Effect of aspirin on vasodilation to bradykinin and substance P in patients with heart failure treated with ACE inhibitor

Effects of bradykinin on venous capacitance in health and treated chronic heart failure

In the present study, we investigated the effects of basal and intra-arterial infusion of bradykinin on unstressed forearm vascular volume (a measure of venous tone) and blood flow in healthy volunteers (n=20) and in chronic heart failure patients treated with ACEIs [ACE (angiotensin-converting enzyme) inhibitors] (n=16) and ARBs (angiotensin receptor blockers) (n=14). We used radionuclide plethysmography to examine the effects of bradykinin and of the bradykinin antagonists B9340 [B1 (type 1)/B2 (type 2) receptor antagonist] and HOE140 (B2 antagonist). Bradykinin infusion increased unstressed forearm vascular volume in a similar dose-dependent manner in healthy volunteers and ARB-treated CHF patients (healthy volunteers maximum 12.3±2.1%, P<0.001 compared with baseline; ARB-treated CHF patients maximum 9.3±3.3%, P<0.05 compared with baseline; P=not significant for difference between groups), but the increase in unstressed volume in ACEI-treated CHF patients was higher (maximum 28.8±7.8%, P<0.001 compared with baseline; P<0.05 for the difference between groups). In contrast, while the increase in blood flow in healthy volunteers (maximum 362±9%, P<0.001) and in ACEI-treated CHF patients (maximum 376±12%, P<0.001) was similar (P=not significant for the difference between groups), the increase in ARB-treated CHF patients was less (maximum 335±7%, P<0.001; P<0.05 for the difference between groups). Infusion of each receptor antagonist alone similarly reduced basal unstressed volume and blood flow in ACEI-treated CHF patients, but not in healthy volunteers or ARB-treated CHF patients. In conclusion, bradykinin does not contribute to basal venous tone in health, but in ACEI-treated chronic heart failure it does. In ARB-treated heart failure, venous responses to bradykinin are preserved but arterial responses are reduced compared with healthy controls. Bradykinin-mediated vascular responses in both health and heart failure are mediated by the B2, rather than the B1, receptor.

Pharmacological modulation of cGMP levels by phosphodiesterase 5 inhibitors as a therapeutic strategy for treatment of respiratory pathology in cystic fibrosis

The CFTR gene encodes a chloride channel with pleiotropic effects on cell physiology and metabolism. Here, we show that increasing cGMP levels to inhibit epithelial Na(+) channel in cystic fibrosis (CF) respiratory epithelial cells corrects several aspects of the downstream pathology in CF. Cell culture models, using a range of CF cell lines and primary cells, showed that complementary pharmacological approaches to increasing intracellular cGMP, by elevating guanyl cyclase activity though reduced nitric oxide, addition of cell-permeable cGMP analogs, or inhibition of phosphodiesterase 5 corrected multiple aspects of the CF pathological cascade. These included correction of defective protein glycosylation, bacterial adherence, and proinflammatory responses. Furthermore, pharmacological inhibition of phosphodiesterase 5 in tissues ex vivo or in animal models improved transepithelial currents across nasal mucosae from transgenic F508del Cftr(tm1Eur) mice and reduced neutrophil infiltration on bacterial aerosol challenge in Pseudomonas aeruginosa-susceptible DBA/2 mice. Our findings define phosphodiesterase 5 as a specific target for correcting a number of previously disconnected defects in the CF respiratory tract, now linked through this study. Our study suggests that phosphodiesterase 5 inhibition provides an opportunity for simultaneous and concerted correction of seemingly disparate complications in CF.

Modulating atherosclerosis through inhibition or blockade of angiotensin

Angiotensin-convertng enzyme (ACE) inhibitors are well recognized for their benefits in treating hypertension and congestive heart failure and preventing postmyocardial infarction heart failure or left ventricular (LV) dysfunction. Recently, blockade of the angiotensin II type 1 (AT1) receptor was shown to reduce cardiovascular events in hypertensive subjects with LV hypertrophy. Several lines of evidence are now converging to show that ACE inhibitors may affect the atherosclerotic process itself. Emerging clinical data indicate that angiotensin-receptor blockers (ARBs) may possibly modulate atherosclerosis as well. The antiatherogenic properties of ACE inhibitors and ARBs may derive from inhibition or blockade of angiotensin II, now recognized as an agent that increases oxidative stress.Angiotensin-converting enzyme inhibition and angiotensin-receptor blockade also increase endothelial nitric oxide formation, which improves endothelial function. In contrast to the effects of ARBs, the vascular effects of ACE inhibitors may, in part, be mediated by an increase in bradykinin. This article reviews some of the biologic mechanisms whereby ACE inhibitors and ARBs may modulate atherosclerosis.

Comparative effects of aspirin with ACE inhibitor or angiotensin receptor blocker on myocardial infarction and vascular function

OBJECTIVES

We previously showed that an angiotensin-converting enzyme inhibitor (captopril) or an angiotensin receptor blocker (losartan) reduced infarct size and improved endothelial function in a rat model of ischaemia-reperfusion. The present study was undertaken to see if aspirin (ASA) antagonised the beneficial effects of captopril or losartan.

METHODS

One hundred and fourteen Sprague-Dawley rats were randomised into six groups; Control, ASA, captopril, losartan, ASA+captopril, and ASA+losartan. ASA, captopril or losartan were given at a concentration of 40 mg/kg/day in drinking water. After six weeks of pre-treatment, the rats were subjected to 17 minutes of left anterior descending coronary artery occlusion and 120 minutes of reperfusion, with haemodynamic and ECG monitoring. During the reperfusion period, the effective refractory period (ERP), ventricular fibrillation threshold (VFT) and bleeding time (BT) were measured. In fresh aortic rings precontracted with phenylephrine, endothelium-dependent and -independent relaxations were assessed using acetylcholine and nitroglycerin.

RESULTS

Haemodynamic changes were not different between the groups. Serum ASA concentrations were 0.5, 1.1 and 0.6 mg/dl in the ASA, ASA+captopril and ASA+losartan groups, respectively, and BT was prolonged (p<0.01). ASA alone reduced endothelium-dependent relaxation (-29+8 vs. -69+11%, p<0.01), but did not change endothelium-independent relaxation. ASA did not affect endothelial relaxation induced by acetylcholine in the presence of either captopril or losartan. Angiotensin I and ERP were elevated by captopril and losartan. Angiotensin II and VFT were elevated by losartan. ASA with captopril, captopril and losartan equally reduced infarct size, compared with control (39+3, 39+4, and 39+5 vs. 53+3%, all p<0.05).

CONCLUSIONS

Captopril and losartan had similar cardiovascular protective effects in a rat model of ischaemia-reperfusion. Aspirin did not attenuate the cardiovascular protective effects of captopril or losartan.