Characterization of Potassium-Induced Natriuresis in Hypertensive Postmenopausal Women During Both Low and High Sodium Intake

BACKGROUND

Potassium-induced natriuresis may contribute to the beneficial effects of potassium on blood pressure but has not been well-characterized in human postmenopausal hypertension. We determined the time course and magnitude of potassium-induced natriuresis and kaliuresis compared with hydrochlorothiazide in 19 hypertensive Hispanic postmenopausal women. We also determined the modulating effects of sodium intake, sodium-sensitivity, and activity of the thiazide-sensitive NCC (sodium-chloride cotransporter).

METHODS

Sixteen-day inpatient confinement: 8 days low sodium followed by 8 days high sodium intake. During both periods, we determined sodium and potassium excretion following 35 mmol oral KCl versus 50 mg hydrochlorothiazide. We determined sodium-sensitivity as change in 24-hour systolic pressure from low to high sodium. We determined NCC activity by standard thiazide-sensitivity test.

RESULTS

Steady-state sodium intake was the key determinant of potassium-induced natriuresis. During low sodium intake, sodium excretion was low and did not increase following 35 mmol KCl indicating continued sodium conservation. Conversely, during high sodium intake, sodium excretion increased sharply following 35 mmol KCl to ≈37% of that produced by hydrochlorothiazide. Under both low and high sodium intake, 35 mmol potassium was mostly excreted within 5 hours, accompanied by a sodium load reflecting the steady-state sodium intake, consistent with independent regulation of sodium/potassium excretion in the human distal nephron.

CONCLUSIONS

Potassium-induced natriuresis was not greater in sodium-sensitive versus sodium-resistant hypertensives or hypertensives with higher versus lower basal NCC activity. We studied an acute KCl challenge. It remains to further characterize potassium-induced natriuresis during chronic potassium increase and when potassium is administered a complex potassium-containing meal.

Thiazide-Sensitive NCC (Sodium-Chloride Cotransporter) in Human Metabolic Syndrome: Sodium Sensitivity and Potassium-Induced Natriuresis

The thiazide-sensitive sodium-chloride cotransporter (NCC;SLC12A3) is central to sodium and blood pressure regulation. Metabolic syndrome induces NCC upregulation generating sodium-sensitive hypertension in experimental animal models. We tested the role of NCC in sodium sensitivity in hypertensive humans with metabolic syndrome. Conversely, oral potassium induces NCC downregulation producing potassium-induced natriuresis. We determined the time course and magnitude of potassium-induced natriuresis compared with the natriuresis following hydrochlorothiazide (HCTZ) as a reference standard. We studied 19 obese hypertensive humans with metabolic syndrome during 13-day inpatient confinement. We determined sodium sensitivity by change in 24-hour mean systolic pressure by automated monitor from days 5 (low sodium) to 10 (high sodium). We determined NCC activity by standard 50 mg HCTZ sensitivity test (day 11). We determined potassium-induced natriuresis following 35 mmol KCl (day 13). We determined (1) whether NCC activity was greater in sodium-sensitive versus sodium-resistant participants and correlated with sodium sensitivity and (2) time course and magnitude of potassium-induced natriuresis following 35 mmol KCl directly compared with 50 mg HCTZ. NCC activity was not greater in sodium-sensitive versus sodium-resistant humans and did not correlate with sodium sensitivity. Thirty-five-millimoles KCl produced a rapid natriuresis approximately half that of 50 mg HCTZ with a greater kaliuresis. Our investigation tested a key hypothesis regarding NCC activity in human hypertension and characterized potassium-induced natriuresis following 35 mmol KCl compared with 50 mg HCTZ. In obese hypertensive adults with metabolic syndrome ingesting a high-sodium diet, 35 mmol KCl had a net natriuretic effect approximately half that of 50 mg HCTZ.

