Effects of diuretic therapy in low-, normal- and high-renin isolated systolic systemic hypertension

Microbial short chain fatty acid metabolites lower blood pressure via endothelial G protein-coupled receptor 41

Short chain fatty acid (SCFA) metabolites are byproducts of gut microbial metabolism that are known to affect host physiology via host G protein-coupled receptor (GPCRs). We previously showed that an acute SCFA bolus decreases blood pressure (BP) in anesthetized mice, an effect mediated primarily via Gpr41. In this study, our aims were to identify the cellular localization of Gpr41 and to determine its role in BP regulation. We localized Gpr41 to the vascular endothelium using RT-PCR: Gpr41 is detected in intact vessels (with endothelium) but is absent from denuded vessels (without endothelium). Furthermore, using pressure myography we confirmed that SCFAs dilate resistance vessels in an endothelium-dependent manner. Since we previously found that Gpr41 mediates a hypotensive response to acute SCFA administration, we hypothesized that Gpr41 knockout (KO) mice would be hypertensive. Here, we report that Gpr41 KO mice have isolated systolic hypertension compared with wild-type (WT) mice; diastolic BP was not different between WT and KO. Older Gpr41 KO mice also exhibited elevated pulse wave velocity, consistent with a phenotype of systolic hypertension; however, there was no increase in ex vivo aorta stiffness (measured by mechanical tensile testing). Plasma renin concentrations were also similar in KO and WT mice. The systolic hypertension in Gpr41 KO is not salt sensitive, as it is not significantly altered on either a high- or low-salt diet. In sum, these studies suggest that endothelial Gpr41 lowers baseline BP, likely by decreasing active vascular tone without altering passive characteristics of the blood vessels, and that Gpr41 KO mice have hypertension of a vascular origin.

Personalizing the diuretic treatment of hypertension: the need for more clinical and research attention

Neither randomized controlled trials nor efforts to identify genetic markers have been helpful with regard to the goal of individualizing diuretic therapy in the treatment of hypertension, a goal that receives little clinical or research attention. This review will examine, and bring attention to, the considerable yet overlooked information relevant to individualizing diuretic therapy. It will bring attention to clinical, biochemical, and pharmacological clues that can be helpful in identifying who is likely to respond to a diuretic, who needs a stronger diuretic regimen, which diuretic to prescribe, and how to minimize adverse effects. New directions for clinical research aimed at individualizing use in hypertension will be explored. Research and clinical attention to the goal of individualizing diuretic treatment in hypertension need to be renewed, to help us achieve greater hypertension control with fewer adverse effects and lower costs.

Association between aldosterone production and variation in the 11beta-hydroxylase (CYP11B1) gene

CONTEXT

Variation in the region of chromosome 8 including the genes steroid 11beta-hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2) influences mineralocorticoid and glucocorticoid metabolism. However, the relative importance of polymorphisms in CYP11B1 and CYP11B2 in determining these phenotypes is unknown.

OBJECTIVE

Our objective was to investigate genetic influences of the CYP11B1 and CYP11B2 genes on mineralocorticoid metabolism.

DESIGN

We measured 24-h urinary excretion of the key metabolites of the principal mineralocorticoids, glucocorticoids and androgens secreted by the adrenal cortex. We genotyped polymorphisms spanning the CYP11B1 and CYP11B2 genes, which together capture all common variations at the locus.

PARTICIPANTS

Participants included 573 members of 105 British Caucasian families ascertained on a hypertensive proband.

MAIN OUTCOME MEASURES

We assessed heritability of urinary tetrahydroaldosterone (THAldo) excretion and association of THAldo excretion with genotype.

RESULTS

The heritability of THAldo excretion was 52% (P < 10(-6)). There was significant association between THAldo and genotype at several of the CYP11B1/B2 polymorphisms. The strongest association was observed at the rs6387 (2803A/G) polymorphism in intron 3 of CYP11B1 (P = 0.0004). Association followed a codominant model with a 21% higher THAldo excretion per G allele. Genotype at rs6387 accounted for 2.1% of the total population variability of THAldo. We found significant association between THAldo excretion and urinary total androgen excretion, urinary tetrahydrodeoxycortisol level, and urinary cortisol metabolites (all P < 0.001).

