Sodium intake alters the effects of norepinephrine on blood pressure

Sodium - a systematic review for Nordic Nutrition Recommendations 2023

Blood pressure (BP) rises along with increasing sodium intake from early childhood to late adulthood, and leads to hypertension among most men and women living in Nordic and Baltic countries. Elevated BP is the leading global risk factor for premature deaths and disability-adjusted life-years. A reduction in sodium intake is essential in the prevention of hypertension in individuals, in the lowering of BP levels, in the treatment of hypertensive individuals, and in decreasing risks associated with elevated BP. There is a progressive linear dose-response relationship between sodium intake and BP beginning from a sodium intake of less than 0.8 g/day. Sodium reduction decreases BP linearly by a dose-response manner down to a sodium intake level of less than 2 g/day. Randomised intervention studies with a duration of at least 4 weeks confirm the efficiency and safety of reducing blood sodium intake to a level of less than 2 g/day. Results from prospective cohort studies show that higher sodium intake is positively associated with an increased risk of stroke and cardiovascular events and mortality among the general adult population, and the associations are linear in studies using proper sodium assessment methods. Analyses assessing sodium intake using at least two 24-h urine samples have shown a linear positive relationship between sodium intake and the risk of a cardiovascular event or death. Based on an overall evaluation of the available data, a limitation of the sodium intake to 2.0 g/day is suggested for adults. The optimal sodium intake level would be probably about 1.5 g/day. Sodium intake recommended for children can be extrapolated from the recommended sodium intake for adults. According to national dietary surveys, the average sodium intakes in Nordic countries range in adult men from 3.6 to 4.4 g/day and in adult women from 2.6. to 3.2 g/day, and in Baltic countries in men from 2.6 to 5.1 g/day and in women from 1.8 to 3.6 g/day.

Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride

BACKGROUND

Recent cohort studies show that salt intake below 6 g is associated with increased mortality. These findings have not changed public recommendations to lower salt intake below 6 g, which are based on assumed blood pressure (BP) effects and no side-effects.

OBJECTIVES

To assess the effects of sodium reduction on BP, and on potential side-effects (hormones and lipids) SEARCH METHODS: The Cochrane Hypertension Information Specialist searched the following databases for randomized controlled trials up to April 2018 and a top-up search in March 2020: the Cochrane Hypertension Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (from 1946), Embase (from 1974), the World Health Organization International Clinical Trials Registry Platform, and ClinicalTrials.gov. We also contacted authors of relevant papers regarding further published and unpublished work. The searches had no language restrictions. The top-up search articles are recorded under "awaiting assessment."

SELECTION CRITERIA

Studies randomizing persons to low-sodium and high-sodium diets were included if they evaluated at least one of the outcome parameters (BP, renin, aldosterone, noradrenalin, adrenalin, cholesterol, high-density lipoprotein, low-density lipoprotein and triglyceride,.

DATA COLLECTION AND ANALYSIS

Two review authors independently collected data, which were analysed with Review Manager 5.3. Certainty of evidence was assessed using GRADE.

MAIN RESULTS

Since the first review in 2003 the number of included references has increased from 96 to 195 (174 were in white participants). As a previous study found different BP outcomes in black and white study populations, we stratified the BP outcomes by race. The effect of sodium reduction (from 203 to 65 mmol/day) on BP in white participants was as follows: Normal blood pressure: SBP: mean difference (MD) -1.14 mmHg (95% confidence interval (CI): -1.65 to -0.63), 5982 participants, 95 trials; DBP: MD + 0.01 mmHg (95% CI: -0.37 to 0.39), 6276 participants, 96 trials. Hypertension: SBP: MD -5.71 mmHg (95% CI: -6.67 to -4.74), 3998 participants,88 trials; DBP: MD -2.87 mmHg (95% CI: -3.41 to -2.32), 4032 participants, 89 trials (all high-quality evidence). The largest bias contrast across studies was recorded for the detection bias element. A comparison of detection bias low-risk studies versus high/unclear risk studies showed no differences. The effect of sodium reduction (from 195 to 66 mmol/day) on BP in black participants was as follows: Normal blood pressure: SBP: mean difference (MD) -4.02 mmHg (95% CI:-7.37 to -0.68); DBP: MD -2.01 mmHg (95% CI:-4.37, 0.35), 253 participants, 7 trials. Hypertension: SBP: MD -6.64 mmHg (95% CI:-9.00, -4.27); DBP: MD -2.91 mmHg (95% CI:-4.52, -1.30), 398 participants, 8 trials (low-quality evidence). The effect of sodium reduction (from 217 to 103 mmol/day) on BP in Asian participants was as follows: Normal blood pressure: SBP: mean difference (MD) -1.50 mmHg (95% CI: -3.09, 0.10); DBP: MD -1.06 mmHg (95% CI:-2.53 to 0.41), 950 participants, 5 trials. Hypertension: SBP: MD -7.75 mmHg (95% CI:-11.44, -4.07); DBP: MD -2.68 mmHg (95% CI: -4.21 to -1.15), 254 participants, 8 trials (moderate-low-quality evidence).   During sodium reduction renin increased 1.56 ng/mL/hour (95%CI:1.39, 1.73) in 2904 participants (82 trials); aldosterone increased 104 pg/mL (95%CI:88.4,119.7) in 2506 participants (66 trials); noradrenalin increased 62.3 pg/mL: (95%CI: 41.9, 82.8) in 878 participants (35 trials); adrenalin increased 7.55 pg/mL (95%CI: 0.85, 14.26) in 331 participants (15 trials); cholesterol increased 5.19 mg/dL (95%CI:2.1, 8.3) in 917 participants (27 trials); triglyceride increased 7.10 mg/dL (95%CI: 3.1,11.1) in 712 participants (20 trials); LDL tended to increase 2.46 mg/dl (95%CI: -1, 5.9) in 696 participants (18 trials); HDL was unchanged -0.3 mg/dl (95%CI: -1.66,1.05) in 738 participants (20 trials) (All high-quality evidence except the evidence for adrenalin).

