Improving Prognosis in Hypertension: Exploring the Benefits of Angiotensin II Type 1 Receptor Blockade

Tissue renin angiotensin systems

The RAAS is a powerful regulator of vascular tone and intravascular volume and of tissue architecture and a variety of other functions. The recent appreciation of the immunoregulatory role of angiotensin II and its possible involvement in the genesis of atherosclerosis and in plaque rupture all speak to the wide-ranging physiologic and pathophysiologic activities of the peptide. So do its actions in fat cell differentiation and in neuromodulation. The system exists in the circulation, and RAASs, whole or partial, exist in many tissues. These systems are regulated at many levels ranging from the synthesis of renin to the dimerization of angiotensin receptors. Regulation occurs in multiple tissues and, as a result, tissue concentrations of angiotensin II and the concentration of other RAS components and their active metabolites can vary independently of the circulating system in these tissues. An RAS seems also to function within certain cells. Therapeutic interventions involving ACEIs and ARBs seem likely to provide benefit at least in part through the interruption of local systems. It is to be expected that with enhanced understanding of the biology of the multiple RASs, new suggestions for therapeutic interventions will be forthcoming.

Angiotensin-converting enzyme inhibition in adult hypertensive rats: a stereological study of renal filtration surface area

1. Angiotensin-converting enzyme (ACE) inhibitor treatment leads to beneficial effects on kidney function. The aim of the present study was to determine whether ACE inhibition at high or low doses affects glomerular capillary surface area and length, glomerular number or total renal filtration surface area in rats with established hypertension and, if so, to determine whether these effects are mediated through bradykinin potentiation. 2. Spontaneously hypertensive rats (SHR) were treated with the ACE inhibitor perindopril at either 3 or 0.1 mg/kg per day (high and low doses, respectively) from 16 to 24 weeks of age. Some rats were concomitantly treated with the bradykinin B2 receptor antagonist S16118 (10 nmol/kg per day). Blood pressure was measured twice weekly during the treatment period. At 24 weeks of age, rats were perfusion fixed at 140 mmHg, the kidneys removed, embedded in resin and examined stereologically to estimate glomerular number and volume, length and surface area of glomerular capillaries and total renal filtration surface area. 3. High- and low-perindopril treatment significantly reduced systolic blood pressure compared with control SHR. However, the rats treated with low-dose perindopril were still considered hypertensive. Neither low-dose nor high-dose perindopril treatment had any observable effect on glomerular number (23 876 +/- 1201 vs 26 240 +/- 1465 glomeruli/kidney, respectively) or volume (2.25 +/- 0.21 and 1.96 +/- 0.06 x 10-3 mm3, respectively) compared with controls (glomerular number 25866 +/- 1210 glomeruli/kidney; glomerular volume 2.24 +/- 0.21 x 10-3 mm3). As a result, there was no significant difference in total renal filtration surface area between any of the experimental groups (8161.6 +/- 550.9, 8699.7 +/- 427.6, 9081.9 +/- 453.6, 8830.2 +/- 521.2 and 8559.4 +/- 341.4 mm2 for SHR, SHR low-dose perindopril, SHR low-dose perindopril + B2 antagonist, SHR high-dose perindopril and SHR high-dose perindopril + B2 antagonist, respectively). Coadministration of the bradykinin antagonist had no observable effect on any of the parameters studied. 4. In conclusion, because neither high-dose nor low-dose perindopril had any effect on total renal filtration surface area, the observed beneficial effects of ACE inhibition on kidney function are not the result of enhancement in glomerular capillary surface area.

Valsartan/hydrochlorothiazide: a review of its pharmacology, therapeutic efficacy and place in the management of hypertension

