Methods

Patients

The study was performed in 24 randomly selected patients (mean age 50 3 years, 10 women) with essential hypertension who were naïve to any antihypertensive treatment. Patients were considered to have sustained hypertension with clinic BP measurements >140/90 mm Hg on three or more occasions and daytime ambulatory BP >135/85 mm Hg. None of the patients were considered to have secondary causes of hypertension on the basis of blood electrolytes, urinary catecholamine (when indicated), and plasma creatinine levels. The ambulant plasma aldosterone (in picomoles per milliliters) and plasma renin activity (in nanograms per milliliters per hour) were determined by commercially available radioimmunoassay (Adaltis Italia SpA, Bologna, Italy) and an ARR of 750 considered abnormal.¹ None were receiving any medication known to cause increased BP (eg, hormonal preparations, oral corticosteroids, nonsteroidal anti-inflammatory drugs). The patients gave informed consent and the study had Institutional Ethics Committee permission.

Study design

After the initial baseline assessment, the patients were randomized in a single-blind crossover design to receive either 50 mg of spironolactone or 2.5 mg of bendroflumetazide for 4 weeks. After a 1-month washout period, the patients were switched to the alternative drug regimen. All the hemodynamic measurements were made in a quiet room, patients having abstained from all caffeine-containing beverages, smoking, and alcohol in the 12 h preceding the study.

Hemodynamic measurements

Blood pressure was measured with an automated digital oscillometric device (Omron Model HEM 705-CP, Omron Corporation, Tokyo, Japan) and a mean of three readings was taken. The radial pressure waveform was derived noninvasively with a high-fidelity strain gauge transducer (SPT-301, Millar Instruments, Houston, TX) and a corresponding aortic pressure waveform generated by using a validated transfer function incorporated in the SphygmoCor (version 6.2, AtCor Medical, Sydney, Australia). The AIx was determined as height of the late systolic peak above the inflection point in the waveform expressed as a percentage of the height of the aortic waveform, which reflects the effect of wave reflections on BP in the aorta, as described previously.^11,12

Pulse wave velocity (PWV) was measured by simultaneous recoding of carotid and femoral artery pressure waveforms by two pressure transducers according to the foot-to-foot method using the Complior device, as described previously¹² (Colson, Dupont Medical, Paris, France). The operator was blind to the form of therapy.

Data analysis

Data were analyzed using JMP version 3.0 (SAS for Windows, Cary, NC). Because the ARR was not normally distributed, it was converted to natural logarithm (in ARR) for further analysis. The relationship between ARR and other biological variables was analyzed using nonparametric Spearman rank correlation coefficients. Due to the repeated nature of the design of the study, the effect of each drug treatment on the hemodynamic parameters was analyzed using a repeated measure analysis of variance. Because the relationship between BP and arterial stiffness is nonlinear, to predict the change in arterial stiffness we adjusted for the decrease in mean BP (covariate) using analysis of covariance. Furthermore, to predict the relationship between ARR and the reduction in mean BP and arterial stiffness (covariates), analysis of covariance was used. Results are expressed as mean SEM, and P < .05 is considered significant.

Results

Table 1 shows the demographic and biochemical parameters of the 24 hypertensive patients. Data on ARR were available only for 22 patients. There was a significant positive correlation between In ARR and aortic systolic BP (r = 0.49, P < .01) (Fig. 1), aortic PP (r = 0.44, P < .01), AIx (r = 0.53, P < .01) (Fig. 2), and negative correlation with pulse pressure (PP) amplification (r = -0.46, P < .05) but not with brachial BP, mean arterial pressure (MAP), or PWV. Six subjects were found to have ARR >750 but none had an adrenal adenoma on magnetic resonance imaging (MRI) scan. The relationship between In ARR, aortic BP, and AIx remained significant when these subjects were excluded from analysis. There was no correlation between these variables and aldosterone or renin alone.

Figure 1.

Correlation between aldosterone-to-renin ratio and aortic systolic blood pressure before treatment (top) and after 1 month of treatment with 50 mg of spironolactone (bottom) in hypertensive patients (n = 24).