AUTHORS' CONCLUSIONS

In white participants, sodium reduction in accordance with the public recommendations resulted in mean arterial pressure (MAP) decrease of about 0.4 mmHg in participants with normal blood pressure and a MAP decrease of about 4 mmHg in participants with hypertension. Weak evidence indicated that these effects may be a little greater in black and Asian participants. The effects of sodium reduction on potential side effects (hormones and lipids) were more consistent than the effect on BP, especially in people with normal BP.

Tolerance to Sodium in Patients With CKD-Induced Metabolic Acidosis: Does the Accompanying Anion Matter?

Patients with chronic kidney disease (CKD) continue to produce endogenous acids but have a reduction in net acid excretion, resulting in a primary decrease in serum bicarbonate concentration, which is termed chronic metabolic acidosis. Recent prospective studies, along with retrospective cohort analyses, demonstrate a higher risk for CKD progression with untreated metabolic acidosis. To normalize serum bicarbonate levels, acidemic patients are often treated with sodium bicarbonate (NaHCO₃) or sodium citrate, which have been shown to slow the progression of CKD. However, studies using this approach have routinely excluded patients with common sodium-sensitive comorbid conditions, such as poorly controlled hypertension, congestive heart failure, volume overload, or edema. This article examines the effect of the anion that accompanies sodium delivered with these therapies. Do the negative effects on blood pressure (BP) and sodium retention, as measured by an increase in edema, weight gain, and congestive heart failure, observed with oral administration of sodium chloride (NaCl) differ when a similar amount of sodium is given with bicarbonate or citrate in this patient population? A review of the literature suggests that NaHCO₃ does not increase BP or sodium retention when administered to patients with CKD during a concurrent severe NaCl dietary restriction (∼10 mEq/d). However, this degree of NaCl restriction is feasible only under strict control in clinical research environments. In contrast, when NaHCO₃ is given to patients without severe dietary NaCl restriction, there is an increase in BP and sodium retention. Thus, unless patients with CKD can tolerate a diet virtually devoid of NaCl, additional sodium, regardless of the accompanying anion, appears to increase BP and sodium retention.

Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride

BACKGROUND

In spite of more than 100 years of investigations the question of whether a reduced sodium intake improves health is still unsolved.

OBJECTIVES

To estimate the effects of low sodium intake versus high sodium intake on systolic and diastolic blood pressure (SBP and DBP), plasma or serum levels of renin, aldosterone, catecholamines, cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglycerides.

SEARCH METHODS

The Cochrane Hypertension Information Specialist searched the following databases for randomized controlled trials up to March 2016: the Cochrane Hypertension Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (2016, Issue 3), MEDLINE (from 1946), Embase (from 1974), the World Health Organization International Clinical Trials Registry Platform, and ClinicalTrials.gov. We also searched the reference lists of relevant articles.

SELECTION CRITERIA

Studies randomising persons to low-sodium and high-sodium diets were included if they evaluated at least one of the above outcome parameters.

DATA COLLECTION AND ANALYSIS

Two review authors independently collected data, which were analysed with Review Manager 5.3.