Hypertension in the frail elderly

Extant data indicate that treating to lower systolic pressure confers significant advantage to younger people in general good health and to relatively healthy octogenarians. Few data exist to guide practitioners on the treatment of frail elderly hypertensives. Chronological age alone does not suffice to make useful judgments regarding therapy. The definition of frailty remains controversial. One method, use of a simple questionnaire or a test of walking speed is practical but not universally accepted. Frail subjects, while at higher risk for cardiovascular complications, seem to benefit less or not at all from antihypertensive drug treatment. Clinicians should treat robust older patients as they would younger patients because the benefits far outweigh the low risk of adverse effects. Successful antihypertensive therapy in those younger than 80 years should not be discontinued simply because that age milestone has been crossed. Treatment of frail older patients must be individualized. Some frail survivors age 80 years or older may actually fare better with elevated systolic pressures. Pending the cognitive function substudy of Systolic Blood Pressure Intervention Trial, there is little evidence that antihypertensive treatment benefits established cognitive dysfunction. Because hypertension in middle age is a good predictor of later cognitive dysfunction, the clinical approach should be one of early prevention.

Management of hypertension in hospitalized patients

Elevated blood pressure (BP) is a common problem in patients hospitalized for reasons other than hypertension. Unexpected elevations commonly result in calls to physicians who too often prescribe medication to reduce the numbers without evaluating the patient or determining the cause of the elevation. This may result in unnecessary and sometimes harmful treatment. Such BP elevation has many potential causes. These include anxiety, post-operative salt and volume overload, failure to administer the patient's known antihypertensive medication, inability to give oral antihypertensive medication to patients who cannot take pills by mouth, incipient heart failure, previously unrecognized renal failure, obstructive uropathy and other causes. These must be identified and treated prior to addressing only the elevated BP numbers. We present an algorithm for evaluating hospitalized patients with elevated BP in order to assist physicians in identifying the true cause of the elevation, treating the identified cause, and giving appropriate drug treatment. We also note that this is a golden opportunity for communication with the outpatient providers who will follow the patient.

Inherent inaccuracies and potential utility of race/ethnicity labeling in the treatment of hypertension

The use of racial/ethnic labeling for any purpose is fraught with substantial emotional, social and political consequences even when used for demographic studies or census. In addition to the very real historical conflicts associated with slavery in the Americas and various social classification systems elsewhere, such labeling has been shown by the use of ancestral identification markers to be inaccurate in many cases. Even geographic labeling, such as East Asians, ignores the marked heterogeneity of East Asians. The use of race alone to determine selection of initial antihypertensive therapy is a very limited approach. The Department of Veterans Affairs Cooperative Study Group on Antihypertensive Agents has demonstrated, however, that the use of age and race together may be a useful paradigm for predicting response to a single antihypertensive drug. Furthermore, individuals from populations who consume high levels of sodium and lower levels of potassium may respond better to diuretics and calcium antagonists. Other populations may be more susceptible to angioedema or cough related to the use of angiotensin-converting enzyme inhibitors. Such information may be useful for the selection or avoidance of certain medications. No patient should ever be denied indicated treatment with a drug or drug class because of race or ethnicity.

ASH position paper: dietary approaches to lower blood pressure

A substantial body of evidence has implicated several aspects of diet in the pathogenesis of elevated blood pressure (BP). Well-established risk factors for elevated BP include excess salt intake, low potassium intake, excess weight, high alcohol consumption, and suboptimal dietary pattern. African Americans are especially sensitive to the BP-raising effects of excess salt intake, insufficient potassium intake, and suboptimal diet. In this setting, dietary changes have the potential to substantially reduce racial disparities in BP and its consequences. In view of the age-related rise in BP in both children and adults, the direct, progressive relationship of BP with cardiovascular-renal diseases throughout the usual range of BP, and the worldwide epidemic of BP-related disease, efforts to reduce BP in nonhypertensive as well as hypertensive individuals are warranted. In nonhypertensives, dietary changes can lower BP and delay, if not prevent, hypertension. In uncomplicated stage I hypertension, dietary changes serve as initial treatment before drug therapy. In hypertensive individuals already on drug therapy, lifestyle modifications can further lower BP. The current challenge is designing and implementing effective clinical and public health interventions that lead to sustained dietary changes among individuals and more broadly in the general population.

Definition and classification of hypertension: an update

Since the publication of a paper by the American Society of Hypertension, Inc. Writing Group in 2003, some refinements have occurred in the definition of hypertension. Blood pressure is now recognized as a biomarker for hypertension, and a distinction is made between the various stages of hypertension and global cardiovascular risk. This paper discusses the logic underlying the refinements in the definition of hypertension.