Full figure and legend (143K)

Figure 2.

Correlation between aldosterone-to-renin ratio and augmentation index before treatment (top) and after 1 month treatment with 50 mg of spironolactone (bottom) in hypertensive patients (n = 24).

Full figure and legend (130K)

Table 1 - Demographic and biochemical variables in 24 hypertensive subjects (10 women), age 50 (3 years), mean SEM.

Full table

Comparison of spironolactone with bendroflumetazide

Both drugs significantly reduced BP (P < .01); the decrease with spironolactone (mean 16 3/11 1 mm Hg) was significantly greater (P < .01) than that with bendroflumetazide (mean 9 2/6 2 mm Hg), but only spironolactone significantly reduced PWV (P < .001) and AIx (P < .001) and increased PP amplification (P < .05) (Table 2). The reduction in PWV and AIx with spironolactone compared to bendroflumetazide was still statistically significant (P < .01) when corrected for the greater reduction in mean BP with spironolactone.

Table 2 - Hemodynamic changes with 4 weeks of therapy with spironolactone (50 mg) and bendroflumetazide (2.5 mg) in hypertensive subjects (n = 24).

Full table

Relationship of ARR to hemodynamic response to spironolactone

There were positive correlations between ARR and the decrease in brachial systolic BP (r = 0.66, P < .001), aortic systolic BP (r = 0.78, P < .001) (Fig. 1), mean BP (r = 0.75, P < .001), diastolic BP (r = 0.66, P < .001), aortic PP (r = 0.69, P < 0.001), PP amplification (r = 0.46, P < .05), brachial systolic BP (r = 0.66), brachial PP (r = 0.44, P < .05), and AIx (r = 0.64, P < .001) (Fig. 2). Such correlations were also seen with plasma renin but were of lower magnitude—decrease in brachial systolic BP (r = 0.59, P < .005) and aortic systolic BP (r = 0.72, P < .001). There were no significant correlations with plasma aldosterone.

Discussion

Although it has long been accepted that the RAAS is involved in the pathophysiology of hypertension, a consistent relationship between these hormones and BP has not been found,¹³ possibly due to the use of highly labile plasma level of both renin and aldosterone that change with posture, time of day, salt intake, and physical activity. Also, the primary target in looking for an association has focused on the assessment of brachial rather than aortic BP, but recently it has emerged that central or aortic BP is more closely related to cardiovascular risk than brachial or peripheral BP.^11,14 It is now suggested that the ARR may be the more reliable index of "appropriate aldosterone activity."^1,2,3 Our finding that ARR is positively correlated with aortic BP (Fig. 1) and AIx (Fig. 2), suggests an important role for RAAS in the maintenance of aortic BP in essential hypertension. Furthermore, the significant reduction in arterial stiffness with aldosterone antagonism, but not with diuretic therapy, which also positively correlated with the ARR, provides additional evidence to support the hypothesis that aldosterone may have vascular effects in addition to its salt-retaining actions in patients with essential hypertension.

Recent interest in mineralocorticoid hypertension was stimulated by observations on the relative frequency of increased ARR in the hypertensive population and its contribution to "resistant hypertension" and to end-organ damage.⁴ Patients with hyperaldosteronism have greater cardiovascular risk, left ventricular hypertrophy, and end-organ damage.⁶ In essential hypertension, inadequate suppression of aldosterone in response to increased sodium intake is related to both impaired systolic and diastolic function of the left ventricle.¹⁵ Aldosterone may increase vascular collagen and fibrosis, and aldosterone receptors have been found in the aorta.⁶ Aldosterone experimentally increases intramyocardial fibrosis and interstitial and perivascular collagen independent of hypertension⁶ and also increases arterial stiffness in salt-fed rats through change in the elastin and collagen densities, an effect that is prevented by the specific aldosterone antagonist eplerenone.¹⁶ Aldosterone administration produced a significant increase in PP, carotid artery stiffness, and fibronectin, which plays an important role in cell–matrix interactions, in the arterial wall of experimental rats, an effect that was dose-dependently prevented by eplerenone.¹⁶ In the randomised aldactone evaluation study of spironolactone in congestive heart failure, limitation of excessive extracellular matrix turnover, particularly pro-collagen III by spironolactone, appeared to contribute to survival advantage.¹⁷ Primary aldosteronism is also associated with impaired baroreflex function in part related to reduced arterial compliance.¹⁸ Exercise, systolic BP, and the change in systolic BP during exercise were independently related to ARR—a relationship attributed to reduced vascular compliance that impairs the systolic response to exercise.¹³ Not unexpectedly, we found 6 of our 24 untreated patients with essential hypertension to have elevated ARR but no evidence of adrenal adenoma. Excluding these patients from the analysis did not change the significance of our results.

