ACE-inhibitor-induced enhancement of spontaneous and IgE-mediated histamine release from mast cells and basophilic leukocytes and the modulatory effect of capsaicin sensitive nerves

The immunomodulatory effects of antihypertensive therapy: A review

Hypertension remains the leading preventable risk factor for stroke and coronary artery disease, significantly contributing to all-cause global mortality and predisposing patients to renal and heart failure, as well as peripheral vascular disease. Due to the widespread usage of antihypertensive drugs, global mean blood pressure has remained unchanged or even slightly decreased over the past four decades. However, considering the broad spectrum of mechanisms involved in the action of antihypertensive drugs and the prevalence of their target receptors on immune cells, possible immunomodulatory effects which may exert beneficial effects of lowering blood pressure but also potentially alter immune function should be considered. In this review, we attempt to assess the consequences to immune system function of administering the five most commonly prescribed groups of antihypertensive drugs and to explain the mechanisms behind those interactions. Finally, we show potential gaps in our understanding of the effects of antihypertensive drugs on patient health. With regard to the widespread use of these drugs in the adult population worldwide, the discussed results may be of vital importance to evidence-based decision-making in daily clinical practice.

Angiotensin-converting enzyme inhibitors can potentiate ozone-induced airway hyperresponsiveness

We investigated the effects of single and chronic oral administration of angiotensin-converting enzyme inhibitors on ozone-induced airway hyperresponsiveness in guinea pigs. Ozone exposure (3 ppm for 2 h) significantly increased airway responsiveness in vehicle-treated animals and in animals with either single or chronic administration (8 days) of drugs. Single administration of imidapril, enalapril and captopril significantly potentiated ozone-induced airway hyperresponsiveness at a dose of 100, 50 and 50 mg/kg, respectively, although these doses did not influence airway responsiveness in normal guinea pigs, i.e., the magnitude of potentiation was captopril > enalapril > imidapril. In the study of chronic administration of the drugs, imidapril (10-100 mg/kg per day) had no influence on airway responsiveness in both normal and ozone-treated animals. In contrast, captopril and enalapril (10-100 mg/kg per day) dose-dependently potentiated ozone-induced airway hyperresponsiveness, with no influence on airway responsiveness in normal animals. That is, the magnitude was enalapril > captopril. These results indicate that angiotensin-converting enzyme inhibitors potentiate airway responsiveness in ozone-treated guinea pigs but not in normal guinea pigs and that imidapril is less potent than enalapril and captopril in potentiating ozone-induced airway hyperresponsiveness in guinea pigs.

Pulmonary C-fiber activation before and after peptidase inhibition in rats

Inhibition of peptidases within the lungs not only potentiates the effects of neuropeptides released from C-fibers but also the effects of bradykinin and capsaicin both of which stimulate C-fibers. To determine if peptidase inhibition potentiates C-fiber activation, we challenged pulmonary C-fibers in rats with capsaicin or bradykinin before and after inhibition of neutral endopeptidase (NEP) or angiotensin converting enzyme (ACE). Inhibition of NEP by phosphoramidon (10 mg/kg, i.v.) potentiated the effect of capsaicin (0.5-1 micrograms, i.v.) on C-fiber activity but did not change the response to bradykinin (1-2 micrograms, i.v.). Inhibition of ACE by captopril (5 mg/kg, i.v.) potentiated C-fiber activation by either bradykinin or capsaicin. Aerosol administration of either phosphoramidon (1 x 10(-5) M, 2 min) or captopril (4.6 x 10(-3) M, 2 min) potentiated C-fiber activation by capsaicin aerosol (1.6 x 10(-4) M, 1 min) but not by bradykinin aerosol (9.4 x 10(-5) M, 1 min). Therefore, inhibition of NEP or ACE may potentiate airway obstructive mechanisms initiated by C-fiber stimulation.