ASH Position Paper: Dietary approaches to lower blood pressure

A substantial body of evidence has implicated several aspects of diet in the pathogenesis of elevated blood pressure (BP). Well-established risk factors for elevated BP include excess salt intake, low potassium intake, excess weight, high alcohol consumption, and suboptimal dietary pattern. African Americans are especially sensitive to the BP-raising effects of excess salt intake, insufficient potassium intake, and suboptimal diet. In this setting, dietary changes have the potential to substantially reduce racial disparities in BP and its consequences. In view of the age-related rise in BP in both children and adults, the direct, progressive relationship of BP with cardiovascular-renal diseases throughout the usual range of BP, and the worldwide epidemic of BP-related disease, efforts to reduce BP in nonhypertensive as well as hypertensive individuals are warranted. In nonhypertensives, dietary changes can lower BP and delay, if not prevent, hypertension. In uncomplicated stage I hypertension, dietary changes serve as initial treatment before drug therapy. In hypertensive individuals already on drug therapy, lifestyle modifications can further lower BP. The current challenge is designing and implementing effective clinical and public health interventions that lead to sustained dietary changes among individuals and more broadly in the general population.

Combination therapy with renin-angiotensin system blockers: Will amlodipine replace hydrochlorothiazide?

Amlodipine is a highly effective and safe antihypertensive dihydropyridine calcium channel blocker. It is even more effective when used in combination with other antihypertensive medications, including hydrochlorothiazide. When antihypertensive calcium channel blockers were first introduced, evidence in the laboratory that they had some natriuretic properties was adduced to suggest that they would be "the diuretics of the 1990s." This turned out not to be the case. Because of its clinical efficacy, amlodipine is frequently used in fixed-dose combination products, but it is not likely to replace hydrochlorothiazide.

David Ayman, MD: An Early Investigator of Clinical Hypertension

Dr. David Ayman (1901-1986) was an astute clinician and observer who challenged medical dogma by performing placebo-controlled studies and by meticulous measurement of blood pressure under standardized conditions. He demonstrated that almost all drugs reported to have an antihypertensive effect in the early 20th century had achieved nothing more than placebo response. He noted the marked variability of blood pressure and devised methods to reduce that variability. These observations led to his publications concerning what is now known as "white coat" or office hypertension. He determined blood pressure personally in 1524 members of 277 families over three generations and made observations on the hereditary nature of hypertension that countered the single-gene thinking of the day. His work is proof that clinical inquisitiveness, hard work, and the courage to challenge conventional wisdom can result in significant contributions to medicine and science.

Variability in response to antihypertensive drugs

Heterogeneity of treatment effects (HTE) is a measure of the variations in individual treatment response to the same agent across a population. Hypertension affords an appropriate model for investigators of HTE. Use of blood pressure measurement guidelines and consistent techniques help to reduce the potential variability associated with clinician measurements. Patient characteristics such as age and race/ethnicity can affect blood pressure, including patient response and adverse events observed with antihypertensive medication. Through pharmacogenetic advances, potential underlying causes for such variation are emerging. The growing number of clinical examples of mutations that affect antihypertensive response includes multiple polymorphisms within the components of the renin-angiotensin-aldosterone system. The most prominent examples of these polymorphisms exist in the genes coding for angiotensinogen, angiotensin-converting enzyme, and the angiotensin II type 1 receptor. An understanding of the components of blood pressure variability and sources of HTE in antihypertensive therapy is important for analyzing published reports on this topic. It is also helpful when designing treatment protocols for individual patients with hypertension and in assessing their response to therapy.

The use of metoprolol CR/XL in the treatment of patients with diabetes and chronic heart failure

About 5 million Americans suffer from heart failure. Given the correlation of heart failure with age and the rising life expectancy, the prevalence of heart failure continues to increase in the general population. Sympathetic stimulation intensifies with progressive heart failure. The rationale to use β-blockers in individuals with impaired myocardial function is based on experimental evidence supporting the notion that prolonged α- and β-adrenergic stimulation leads to worsening heart failure. Until recently, safety concerns have precluded the use of β-blockers in patients with diabetes and heart failure. However, several large, randomized, placebo-controlled clinical trials such as Metoprolol Randomized Intervention Trial in Congestive Heart Failure (MERIT-HF) have shown that β-blockers can be safely used in patients with diabetes and heart failure. Moreover, β-blockers significantly improved morbidity and mortality in this population. Based on this evidence, it is now recommended to add β-blockers such as metoprolol CR/XL with an escalating dosage regimen to the treatment of patients with symptomatic heart failure who already are receiving a stable medical regimen including angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, diuretics, vasodilators, or digitalis.