Our finding of a significant positive relationship between ARR and arterial hemodynamics in untreated hypertensive patients was primarily seen with aortic systolic BP (Fig. 1) and PP amplification, both indices of large artery function. The significant relationship with arterial wave reflection, as measured by AIx, further supports this view and compliments the earlier study⁸ showing an effect of aldosterone on carotid artery compliance. Our data now extend these findings showing that during aldosterone antagonism, a very strong relationship exists between ARR and the decrease in aortic systolic BP (r = 0.79; Fig. 1) and AIx (r = 0.64; Fig. 2) and a positive relationship is also seen between ARR and the decrease in brachial systolic BP and mean BP. Such effects were not seen with the hypotensive doses of a thiazide diuretic. After adjustment for the greater antihypertensive effect of spironolactone, the effect on arterial stiffness remains significant. Taken together, these results suggest a role, in part independent of BP reduction, for aldosterone in arterial stiffness. The observation that it is the plasma renin that is driving these relationships to spironolactone response is of interest. Laragh and Sealey⁵ have drawn attention to a group of patients with low renin hypertension who are very sensitive to the antihypertensive effect of spironolactone, which we now confirm in a comparative study with a diuretic. That such patients with the highest ARR, who are most responsive to spironolactone, who have the lowest renin with no evidence of adrenal adenoma, should be considered as primary hyperaldosteronism, is currently the subject of considerable debate.²

Previous data from the 1970s and 1980s on the relationship between renin levels and the response to spironolactone produced contradictory results that may in part be related to methodology of assay and doses studied. The dosages used in this study were based on standard doses, 50 mg of spironolactone as recommended,^1,3,4 in screening for hyperaldosteronism where patients usually exhibit a 20 mm Hg decrease in systolic pressure, and bendroflumetazide, which shows a flat antihypertensive effect at more than 2.5 mg daily. Our data on the comparative antihypertensive efficacy showing a greater effect with spironolactone also needs to be interpreted in the context of duration of therapy. There are data for both drugs that the full effect may not be seen for some months. We chose bendroflumetazide as a comparator because of similar diuretic mode of action and also because it does not have an effect on arterial stiffness.¹²

Cardiovascular risk is related to arterial stiffness assessed by PWV,^19,20 AIx,¹⁰ and aortic BP and PP amplification.¹⁴ We now find a significant relationship between ARR, aortic systolic BP, arterial wave reflection AIx, and PP amplification. The increased effect of wave reflections on the aorta and central arteries causes increased pressure during systole and decreased diastolic BP and diastolic tension-time index.^11,21 These alterations increase left ventricular oxygen requirements and predispose to left ventricular hypertrophy. The reduced diastolic BP contributes to modifications of coronary perfusion with relative subendocardial ischemia.^11,21,22 We did not see a correlation between ARR and PWV, a classic marker of arterial stiffness, at baseline or with the reduction with spironolactone, despite the strong correlation seen with AIx. The AIx is frequently and simplistically considered to be an index of arterial stiffness. However, it depends on many factors, including age, PWV, distance traveled by pressure waves (body height), left ventricular ejection time, and reflective properties of the arterial system. Arterial stiffening increases PWV and influences the transit time of pressure waves. By increasing PWV, arterial stiffening reduces the transit time from the peripheral reflection sites toward central arteries, thereby altering the timing of incident and reflected waves. Although arterial stiffening is responsible for the acceleration of the pressure wave transmission, the intensity of wave reflection is dependent on the reflective properties of the vascular tree, which could be altered independently of arterial stiffening.²³ This independence has also been shown by the persistent association of AIx with increased mortality in patients with end-stage renal disease, independent of PWV.²⁴ The peripheral reflection is influenced by physical properties, vasomotor tone, and the number of smaller resistance arteries and branch points.²³

