Volume 5, Number 2, June 2004

POPULAR
TOPICPAPERA putative placebo comparison of the SCOPE and LIFE trials
Peter A Meredith, Lilian S Murray, John JV McMurray

The Losartan Intervention For Endpoint reduction in hypertension (LIFE) trial and the Study on Cognition and Prognosis in the Elderly (SCOPE) superficially produced comparable outcomes, with effects on stroke greater than those anticipated from blood pressure (BP) lowering alone. This, however, ignores important features of both studies. It ignores firstly the disparate comparator agents – atenolol in LIFE and predominantly hydrochlorthiazide in SCOPE, secondly the small, but potentially important BP differential between the treatment arms in SCOPE and finally the small, statistically non-significant increase in coronary heart disease (CHD) in both trials. This analysis compares the major cardiovascular outcomes in these trials with reference to placebo. Two alternative reference populations were employed to calculate the imputed placebo, firstly the MRC Trial in Elderly Hypertensives and secondly a meta-analysis of trials in the elderly, which included comparisons between diuretic- and b-blocker-based regimens. Overall, the choice of ‘comparator placebo’ did not substantially influence the derived results. Accounting for BP differences and based on the meta-analysis, both trials demonstrated statistically significant reductions in fatal/non-fatal stroke compared with placebo – relative risks (95% confidence intervals [CI]) of 0.53 (0.39, 0.73) and 0.56 (0.41, 0.76) for SCOPE and LIFE, respectively. For fatal/non-fatal MI, there were greater discrepancies between the studies, but with neither achieving statistical significance compared with placebo – relative risks of 0.85 (0.59, 1.24) and 1.08 (0.80, 1.46) for SCOPE and LIFE, respectively. This analysis clearly demonstrates that both candesartan in SCOPE and losartan in LIFE are associated with reductions in stroke events compared with placebo, greater than that observed in the well-established meta-analysis of placebo-controlled hypertensive trials. However, the CIs are such that it is not possible to suggest definitively that this is a benefit beyond BP reduction alone. Neither trial is sufficiently ‘powered’ to demonstrate a benefit in CHD outcomes, but with SCOPE there was a trend towards benefit with a point estimate compatible with the major meta-analysis.

JRAAS 2004;5:59-63.

POPULAR
TOPICPAPEREffect of candesartan and lisinopril alone and in combination on blood pressure and microalbuminuria
Trefor Morgan, Adrianne Anderson, Denise Bertram, Robert Jeffrey MacInnis

Background: Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blocking drugs (ARB) block the effect of angiotensin II by different mechanisms. It has been suggested that combined therapy may be more effective at reducing blood pressure (BP) than higher doses of either drug.
Methods: Twenty-three elderly patients with systolic hypertension completed a double-blind crossover study comparing placebo, candesartan (C) 16 mg, C32 mg, lisinopril (L) 20 mg, L40 mg and C16 mg + L20 mg. Treatment periods were one month and ambulatory BP measurements were performed at the end of each period. The effects on albumin excretion in eight patients with microalbuminuria were determined.
Results: All treatments lowered BP. The falls in systolic and diastolic BP with C16, C32, L20 and L40 were similar. Plasma renin rose to a similar extent. A plateau effect was reached with C16 and L20. Systolic BP on the combination of C16 + L20 was lower than on each monotherapy (C16, 3.8 mmHg [p=0.002]; C32, 6.4 [0.0003]; L20, 2.9 [0.05]; L40, 3.3 [0.003]). The additional fall in BP with the combination appeared to be due to recruitment of non-responders, rather than to an additive effect in most patients. All treatments reduced microalbuminuria to a similar extent. The combination was well tolerated and there was no deterioration in renal function.
Conclusion: When patients are on a plateau dose of an ACE inhibitor or an ARB, addition of the other drug class has a small but significant incremental effect on BP in the overall group. However, some patients respond better to one drug class than to the other and this may explain the results. This study lends no support to the use of these two drugs in combination to treat hypertension.

JRAAS 2004;5:64-71.

PAPERMacroarray analysis in the hypertrophic left ventricle of renin-dependent hypertensive rats: identification of target genes for renin
Mazen Kurdi, Catherine Cerutti, Jacques Randon, Lilian McGregor, Giampiero Bricca