CONCLUSIONS

Aldosterone synthesis is highly heritable and is affected by genotype at CYP11B1. Our findings support the hypothesis that genetically determined differences in 11-hydroxylation efficiency can have downstream effects on mineralocorticoid synthesis. Such effects may be of relevance to the development of low-renin essential hypertension.

Syst-Eur. A multicentre trial on the treatment of isolated systolic hypertension in the elderly: objectives, protocol, and organization

The Syst-Eur Trial is a concerted action of the European Community's Medical and Health Research Programme. The trial is carried out in consultation with the World Health Organization, the International Society of Hypertension, the European Society of Hypertension and the World Hypertension League. This article describes the objectives and the protocol of Syst-Eur, a multicentre trial designed by the European Working Party on High Blood Pressure in the Elderly (EWPHE), to test the hypothesis that antihypertensive treatment of elderly patients with isolated systolic hypertension results in a significant change in stroke morbidity and mortality. Secondary endpoints include cardiovascular events, such as myocardial infarction and congestive heart failure. To be eligible patients must be at least 60 years old and have a systolic blood pressure averaging 160-219 mmHg with a diastolic pressure less than 95 mmHg. Patients must give their informed consent and be free of major cardiovascular and non-cardiovascular diseases at entry. The patients are randomized to active treatment or placebo. Active treatment consists of nitrendipine (10-40 mg/day), combined with enalapril (5-20 mg/day) and hydrochlorothiazide (12.5-25 mg/day), as necessary. The patients of the control group receive matching placebos. The drugs (or matching placebos) are stepwise titrated and combined in order to reduce systolic blood pressure by 20 mmHg at least to a level below 150 mmHg. Morbidity and mortality are monitored to enable an intention-to-treat and per-protocol comparison of the outcome in the 2 treatment groups. A one-year pilot trial (1989) showed that the protocol is practicable. The Ethics Committee therefore decided to start the definite study (1990), in which randomized patients will be followed for 5 years. Recruitment of new centres and of the required 3,000 patients will last 3 years (until 1993).

Isolated systolic hypertension: declining prevalence in the elderly

Isolated systolic hypertension is a prevalent condition among elderly U.S. residents of all age, sex, and race groups. In a population-based survey conducted on 4,672 adult residents of Georgia in 1981, prevalence rates were considerably below those noted in earlier surveys, such as Baldwin County, Georgia (1962), National Health Examination Series I (1960-1962), Evans County, Georgia (1967-1969), National Health and Nutrition Examination Survey I (1971-1974) and/or II (1976-1980). The lower 1981 prevalence of isolated systolic hypertension in Georgia was observed in association with a much greater likelihood of anti-hypertensive therapy in adult and elderly patients. The overall trend for early and more aggressive therapy of diastolic hypertension might account for less arterial rigidity and occurrence of isolated systolic hypertension in later life.

Systemic systolic hypertension in the elderly: correlation of hemodynamics, plasma volume, renin, aldosterone, urinary metanephrines and response to thiazide therapy

Twenty-four men, mean age 63 +/- 1.7 years, with systemic systolic hypertension were studied before and after 1 month of therapy with oral hydrochlorothiazide, 50 mg/day. The control mean plasma volume was 2,664 +/- 96 ml, cardiac index 3.9 +/- 0.2 liters/min/m2, stroke volume index 52 +/- 2 ml/beat/m2, systemic vascular resistance 1,351 +/- 80 dynes s cm-5, plasma aldosterone 8.6 +/- 1.0 ng/dl and 24-hour urinary excretion of metanephrines 0.371 +/- 0.044 mg. On renin-sodium profiling in 23 patients, 12 were classified into a normal group and 11 into a low-renin group; none had high renin values. Based on multiple regression analysis, the 24-hour urinary excretion of total metanephrines appeared to be the single most important factor explaining 28% of the variability in systolic blood pressure (BP). After therapy with oral hydrochlorothiazide, the elevated systolic BP decreased (p less than 0.0001) and diastolic BP decreased (p less than 0.005), with concomitant reduction in systemic vascular resistance (p less than 0.03). Patients in both the normal- and low-renin groups had normal plasma volume and responded similarly to thiazide diuretic therapy, without symptomatic side effects.