The finding relating ARR to arterial stiffness is partially in agreement with the recently published study by Resnick et al,²⁵ who demonstrated significant inverse relationships between plasma renin activity and baseline levels of both large and small artery compliance in normotensive subjects and also between basal plasma renin activity values and changes in vascular compliance after angiotensin I receptor antagonism with olmesartan. They found the relationship with small artery compliance (r = 0.43, P < .01) more significant than that with large artery compliance (r = 0.31, P = .03) and in our study, we did not find a significant relationship between ARR and aortic stiffness (PWV). PWV is a more precise measure of large artery stiffness than augmentation index. One might anticipate a functional relationship with the more muscular arteries rather than the elastic aorta in early hypertension. Our subjects were newly diagnosed, never-treated hypertensive patients. The influence of aldosterone on aortic stiffness PWV is more likely to be seen in long-standing hypertension or hyperaldosteronism when aortic wall fibrosis develops. Of note, the earlier study,⁸ which showed a relationship between increased plasma levels of aldosterone and decreased systemic compliance, was in patients with sustained hypertension on long-term therapy, and they used, as in the Resnick study, the classic Windkessel model. The carotid–femoral PWV method is, however, a model independent method for assessing aortic compliance. Although the number of subjects we studied is relatively small, the largest study in this area that measured renin and aldosterone did not find any relationship with PWV in 216 patients with mild-to-moderate essential hypertension.²⁶ However, they found a small number of subjects who carry a variant on the promoter region of the aldosterone synthase gene and have both increased aldosterone and PWV.²⁶

The finding that spironolactone, but not bendroflumetazide, reduced stiffness and the reduction was in part independent of BP reduction is further evidence of a role for ARR in essential hypertension. Also, the stronger correlation between ARR and the reduction in aortic systolic BP and AIx, rather than brachial systolic BP, suggests that the RAAS contributes to increase systolic BP in the aorta by augmenting arterial wave reflection from the periphery. We have similarly found that the conditions associated with arterial stiffness, such as chronic smoking²⁷ or alcohol excess,²⁸ are more marked on aortic than brachial BP. The presence of mineralocorticoid receptors in vascular smooth muscle and endothelial cells provides strong evidence for a local action of aldosterone in the vasculature.^29,30 Potential mechanisms including activation of endothelin, angiotensin II, plasminogen activator inhibitor-1 (PAI-1), transforming-growth factor-1, as well as inhibition of nitric oxide and norepinephrine uptake have been described.^31,32 Blockade of such mechanisms by spironolactone may have contributed to the decrease in both PWV and wave reflection in our study, leading to reduction in wave reflection with a preferential decrease in aortic systolic BP and improvement in PP amplification. Because our study was relatively short (4 weeks) we believe that functional rather than a reversal of structural vascular changes such as fibrosis is likely.

Although the exact mechanisms remain unknown, our results suggest a potential role for aldosterone antagonists preferentially in reducing aortic systolic BP and arterial stiffness, emerging targets in patients with essential hypertension. These findings may also have more immediate therapeutic implications. Hitherto ARR has been used to identify patients with a high ratio (> 750) who may be particularly responsive to spironolactone,³ possibly due to primary hyperaldosteronism. Enhanced responsiveness has now been shown in patients with higher ARR within the normal range—representative of the majority of the hypertensive population. Measurement of ARR may also facilitate the choice of drug therapy in essential hypertension.