The combination of valsartan [an angiotensin II type 1 (AT(1)) receptor blocker] and hydrochlorothiazide (a thiazide diuretic), administered once daily, has been evaluated in the treatment of patients with hypertension in clinical trials ranging in duration from 8 weeks to 3 years. These studies showed that combination treatment with valsartan 80 or 160mg and hydrochlorothiazide 12.5 or 25mg induced significant reductions from baseline in systolic blood pressure (SBP) and diastolic BP (DBP) in patients with mild to severe hypertension. Clinical trials have demonstrated that the combination of valsartan 80 or 160mg with hydrochlorothiazide 12.5 or 25mg is significantly more effective than either drug alone. Furthermore, valsartan plus hydrochlorothiazide was effective at reducing BP in patients unresponsive to monotherapy with either agent alone. Effective BP control with valsartan plus hydrochlorothiazide was maintained in long-term studies, with reductions observed after 3 months of treatment being similar to those seen after 1, 2 or 3 years. Fixed-dose valsartan/hydrochlorothiazide showed similar BP reductions to amlodipine and to valsartan plus benazepril. Valsartan/hydrochlorothiazide also provided effective 24-hour ambulatory SBP/DBP control. Headache, dizziness and fatigue were the most common adverse events occurring in clinical trials; the incidence of these events in valsartan plus hydrochlorothiazide recipients was not significantly different to that in placebo recipients. Hypokalaemia occurred in 4.5% of valsartan plus hydrochlorothiazide recipients; valsartan attenuated the hydrochlorothiazide-associated decrease in serum potassium concentrations.

CONCLUSIONS

the combination of valsartan and hydrochlorothiazide is an effective treatment for patients with hypertension. Clinical trials have demonstrated that the combination is more effective than either drug alone, and is effective in patients not responding to monotherapy with either agent. Furthermore, the adverse event profile of valsartan/hydrochlorothiazide is similar to that of placebo. Unless there are compelling or specific indications for other drugs, current data support the use of valsartan/hydrochlorothiazide when patients are unresponsive to monotherapy with either agent. Results from clinical trials evaluating the effects of valsartan/hydrochlorothiazide on cardiovascular morbidity and mortality will help to further define the role of the combination in the management of hypertension.

Candesartan cilexetil improves left ventricular function, left ventricular hypertrophy, and endothelial function in patients with hypertensive heart disease

Patients with hypertension often develop left ventricular (LV) hypertrophy and deterioration of the cardiac and endothelial functions. Recent clinical trials have shown the added benefits of angiotensin II receptor blockers in hypertensive patients. Twenty-nine patients with hypertensive heart disease (HHD) underwent echocardiography, radionuclide ventriculography and the measurement of endothelial function before and after administration of candesartan (8 mg/day). The subjects were divided into poorly controlled blood pressure (BP) (group P, n=6) and well controlled BP (group C, n=23). Endothelial function was evaluated from flow-dependent dilation, which was calculated as the percent change of the radial artery diameter during reactive hyperemia after upper arm occlusion, measured with a high-resolution ultrasound system. In group C, LV diastolic function and endothelial function were significantly (p<0.05) improved at 3 months after administration, LV systolic function and hypertrophy were significantly (p<0.05) improved after 6 months and these effects were maintained at 12 months. Even in group P, LV function, LV hypertrophy, endothelial function and brain natriuretic peptide were significantly (p<0.05) improved at 6 months after administration. In patients with HHD, candesartan improves LV systolic and diastolic function, LV hypertrophy and endothelial function within 6 months of administration, regardless of the control of BP.

The clinical implication of tissue renin angiotensin systems

The presence, and in many cases the regulated synthesis, of components of the renin-angiotensin system have been demonstrated in multiple tissues, indicating the existence of tissue angiotensin-generating systems. These vary with respect to which renin-angiotensin system components are synthesized locally and which are taken up from plasma. Enzymes unrelated to the classical renin-angiotensin system may also contribute to tissue angiotensin synthesis. However, based on the available data, the prevailing opinion that kidney-derived renin is in all cases the only physiologically relevant renin in tissues must be revised. Also there is evidence indicating a role for tissue angiotensin systems in the pathogenesis of cardiovascular disease and in cardiovascular structural remodeling. The angiotensin-regulated synthesis of aldosterone in cardiac tissue has been described, suggesting the possibility that a renin-angiotensin-aldosterone system exists in the heart. In addition, intracellular (intracrine) sites of angiotensin action have been reported. Some of these findings have implications for therapeutics and, in particular, for the use of angiotensin converting-enzyme inhibitors and angiotensin receptor blockers. Finally, tissue angiotensin systems outside the cardiovascular system also appear to be physiologically relevant.