Participation of angiotensin II and bradykinin in contractile function in dog stunned myocardium

The effect of telmisartan on the ventricular systolic function in dogs with experimental supraventricular tachyarrhythmia

Maintaining a good ventricular systolic function is important in the long-term therapy of dogs with supraventricular tachyarrhythmia (SVTA). The objective of this study was to evaluate the inhibitory effect of telmisartan on myocardial injury and the resulting ventricular systolic dysfunction in a canine model of SVTA. A total of 14 dogs were randomly assigned to a Telmisartan (oral telmisartan, 1.0 mg/kg daily, n=7) or a Control (no drug administration, n=7) group; the duration of rapid atrial pacing (RAP) was 3 weeks for both groups. The cardiac troponin I (cTnI) concentration in the Control group was significantly increased after 3 weeks compared to that before RAP initiation (baseline), but no significant difference was observed in the Telmisartan group. Moreover, the cTnI concentration at 3 weeks was significantly lower in the Telmisartan group than in the Control group. The left ventricular fractional shortening was significantly decreased at 3 weeks compared to that at baseline in both groups. However, fractional shortening at 3 weeks was significantly higher in the Telmisartan group than in the Control group. The cardiac output values in the Control group were significantly decreased at 3 weeks compared with those at baseline, but no significant difference was observed in the Telmisartan group. This study demonstrates that telmisartan inhibits the reduction in ventricular systolic function and prevents myocardial injury in a canine model of SVTA. Therefore, telmisartan is suggested as a novel treatment for canine SVTA.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

Attentuation of cardiac stunning by losartan in a cellular model of ischemia and reperfusion is accompanied by increased sarcoplasmic reticulum Ca2+ stores and prevention of cytosolic Ca2+ elevation

This study investigates whether protective effects of an angiotensin II type 1 receptor antagonist (losartan) in ischemia and reperfusion are mediated by actions on Ca(2+) cycling. Effects of exposure to losartan (10 microM) in ischemia were evaluated in isolated guinea pig ventricular myocytes exposed to simulated ischemia and reperfusion at 37 degrees C. Field-stimulated myocytes were exposed to 30 min of simulated ischemia (hypoxia, acidosis, lactate, hyperkalemia, and glucose-free) and reperfusion with Tyrode's solution for 40 min. Cell shortening was measured with a video edge detector, and Ca(2+) concentration was measured with fura-2. Field-stimulated myocytes exhibited stunning in reperfusion, which was abolished in cells exposed to losartan. In microelectrode studies, losartan did not alter the responses of resting potentials or action potentials to ischemia and reperfusion. In the absence of losartan, diastolic Ca(2+) increased in ischemia, and Ca(2+) transients exhibited a rebound overshoot in early reperfusion. Losartan did not affect amplitudes of Ca(2+) transients in ischemia but prevented elevations in diastolic Ca(2+) in ischemia. Furthermore, losartan prevented the overshoot of Ca(2+) transients in early reperfusion and increased the magnitude of Ca(2+) transients in late reperfusion. Sarcoplasmic reticulum (SR) Ca(2+) stores, determined as Ca(2+) released by rapid application of 10 mM caffeine, were not altered in ischemia and reperfusion. However, losartan increased SR Ca(2+) stores in late reperfusion, even in cells that were not exposed to simulated ischemia. We conclude that losartan abolishes stunning in reperfusion by preserving normal diastolic Ca(2+) in ischemia and by increasing Ca(2+) transients through elevation of releasable SR Ca(2+).

Telmisartan: a review of its use in hypertension

Telmisartan is an angiotensin II receptor antagonist that is highly selective for type 1 angiotensin II receptors. It was significantly more effective than placebo in large (n >100), double-blind, randomised, multicentre clinical trials in patients with mild to moderate hypertension. Telmisartan 20 to 160 mg once daily produced mean reductions in supine trough systolic blood pressure and diastolic blood pressure of up to 15.5 and 10.5 mm Hg, respectively. Maximum blood pressure reduction occurred with a dosage of 40 to 80 mg/day. Telmisartan 40 to 120 mg/day was as effective as amlodipine 5 to 10 mg/day or atenolol 50 to 100 mg/day in dose-titration studies. Telmisartan 20 to 160 mg/day was generally similar in efficacy to enalapril 5 to 20 mg/day or lisinopril 10 to 40 mg/day in both titration-to-response and other studies. Hydrochlorothiazide was coadministered in most of the titration-to-response studies if patients remained hypertensive. Telmisartan 80 mg/day was more effective than submaximal dosages of losartan (50 mg/day) or valsartan (80 mg/day) and was as effective as a fixed-dose combination of losartan 50 mg plus hydrochlorothiazide 12.5 mg over the last 6 hours of the dosage interval and the whole 24-hour postdose interval. In patients with severe hypertension, telmisartan 80 to 160 mg/day was as effective as enalapril 20 to 40 mg/day (both agents could be titrated and combined sequentially with hydrochlorothiazide 25 mg and amlodipine 5 mg). The addition of hydrochlorothiazide to telmisartan was more effective than each agent alone at lowering blood pressure in patients with hypertension. Telmisartan was well tolerated in patients with mild to moderate hypertension and was significantly less likely to cause persistent, dry cough than lisinopril.

CONCLUSION

Telmisartan is an effective antihypertensive agent with a tolerability profile similar to that of placebo. Comparative data have shown telmisartan to be as effective as other major classes of antihypertensive agents at lowering blood pressure. Compared with lisinopril, telmisartan is associated with a significantly lower incidence of dry, persistent cough. Therefore, telmisartan is a useful therapeutic option in the management of patients with hypertension.