References

1. Lim, P. O., Rodgers, P., Cardale, K., Watson, A. D. and MacDonald, T. M. (1999). Potentially high prevalence of primary aldosteronism in a primary care population. Lancet. 353: 40. | Article | PubMed | ChemPort |
2. Padfield, P. L. (2002). Primary aldosteronism, a common entity? The myth persists. J Hum Hypertens. 16: 159–162. | Article | PubMed | ISI | ChemPort |
3. Lim, P. O., Jung, R. T. and MacDonald, T. M. (1999). Raised aldosterone to renin ratio predicts antihypertensive efficacy of spironolactone: a prospective cohort follow-up study. Br J Clin Pharmacol. 48: 756–760. | Article | PubMed |
4. Foo, R., O'Shaughnessy, K. M. and Brown, M. J. (2001). Hyperaldosteronism: recent concepts, diagnosis, and management. Postgraduate Med J. 77: 639–644.
5. Laragh, J. H. and Sealey, J. E. (2003). Relevance of the plasma renin hormonal control system that regulates blood pressure and sodium balance for correctly treating hypertension and for evaluating ALLHAT. Am J Hypertens. 16: 407–415.
6. Schmidt, B. M. W. and Schmieder, R. E. (2003). Aldosterone-induced cardiac damage: focus on blood pressure independent effects. Am J Hypertens. 16: 80–86.
7. Fagard, R. H., Linnen, P. J. and Petrov, V. V. (1998). Opposite associations of circulating aldosterone and atrial natriuretic peptide with left ventricular diastolic function in essential hypertension. J Hum Hypertens. 12: 195–202. | Article |
8. Blacher, J., Amah, G., Girerd, X., Kheder, A., Ben Mais, H., London, G. M. and Safar, M. E. (1997). Association between increased plasma levels of aldosterone and decreased systemic arterial compliance in subjects with essential hypertension. Am J Hypertens. 10: 1326–1334. | Article | PubMed | ISI | ChemPort |
9. Lacolley, P., Safar, M. E., Lucet, B., Ledudal, H. and Benetos, A. (2001). Prevention of aortic and cardiac fibrosis by spironolactone in old normotensive rats. J Am Coll Cardiol. 37: 662–667.
10. Boutouyrie, P., Tropeano, A. I., Asmar, R., Gautier, I., Benetos, A., Lacolley, P. and Laurent, S. (2002). Aortic stiffness is an independent predictor of primary coronary events in hypertensive patients: a longitudinal study. Hypertension. 39: 10–15. | Article | PubMed | ISI | ChemPort |
11. O'Rourke, M. and Staessen, J. A. (2002). Clinical application of arterial stiffness: definitions and reference values. Am J Hypertens. 15: 426–444. | Article | PubMed | ISI |
12. Mahmud, A. and Feely, J. (2002). Effect of angiotensin II receptor blockade on arterial stiffness: beyond blood pressure reduction. Am J Hypertens. 15: 1092–1095. | Article | PubMed | ISI | ChemPort |
13. Lim, P. O., Donnan, P. T. and MacDonald, T. M. (2001). Aldosterone to renin ratio as a determinant of exercise blood pressure response in hypertensive patients. J Hum Hypertens. 15: 119–123. | Article | PubMed |
14. Safar, M. E., Blacher, J., Pannier, B., Guerin, A. P., Marchais, S. J., Guyonvarc'h, P.-M. and London, G. M. (2002). Central pulse pressure and mortality in end-stage renal disease. Hypertension. 39: 735–738. | Article | PubMed | ISI | ChemPort |
15. Schlaich, M. P., Klingbeil, A., Kilger, K., Schobel, H. P. and Schmieder, R. E. (1999). Relation between the renin-angiotensin-aldosterone system and left ventricular structure and function in young normotensive and mildly hypertensive subjects. Am J Hypertens. 138: 810–817.
16. Lacolley, P., Labat, C., Pujol, A., Delcayre, C., Benefit, A. and Safar, M. (2002). Increased carotid wall elastic modulus and fibronectin in aldosterone-salt-treated rats: effects of eplerenone. Circ. 106: 2848–2853.
