly460Trp), methylenetetrahydrofolate reductase (MTHHR/C677T), and apolipoprotein (apoE/epsilon 4, apoE/T-491A). In young subjects, the AGT/T235 allele significantly increased the odds ratio for hypertension but not in elderly subjects. In young males, the AT2/A3123 allele was also associated with hypertension but not in females or in elderly subjects. Other associations between polymorphism and hypertension did not reach a significant level. To sum up, it was revealed that some polymorphisms increase the susceptibility for hypertension but others do not, which suggests that there is heterogeneity in the genetic involvement of polymorphism due to aging.
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PMID:[Genetic analysis of candidate gene polymorphisms in elderly hypertension]. 1055 62


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