Introduction: The aim of this work was to identify new renin target genes in left ventricular hypertrophy during hypertension.
Materials and methods: We compared left ventricle gene expression from four transgenic TGR(mRen2)27 (TG+/-) rats and four non-transgenic littermates (TG-/-) using cDNA macroarray. Hybridisation signals were quantified with a phosphorimager, and normalised to an external scale. Data analysis was performed with Statistical Analysis for Microarrays (SAM 1.21) software. The mRNA levels of candidate genes were determined by semi-quantitative RT-PCR in three different hypertensive rats: TG+/-, spontaneously hypertensive (SHR) and genetically Lyon hypertensive (LH) rats, compared to their respective controls (TG-/-, Wistar-Kyoto, Lyon low blood pressure rats).
Results: Out of 1,200 genes present on the macroarray, 233 were reliably measured and only three were overexpressed (Biglycan, β1-adenosine monophosphate-activated protein kinase [AMPK] and amyloid precursor like protein 2 [APLP2]) and 19 were underexpressed in the left ventricle of TG+/- compared with TG-/-. APLP2 is a member of the amyloid precursor protein (APP) family. APLP2 and APP mRNA levels were increased in TGR(mRen2)27 but significantly decreased in LH rats, while only APP was increased in SHR rats.
Conclusions: We report new genes associated with renin-dependent left ventricular hypertrophy. Moreover, this work shows for the first time that the APP family gene expression could be altered in response to high renin activity and this effect is independent of cardiac remodelling and hypertension.

JRAAS 2004;5:72-78.

PAPERComparative study of the inhibitory effects of adrenomedullin on angiotensin II contraction in rat conductance and resistance arteries
Ion Haulica, Walther Bild, Christian Mihaila, Dragomir N Serban, Lacramioara Serban, Daniela Boisteanu, Teodor Ionita, Oana Radasanu

Adrenomedullin (ADM), a ubiquitous vasoactive peptide, has been the target of a multitude of studies concerning its effect on the vascular tone. The present work aims at clarifying a series of its interactions with the renin-angiotensin system. The study uses the rat aorta ring as a model of conductance vessels, with or without vascular endothelium, and the second order branch of rat mesenteric arteries as a model of resistance arteries.
Interactions between various concentrations of ADM and angiotensin II (Ang II) were studied, in the presence of L-NAME (a nitric oxide [NO] synthase inhibitor) and methylene blue (MB; a soluble guanylate cyclase inhibitor).
Results point out differences in the mechanism of the inhibitory action of ADM upon Ang II effects in the two vessel types studied. Inhibition of Ang II contraction by ADM involves guanylate cyclase in both cases. However, NO is involved in ADM-induced inhibition of angiotensinergic vasoconstriction only in the conductance arteries, not in the resistance ones.

JRAAS 2004;5:79-83.

PAPERTonic levels of angiotensin II reduce tonic levels of vascular nitric oxide even in salt-replete man
Justein SN Sim, Colin Farquharson, Allan D Struthers

Introduction: Losartan improves stimulated endothelial function in patients with cardiovascular disease, but there are no data to establish whether losartan has this effect in normal man. Furthermore, whether losartan improves basal nitric oxide (NO) activity is controversial. We therefore examined whether treatment with losartan improved basal NO activity in normal, salt-replete man. If so, this would imply that tonic levels of angiotensin II (Ang II) reduce tonic basal levels of NO, even in salt-replete normal man.
Methods: We performed a randomised, placebo-controlled, double-blind crossover study in 24 healthy volunteers, comparing losartan 50 mg daily for one month versus placebo. Brachial artery endothelial function was assessed by bilateral venous occlusion plethysmography, measuring the response to intra-arterial infusions of the endothelial-dependent and endothelial-independent vasodilators, acetylcholine and sodium nitroprusside respectively and the endothelial-dependent vasoconstrictor NG-monomethyl-L-arginine. Results were analysed by multiple analysis of variance and statistical significance was taken as a p value of < 0.05.
Results: Losartan significantly increased the vasoconstriction in response to NG-monomethyl-L-arginine (-37+2% vs. -32+2%, losartan vs. placebo; p=0.05). Losartan improved the vasodilatation response to acetylcholine; however, this result did not reach significance (214+20% vs. 174+20%, losartan vs. placebo; p=0.15). Losartan did not affect the response to nitroprusside (172+15% vs. 176+16%, losartan vs. placebo; p=0.84). There was no significant difference in blood pressure between the two study days.
Conclusions: Losartan improves basal NO bioactivity in healthy salt-replete volunteers. Even in salt-replete man, basal Ang II levels exert a tonic effect, which reduces basal NO.

JRAAS 2004;5:84-88.