17. Zannad, F., Alla, F., Dousset, B., Perez, A. and Pitt, B. (2000). Limitation of excessive extracellular matrix turnover may contribute to survival benefit of spironolactone therapy in patients with congestive heart failure. Circ. 102: 2700–2706.
18. Veglio, F., Molino, P., Cat Genova, G., Melchio, R., Rabbia, F., Grosso, T., Martini, G. and Chiandussi, L. (1999). Impaired baroreflex function and arterial compliance in primary aldosteronism. J Hum Hypertens. 13: 29–36. | Article |
19. Blacher, J., Asmar, R., Djane, S., London, G. M. and Safar, M. E. (1999). Aortic pulse wave velocity as a marker of cardiovascular risk in hypertensive patients. Hypertension. 33: 1111–1117. | PubMed | ISI | ChemPort |
20. Laurent, S., Boutouyrie, P., Asmar, R., Gautier, I., Laloux, B., Guize, L., Ducimetiere, P. and Benetos, A. (2001). Aortic stiffness is an independent predictor of all-cause and cardiovascular mortality in hypertensive patients. Hypertension. 37: 1236–1241. | PubMed | ISI | ChemPort |
21. O'Rourke, M. F. and Kelly, R. P. (1993). Wave reflection in the systemic circulation and its implications in ventricular function. J Hypertens. 11: 327–337. | PubMed | ChemPort |
22. Buckberg, G. D., Fixler, D. E., Archie, J. P. and Hoffman, J. I. (1972). Experimental subendocardial ischaemia in dogs with normal coronary arteries. Circ Res. 30: 67–81. | PubMed | ISI | ChemPort |
23. Glasser, S. P., Arnett, D. K. and McVeigh, G. E. (1998). The importance of arterial compliance in cardiovascular drug therapy. J Clin Pharmacol. 38: 202–212.
24. London, G. M., Blacher, J., Pannier, B., Guerin, A. P., Marchais, S. J. and Safar, M. E. (2001). Arterial wave reflections and survival in end-stage renal failure. Hypertension. 38: 434–438. | PubMed | ISI | ChemPort |
25. Resnick, L. M., Catanzaro, D., Sealey, J. E. and Laragh, J. H. (2004). Acute vascular effects of the angiotensin II receptor antagonist olmesartan in normal subjects: relation to the renin-aldosterone system. Am J Hypertens. 17: 203–208.
26. Pojoga, L., Gautier, S., Blanc, H., Guyene, T.-T., Poirier, O., Cambien, F. and Benetos, A. (1998). Genetic determination of plasma aldosterone levels in essential hypertension. Am J Hypertens. 11: 856–860. | Article | PubMed | ChemPort |
27. Mahmud, A. and Feely, J. (2003). Effect of smoking on arterial stiffness and pulse pressure amplification. Hypertension. 41: 183–187. | Article | PubMed | ISI | ChemPort |
28. Mahmud, A. and Feely, J. (2002). Divergent effect of acute and chronic alcohol on arterial stiffness. Am J Hypertens. 15: 240–243. | Article | PubMed | ISI | ChemPort |
29. Hatakeyama, M., Miyamori, I. and Fujita, J. (1994). Vascular aldosterone: biosynthesis and a link to angiotensin-II induced hypertrophy of vascular smooth muscle cells. J Biol Chem. 269: 24316–24320. | PubMed | ISI | ChemPort |
30. Lombes, M., Oblin, M. E., Gasc, J. M., Baulieu, E. E., Farman, N. and Bonvalet, J. P. (1992). Immunohistochemical and biochemical evidence of a cardiovascular mineralocorticoid receptor. Circ Res. 71: 503–510. | PubMed | ISI | ChemPort |
31. Epstein, M. (2001). Aldosterone and the hypertensive kidney: its emerging role as a mediator of progressive renal dysfunction: a paradigm shift. J Hypertens. 19: 829–842. | Article | PubMed | ISI | ChemPort |
32. Stowasser, M. (2001). New perspective on the role of aldosterone excess in cardiovascular disease. Clin Exper Pharmacol Physiol. 28: 783–791.