Comparison of the effects of diuretic therapy and low sodium intake in isolated systolic hypertension

Of 103 patients with isolated systolic hypertension, 71 were treated with diuretics and another 32 with low-sodium diet. In the 71 who were treated with diuretics, body weight decreased from 69.48 +/- 1.47 to 68.60 +/- 1.45 kg (p less than 0.0005) and systolic blood pressure from 178 +/- to 152 +/- 2 mm Hg (p less than 0.0005). Plasma renin activity increased from 1.78 +/- 0.30 to 7.32 +/- 1.78 ng/ml per hour (p less than 0.005) and urinary aldosterone from 10 +/- 1 to 23 +/- 4 micrograms per 24 hours (p less than 0.005). The greatest decrease in systolic blood pressure occurred in patients in the low-renin group (-32 +/- 2 mm Hg), whereas it decreased by 24 +/- 2 mm Hg (p less than 0.04) in the normal-renin group; however, blood pressure did not change significantly in the high-renin group. In the 32 patients who were treated with low-sodium diet, the 24-hour urinary sodium excretion decreased from 143 +/- 10 to 48 +/- 5 meq (p less than 0.005), body weight decreased from 71.18 +/- 2.50 to 70.17 +/- 2.47 kg (p less than 0.005), systolic blood pressure decreased from 174 +/- 2 to 156 +/- 3 mm Hg (p less than 0.0005), and diastolic blood pressure decreased from 90 +/- 1 to 87 +/- 1 mm Hg (p less than 0.01). Plasma renin activity increased from 2.25 +/- 0.33 to 4.27 +/- 0.43 ng/ml per hour (p less than 0.005) and urinary aldosterone from 9 +/- 1 to 15 +/- 2 micrograms per 24 hours (p less than 0.005). The decrease in the systolic blood pressure was related to the pretreatment 24-hour urinary sodium excretion (r = 0.40, p less than 0.05). The smallest decrease in systolic blood pressure occurred in the patients with high renin values (-1 +/- 9 mm Hg, n = 5), whereas the decrease in systolic blood pressure in the low-renin (n = 12) and normal-renin groups (n = 15) was similar, -22 +/- 2 mm Hg and -21 +/- 3 mm Hg, respectively (p less than 0.005 compared with the high-renin group). These results indicate that both diuretic therapy and low-sodium diet are effective antihypertensive means in most patients with isolated systolic hypertension and low or normal plasma renin activity.

Renin dependency of blood pressure in isolated systolic hypertension

The role of the renin system in the maintenance of the elevated systolic blood pressure in isolated systolic hypertension was investigated in 31 patients who received long-term treatment with propranolol (120 mg daily) and in another group of 22 patients with isolated systolic hypertension who received a test dose of captopril (25 or 50 mg). The greatest systolic blood pressure decrease (35 +/- 5 mm Hg) by propranolol occurred in the high-renin group (n = 9), and the smallest decrease (3 +/- 2 mm Hg) in the low-renin group (n = 9), whereas in the normal-renin group (n = 13), systolic blood pressure was decreased by propranolol by 22 +/- 5 mm Hg. For all the propranolol-treated patients, the decrement in the systolic blood pressure by propranolol was related to the control plasma renin activity (r = 0.63, p less than 0.01) and to the concurrent change in plasma renin activity (r = 0.70, p less than 0.001). Captopril decreased the systolic blood pressure by 55 +/- 10 mm Hg in the high-renin group (n = 11) and by 17 +/- 5 mm Hg in the normal-renin group (n = 6), whereas the smallest decrease (12 +/- 5 mm Hg) in systolic blood pressure occurred in the low-renin group (n = 5). In all the captopril-tested patients (n = 22), the decrease in systolic blood pressure by captopril was related to the control plasma renin activity (r = 0.75, p less than 0.001). These results indicate that the plasma renin activity value indicates the participation of the renin-angiotensin system in the maintenance of the elevated systolic blood pressure in patients with isolated systolic hypertension.