Nonpharmacologic therapy for hypertension: Does it really work?

Nondrug therapy of hypertension really does work but requires strong motivation by both patient and physician. In addition to global health benefits, prescription of weight loss, exercise, moderation of salt and alcohol intake, Dietary Approach to Stop Hypertension (DASH) eating plan, and tobacco avoidance can decrease the risk for normotensive and prehypertensive patients of developing fixed hypertension. Initiating and maintaining a healthy lifestyle may be sufficient to avoid pharmacologic therapy for some patients and is a valuable adjunct to drug therapy for most. Blood pressure lowering can be achieved by weight reduction (5-20 mm Hg/10 kg), DASH eating plan (8-14 mm Hg), dietary sodium reduction (2-8 mm Hg), increased physical activity (4-9 mm Hg), and moderation of alcohol consumption (2-4 mm Hg). Combination of two or more modalities may have an additive benefit. Cessation of tobacco abuse not only has global health benefits, but may reduce blood pressure.

Treating stage 2 hypertension

The prevalence of hypertension increases with advancing age, due primarily to increases in systolic blood pressure. Systolic hypertension is the most common form of hypertension in individuals over 50 years of age and reflects pathologic decreases in arterial compliance. Systolic blood pressure elevation is a more important risk factor for cardiovascular disease than is diastolic blood pressure elevation. Stage 2 hypertension, defined as blood pressure > or =160/100 mm Hg, is often found in older persons, who are at highest risk for cardiovascular events. In this clinical review, hypertension experts utilize a case study to provide a paradigm for treating older patients with stage 2 hypertension.

Seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure

The National High Blood Pressure Education Program presents the complete Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Like its predecessors, the purpose is to provide an evidence-based approach to the prevention and management of hypertension. The key messages of this report are these: in those older than age 50, systolic blood pressure (BP) of greater than 140 mm Hg is a more important cardiovascular disease (CVD) risk factor than diastolic BP; beginning at 115/75 mm Hg, CVD risk doubles for each increment of 20/10 mm Hg; those who are normotensive at 55 years of age will have a 90% lifetime risk of developing hypertension; prehypertensive individuals (systolic BP 120-139 mm Hg or diastolic BP 80-89 mm Hg) require health-promoting lifestyle modifications to prevent the progressive rise in blood pressure and CVD; for uncomplicated hypertension, thiazide diuretic should be used in drug treatment for most, either alone or combined with drugs from other classes; this report delineates specific high-risk conditions that are compelling indications for the use of other antihypertensive drug classes (angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, beta-blockers, calcium channel blockers); two or more antihypertensive medications will be required to achieve goal BP (<140/90 mm Hg, or <130/80 mm Hg) for patients with diabetes and chronic kidney disease; for patients whose BP is more than 20 mm Hg above the systolic BP goal or more than 10 mm Hg above the diastolic BP goal, initiation of therapy using two agents, one of which usually will be a thiazide diuretic, should be considered; regardless of therapy or care, hypertension will be controlled only if patients are motivated to stay on their treatment plan. Positive experiences, trust in the clinician, and empathy improve patient motivation and satisfaction. This report serves as a guide, and the committee continues to recognize that the responsible physician's judgment remains paramount.

The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: the JNC 7 report

"The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure" provides a new guideline for hypertension prevention and management. The following are the key messages(1) In persons older than 50 years, systolic blood pressure (BP) of more than 140 mm Hg is a much more important cardiovascular disease (CVD) risk factor than diastolic BP; (2) The risk of CVD, beginning at 115/75 mm Hg, doubles with each increment of 20/10 mm Hg; individuals who are normotensive at 55 years of age have a 90% lifetime risk for developing hypertension; (3) Individuals with a systolic BP of 120 to 139 mm Hg or a diastolic BP of 80 to 89 mm Hg should be considered as prehypertensive and require health-promoting lifestyle modifications to prevent CVD; (4) Thiazide-type diuretics should be used in drug treatment for most patients with uncomplicated hypertension, either alone or combined with drugs from other classes. Certain high-risk conditions are compelling indications for the initial use of other antihypertensive drug classes (angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, beta-blockers, calcium channel blockers); (5) Most patients with hypertension will require 2 or more antihypertensive medications to achieve goal BP (<140/90 mm Hg, or <130/80 mm Hg for patients with diabetes or chronic kidney disease); (6) If BP is more than 20/10 mm Hg above goal BP, consideration should be given to initiating therapy with 2 agents, 1 of which usually should be a thiazide-type diuretic; and (7) The most effective therapy prescribed by the most careful clinician will control hypertension only if patients are motivated. Motivation improves when patients have positive experiences with and trust in the clinician. Empathy builds trust and is a potent motivator. Finally, in presenting these guidelines, the committee recognizes that the responsible physician's judgment remains paramount.