The effect of compound 48/80 on contractions induced by toluene diisocyanate in isolated guinea-pig bronchus

We have investigated the ability of compound 48/80 and of histamine H1 and H2 receptor antagonists to inhibit toluene diisocyanate-induced contractions in isolated guinea-pig bronchi. Compound 48/80 (100 micrograms/ml) significantly inhibited toluene diisocyanate-induced contractions. By contrast, the two histamine H1 and H2 receptor antagonists, chlorpheniramine (10 microM) and cimetidine, (10 microM) did not affect toluene diisocyanate-induced contractions, but significantly inhibited contractions induced by exogenously applied histamine (100 microM) and by 48/80. We investigated which mechanisms 48/80 used to inhibit toluene diisocyanate-induced contractions, paying particular attention to the possible involvement of capsaicin-sensitive primary afferents. In vitro capsaicin desensitization (10 microM for 30 min followed by washing) significantly reduced compound 48/80-induced contractions. A capsaicin-resistant component of contraction was also evident. Ruthenium red (3 microM), an inorganic dye which acts as a selective functional antagonist of capsaicin, did not affect 48/80-induced contraction. MEN 10,207 (Tyr5,D-Trp6,8,9,Arg10)-neurokinin A (4-10) (3 microM) a selective antagonist of NK2-tachykinin receptors significantly reduced 48/80-induced contractions. These results show that compound 48/80 inhibits toluene diisocyanate-induced contractions in isolated guinea-pig bronchi. It is likely that two mechanisms are involved in the inhibition: (1) the release of mediators other than histamine by mast cells, (2) an effect of 48/80 on sensory nerves.

Could the pharmacological differences observed between angiotensin II antagonists and inhibitors of angiotensin converting enzyme be clinically beneficial?

Over the past several years, angiotensin I converting enzyme (ACE) inhibitors, compounds that block the formation of angiotensin II (ANG II), have become widely used in the treatment of cardiovascular disease. Recently, a new class of orally active, non-peptide inhibitors of the renin-angiotensin system, the ANG II receptor antagonists have also become available. Since both classes of compounds block the renin-angiotensin system, although at different sites, it remains to be determined whether blockade of ANG II receptors will have any specific advantage over inhibition of ACE. The following review assesses the actions of ANG II antagonists and suggests ways in which blockade of ANG II receptors may differ both pharmacologically and clinically from inhibition of ACE.

Anaphylactoid reactions in hemodialysis patients treated with the AN69 dialyzer

During an 11 week period (May to July, 1990), we observed six anaphylactoid reactions (AR) in six different hemodialysis patients occurring at the onset of treatment with a new AN69 hollow-fiber dialyzer. Four patients required cardiopulmonary resuscitation and one of these expired. Four patients were also receiving an angiotensin converting enzyme (ACE) inhibitor while the other two were not on medication known to affect the renin-angiotensin system. Only patients treated with AN69 dialyzers were affected. A review of the literature indicated that out of 1087 patients reported, 72 patients were on the combination of an AN69 dialyzer and ACE inhibitor therapy and 41 (57%) demonstrated AR. Only two patients (0.4%; both from our series) treated with an AN69 dialyzer without ACE inhibitor therapy developed AR. AR did not occur in patients treated with a variety of other dialyzers during this 11 week period, with or without ACE inhibition. Possible causes for AR are discussed and include: (1.) blood-AN69 membrane interaction leading to the production of bradykinin and other vasodilators, the breakdown of which may be delayed by the presence of ACE inhibitors; (2.) hypersensitivity to ethylene oxide; (3.) passage of bacterial products from dialysate to blood; (4.) changes in membrane manufacturing specifications. Recommendations are proposed for the prevention and treatment of AR.

Enalaprilat, but not cilazaprilat, increases inflammatory skin reactions in guinea-pigs

The inflammatory effects of enalaprilat and cilazaprilat were tested in an experimental model of ovalbumin-sensitised guinea-pigs. Enalaprilat, but not cilazaprilat, enhanced the ovalbumin-induced inflammatory skin responses. The effect of enalaprilat was dose-dependent. Enalaprilat significantly increased the skin content of substance P and histamine. Cilazaprilat did not alter the level of these inflammatory mediators. Enalaprilat, applied locally, but not cilazaprilat, enhanced the inflammatory reactions caused by intradermal injections of allergen and substance P. Both angiotensin converting enzyme (ACE) inhibitors enhanced the inflammatory skin response evoked by bradykinin. Our study strongly indicates that enalaprilat has pro-inflammatory properties, whereas the new long-acting ACE inhibitor cilazaprilat does not. This might give a better safety profile of cilazaprilat.