Proceedings of the Symposium ‘Angiotensin AT1 Receptors: From Molecular Physiology to Therapeutics’: EXPERIENCE WITH ANGIOTENSIN II ANTAGONISTS IN HYPERTENSIVE PATIENTS

Identification of five new bradykinin potentiating peptides (BPPs) from Bothrops jararaca crude venom by using electrospray ionization tandem mass spectrometry after a two-step liquid chromatography

Bradykinin potentiating peptides (BPPs) from Bothrops jararaca venom were described in the middle of 1960s and were the first natural inhibitors of the angiotensin-converting enzyme displaying strong anti-hypertensive effects in human subjects. The BPPs can be recognized by their typical pyroglutamyl proline-rich oligopeptide sequences presenting invariably a proline residue at the C-terminus. In the present study, we identified 18 BPPs, most of them already described for the B. jararaca venom. We isolated and sequenced new peptides ranging from 5 to 14 amino acid residues exhibiting similar amino acid sequence features. The applied methodology consisted of a strait two-step liquid chromatography, followed by mass spectrometry analysis. Besides the amino acid sequence homology, the corresponding synthetic peptides were able to potentiate bradykinin on the isolated guinea-pig ileum.

Angiotensin II AT1 receptor antagonism prevents detrimental renal actions of acute diuretic therapy in human heart failure

Although effective in relieving symptoms of edema in congestive heart failure (CHF), diuretic-induced natriuresis may be associated with reductions in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), which subsequently may reduce the duration of natriuresis. Moreover, recent studies have reported that the preservation of GFR is an important predictor of survival in human CHF. We hypothesized that the acute detrimental renal hemodynamic and tubular responses to furosemide in symptomatic human CHF will be attenuated by AT(1) receptor blockade with losartan. We defined the renal hemodynamic and tubular actions and aldosterone responses to furosemide (40 mg, orally) in the presence of acute AT(1) receptor antagonism (losartan, MSD, 50 mg orally) vs. placebo in 10 subjects with CHF (New York Heart Association II-III) in a double-blind, placebo-controlled crossover study. Furosemide with placebo increased sodium excretion and reduced ERPF and GFR (P < 0.05 vs. baseline). After 4 h, sodium excretion compared with baseline was decreased (P < 0.05). In contrast, furosemide with losartan resulted in a greater increase in sodium excretion but without reductions in ERPF and GFR (P < 0.05 vs. placebo). After 4 h, sodium excretion was greater compared with the placebo group. Importantly, plasma aldosterone tended to increase in the placebo group, whereas it was decreased (P < 0.05 vs. baseline) only in the losartan group. These studies underscore the pathophysiological role of the AT(1) receptor in mediating detrimental renal and adrenal properties of diuretics in human CHF. AT(1) receptor antagonism preserves GFR and renal blood flow and enhances sodium excretion during acute diuretic therapy in addition to inhibiting aldosterone secretion. These findings support the use of AT(1) receptor blockade for human CHF requiring acute diuretics to improve renal hemodynamic and tubular function and to suppress aldosterone.

The pharmacologic treatment of uncomplicated arterial hypertension in patients with airway dysfunction

Because many antihypertensive drugs can affect airway function, the treatment of hypertension in patients with airway dysfunction is complex. For example, the worsening or precipitation of asthma by beta-adrenoceptor antagonists is well-recognized, but beta(1)-adrenoceptor blockers that exert mild beta(2)-agonist effects, and those that modulate the endogenous production of nitric oxide, affect airway function to a lesser extent. Therapy with selective alpha(1)-blockers is not contraindicated in cases of chronic airway obstruction. Conversely, alpha(2)-agonists must not be given to asthmatic subjects because they can adversely affect the bronchi. Calcium channel blockers do not exert severe side effects on the airways. Angiotensin-converting enzyme inhibitors may cause cough and exacerbate or even induce asthma; however, angiotensin II type I (AT(1)) antagonists do not cause cough. 5-Hydroxytryptamine modifiers such as urapidil are a treatment option for patients with chronic airway obstruction. In patients with airway dysfunction, we suggest treatment with thiazide diuretics as the initial drug choice, and calcium channel blockers if the response is poor. In the case of no response, calcium channel blockers alone must be used. However, there is no strict rule because individual patients may respond differently to individual drugs and drug combinations. Consequently, it is important to adopt a flexible approach. For patients who are unresponsive to the aforementioned drugs, AT(1) receptor antagonists, newer beta(1)-adrenoceptor-blocking agents with ancillary properties (eg, celiprolol or nebivolol), and/or vasodilators can be considered.

Practical considerations of the pharmacology of angiotensin receptor blockers

A review of the drug class of angiotensin receptor blockers (ARBs) as well as the ARBs currently available by prescription in the United States is presented. The importance of angiotensin II production by non-angiotensin-converting enzyme (non-ACE) pathways, particularly human chymase, is discussed. Emphasis is placed on the mechanism of action of ARBs and the different binding kinetics of these agents. Although all ARBs, as a group, block the AT1 receptor, they may differ in the pharmacological characteristics of their binding and be classified as either surmountable or insurmountable antagonists. Mechanisms of surmountable and insurmountable antagonism as well as possible benefits of these blocking characteristics are discussed in relation to the various ARBs. The cardiovascular effects of activation of the two main subtypes of angiotensin receptors (AT1 and AT2) are presented. In addition to their treatment of hypertension, ACE inhibitors are recognized as being effective in the management of heart failure, left ventricular hypertrophy, recurrent myocardial infarctions, and renal disease. ARBs are currently indicated only for the treatment of hypertension; however, in vitro and in vivo pharmacological studies as well as preliminary clinical data suggest that ARBs, like ACE inhibitors, may also provide effective protection against end-organ damage in these conditions.

Alpha-adrenergic blocking drugs in the management of benign prostatic hyperplasia: interactions with antihypertensive therapy

Management of benign prostatic hyperplasia (BPH) is often complicated by concomitant hypertension, a life-threatening condition that must be managed optimally. Many of the alpha blockers used to treat BPH also decrease blood pressure, and terazosin and doxazosin have been shown to have significant cardiovascular side effects, such as asthenia/fatigue, postural hypotension, and dizziness when used to treat BPH patients. Furthermore, these drugs are not first-line therapies for hypertension, and the majority of hypertensive BPH patients will be receiving other antihypertensive agents. Therefore, it is possible that the introduction of these drugs will affect blood pressure control, at least temporarily, with possible adverse effects. In contrast, the selective alpha1A blocker tamsulosin does not appear to have significant cardiovascular side effects and produces minimal blood pressure reductions. Therefore, urologists can choose either to use alpha blockers to treat both hypertension and BPH or to treat BPH using alpha blockers that do not interact with antihypertensive therapy. This review focuses on the alpha blockers currently being used to treat BPH, their effects on the cardiovascular system, and their interaction with antihypertensive drugs.