PAPERRegulation of renal proximal fluid uptake by luminal and peritubular angiotensin II
Siriphun Hiranyachattada, Peter J Harris

Introduction: Angiotensin II (Ang II), when administered to either tubular lumen or peritubular capillary, exerts a biphasic action on proximal fluid uptake rate. At low concentrations, (10^-12–10^-10 M) Ang II stimulates fluid transport, whereas higher doses (>10^-9 M) inhibit. Ang II is secreted into the lumen in the proximal tubule and the concentration of Ang II in the proximal lumen has been reported to be in the nanomolar range, 100–1,000 times higher than in peritubular blood. We investigated the regulation of renal proximal fluid transport by luminal (predominantly locally produced) and peritubular capillary (circulatory) Ang II in anaesthetised rats, using a selective AT₁-receptor antagonist, candesartan.
Methods: Experiments were performed in inactin-anaesthetised male Wistar rats. Proximal fluid uptake rate was measured using computerised capture and analysis of shrinking-split droplet microperfusion in response to either luminal addition or luminal addition with simultaneously peritubular capillary perfusion of 10^-8 M candesartan.
Results: Luminal addition of candesartan (10^-8 M) decreased fluid absorption by 19–25%. Perfusion of the peritubular capillaries with an electrolyte solution (containing no Ang II) reduced fluid uptake by 27%, and blockade of the peritubular actions of Ang II by addition of candesartan (10-8 M) resulted in 33% decrease in fluid uptake. However, when candesartan (10^-8 M) was added to both luminal and capillary perfusates, there was a 43% reduction in fluid transport when compared with initial values.
Conclusion: These results suggest that the presence of endogenous Ang II in both peritubular blood and luminal fluid is important for maximal expression of the stimulatory influence of this peptide on proximal tubule fluid uptake.

JRAAS 2004;5:89-92.

POPULAR
TOPICPAPERLosartan may prevent the elevation of plasma glucose, corticosterone and catecholamine levels induced by chronic stress
Yagiz Üresin, Bahar Erbas, Mehmet Özek, Elif Özkök, Ali Osman Gürol

Introduction: Stress is a stimulus that activates the hypothalamic pituitary adrenal (HPA) axis and sympathetic nervous system (SNS). Increased activity of the SNS causes to increment or impairment in blood pressure, heart rate, body temperature and plasma glucose and adreno- corticotrophic hormone (ACTH) levels. Angiotensin II (Ang II), which is a product of the renin-angiotensin system (RAS), is an important factor affecting the activity of the SNS and responses to stress. We suggest that the blockade of Ang II may be worthwhile in the prevention and treatment of diabetes mellitus and cardiovascular diseases affected by stress. Therefore, we investigated the effects of immobilisation stress on blood glucose, norepinephrine (NE), epinephrine (E) and corticosterone levels and the effects of an Ang II receptor antagonist, losartan, on these parameters.
Materials and methods: The rats were kept in small cylindrical cages for 60 min/day for 10 consecutive days to perform chronic immobilisation stress. Losartan (10 mg/kg) was given daily by gavage to Losartan (L) and Losartan + Chronic Stress (L+CS) groups. Control (C) and Chronic Stress (CS) groups received an equal volume of saline daily by gavage for 10 days. After the last stress regimen, blood samples were collected for plasma glucose, NE, E and corticosteroid measurements.
Results: Plasma glucose, NE, E and corticosterone levels in the CS Group increased significantly compared with the C group. In Group L+CS, the plasma glucose, NE, E and corticosterone levels decreased significantly vs. Group CS. In Group L there was no significant difference vs. Group C.
Conclusion: It can be speculated that chronic blockade of RAS may decrease the excess sympathetic responses to stress in cardiovascular diseases and prevent the likely development of Type II diabetes mellitus.

JRAAS 2004;5:93-96.

EDITORIAL REVIEWOligomerisation of angiotensin receptors: novel aspects in disease and drug therapy
Liza Barki-Harrington

The concept that 7 transmembrane receptors (7TMRs) exist and function as independent monomers has facilitated a therapeutic approach of selective targeting of receptors. However, oligomerisation of 7TMRs is now being recognised as an important biological phenomenon that adds a level of complexity to their signalling. In vitro, many 7TMR heterodimers display altered binding, signalling, and trafficking properties compared to their constituent monomeric units. This review discusses an emerging concept regarding the role of 7TMR heterodimerisation in vivo, and its significance to drug therapy. Studies of angiotensin receptor signalling indicate a pivotal role for heterodimerisation in the pathogenesis of human disorders. Furthermore, the occurrence of angiotensin receptor heterodimers has a profound effect on the responsiveness to treatment with 7TMR blockers. Global assessment of the prevalence of different heterodimers during disease and their responsiveness to drug therapy is likely to optimise patient treatment and reduce side-effects associated with 7TMR blockers.

JRAAS 2004;5:49-52.

POPULAR
TOPICEDITORIAL REVIEWThe utility of BNP in clinical practice
Andrew Sharp, Jamil Mayet

Brain natriuretic peptide (BNP) is a cardiac neurohormone of increasing interest over recent years, with research applications expanding at a rapid rate and new data published on a monthly basis. Initially developed as a diagnostic aid for those with acute shortness of breath, clinical applications are now increasing, and this article reviews these clinical applications of BNP and the evidence for effectiveness of the synthetic BNP analogue nesiritide.

JRAAS 2004;5:53-58.