Response to six classes of antihypertensive medications by body mass index in a randomized controlled trial

Blood pressure increases with increasing body mass index (BMI) and BMI is linearly related to blood pressure in population studies. Obesity has been said to cause resistance to antihypertensive medications. We compared short-term and 1-year blood pressure response by BMI category and weight change with hydrochlorothiazide, atenolol, diltiazem-SR, captopril, clonidine, prazosin, or placebo in 1292 male veterans. Drug doses were titrated to achieve goal diastolic blood pressure <90 mm Hg over 4-8 weeks. Patients who achieved goal blood pressure were maintained for 1 year. BMI did not predict change in systolic, diastolic or pulse pressures during titration for any drug. At 1 year obese patients (BMI >30) were 2.5 times more likely to have diastolic blood pressure controlled by atenolol than normal weight (BMI <27) patients (p=0.01). Only prazosin patients gained weight: 1.7 lb (end-titration, p<0.0001; 1-year, p=0.02). Obesity does not appear to cause resistance to antihypertensive medications.

Blood pressure-independent impact of antihypertensive agents on cardiovascular and renal disease

Reduction of elevated blood pressure clearly protects against target organ damage, but the different targets do not necessarily benefit to the same degree. There is considerable debate over whether or not there is a drug-specific benefit above and beyond that conferred by blood pressure reduction alone. We performed a Medline search to identify recent randomized clinical trials including 300 or more patients who were followed for at least 2 years. We critically reviewed these papers to find like trials for comparisons. There was too much dissimilarity to perform a meaningful meta-analysis. We found that the literature does not support a definitive conclusion either in favor of or against an overall drug-specific protective effect. However, by grouping like trials, it is possible to support an additional protective effect by angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers on reducing the rate of decline in renal function and in reducing proteinuria.

Effects of severe, uncontrolled hypertension on endothelial activation: soluble vascular cell adhesion molecule-1, soluble intercellular adhesion molecule-1 and von Willebrand factor

OBJECTIVES

The molecular mechanisms whereby severe, uncontrolled hypertension (SHT) is translated into acute vascular target organ dysfunction have not been completely defined. We sought to determine whether SHT is associated with pressure-dependent endothelial activation as assessed by soluble vascular cell adhesion molecule-1 (sVCAM-1), soluble intercellular adhesion molecule-1 (sICAM-1) and von Willebrand Factor (vWF).

METHODS

We determined sVCAM-1, sICAM-1 and vWF in three groups: (i) untreated patients referred specifically for treatment of SHT [diastolic blood pressure (DBP) > or = 120 mm Hg; n = 24]; (ii) untreated patients with established mild hypertension (MHT; DBP 95-100 mmHg; n = 19); and (iii) normotensive volunteers (DBP < or = 90; n = 16).

RESULTS

By analysis of variance, sVCAM-1 (P = 0.002), sICAM-1 (P = 0.02) and vWF (P = 0.009) were greater in SHT and MHT than in normotensives but did not differ between SHT and MHT. We observed a significant positive correlation between blood pressure and soluble activation markers at lower blood pressures (normotensives and MHT considered together) that was not present in SHT.

CONCLUSIONS

Even mild elevation of blood pressure may be sufficient to activate the expression of adhesion molecules. Mechanisms other than the endothelial expression of adhesion molecules may be important in mediating the accelerated target organ injury produced by SHT in humans. Concentrations of soluble adhesion molecules and vWF may depend more strongly upon factors in the hypertensive microenvironment other than the absolute level of blood pressure.