MAIN RESULTS

A total of 185 studies were included. The average sodium intake was reduced from 201 mmol/day (corresponding to high usual level) to 66 mmol/day (corresponding to the recommended level).The effect of sodium reduction on blood pressure (BP) was as follows: white people with normotension: SBP: mean difference (MD) -1.09 mmHg (95% confidence interval (CI): -1.63 to -0.56; P = 0.0001); 89 studies, 8569 participants; DBP: + 0.03 mmHg (MD 95% CI: -0.37 to 0.43; P = 0.89); 90 studies, 8833 participants. High-quality evidence. Black people with normotension: SBP: MD -4.02 mmHg (95% CI:-7.37 to -0.68; P = 0.002); seven studies, 506 participants; DBP: MD -2.01 mmHg (95% CI:-4.37 to 0.35; P = 0.09); seven studies, 506 participants. Moderate-quality evidence. Asian people with normotension: SBP: MD -0.72 mmHg (95% CI: -3.86 to 2.41; P = 0.65); DBP: MD -1.63 mmHg (95% CI:-3.35 to 0.08; P =0.06); three studies, 393 participants. Moderate-quality evidence.White people with hypertension: SBP: MD -5.51 mmHg (95% CI: -6.45 to -4.57; P < 0.00001); 84 studies, 5925 participants; DBP: MD -2.88 mmHg (95% CI: -3.44 to -2.32; P < 0.00001); 85 studies, 6001 participants. High-quality evidence. Black people with hypertension: SBP MD -6.64 mmHg (95% CI:-9.00 to -4.27; P = 0.00001); eight studies, 619 participants; DBP -2.91 mmHg (95% CI:-4.52, -1.30; P = 0.0004); eight studies, 619 participants. Moderate-quality evidence. Asian people with hypertension: SBP: MD -7.75 mmHg (95% CI:-11,44 to -4.07; P < 0.0001) nine studies, 501 participants; DBP: MD -2.68 mmHg (95% CI: -4.21 to -1.15; P = 0.0006). Moderate-quality evidence.In plasma or serum, there was a significant increase in renin (P < 0.00001), aldosterone (P < 0.00001), noradrenaline (P < 0.00001), adrenaline (P < 0.03), cholesterol (P < 0.0005) and triglyceride (P < 0.0006) with low sodium intake as compared with high sodium intake. All effects were stable in 125 study populations with a sodium intake below 250 mmol/day and a sodium reduction intervention of at least one week.

AUTHORS' CONCLUSIONS

Sodium reduction from an average high usual sodium intake level (201 mmol/day) to an average level of 66 mmol/day, which is below the recommended upper level of 100 mmol/day (5.8 g salt), resulted in a decrease in SBP/DBP of 1/0 mmHg in white participants with normotension and a decrease in SBP/DBP of 5.5/2.9 mmHg in white participants with hypertension. A few studies showed that these effects in black and Asian populations were greater. The effects on hormones and lipids were similar in people with normotension and hypertension. Renin increased 1.60 ng/mL/hour (55%); aldosterone increased 97.81 pg/mL (127%); adrenalin increased 7.55 pg/mL (14%); noradrenalin increased 63.56 pg/mL: (27%); cholesterol increased 5.59 mg/dL (2.9%); triglyceride increased 7.04 mg/dL (6.3%).

Association between pre hemodialysis serum sodium concentration and blood pressure: results from a retrospective analysis from the international monitoring dialysis outcomes (MONDO) initiative

A recent study from the United Kingdom indicates an association between pre hemodialysis (HD) serum sodium (SNa(+)) and systolic and diastolic blood pressure (SBP and DBP) in chronic HD patients. We extend this analysis to an international cohort of incident HD patients. The Monitoring Dialysis Outcomes initiative encompasses patients from 41 countries. Over 2 years monthly pre-HD SNa(+) levels were used as predictors of pre-HD SBP and DBP in a linear mixed model (LMM) adjusted for age, gender, interdialytic weight gain, diabetes, serum albumin and calcium. Similar models were constructed with DBP as outcome. Analyses were carried out stratified by continent (North and South America; Europe and Asia). LMMs were also constructed for the entire observation period of 2 years, and separately the first and the second year after HD initiation. We studied 17 050 incident patients and found SNa(+) to have a significant slope estimate in the LMM predicting pre-HD SBP and DBP (ranging from 0.22 to 0.29 and 0.10 to 0.21 mm Hg per mEq l(-1), respectively, between the continents). The findings were similar in subsets of SBP and SNa(+) tertiles, and separately analyzed for the first and second year. Our analysis shows an independent association between SNa, SBP and DBP in a large intercontinental database, indicating that this relation is a profound biological phenomenon in incident and prevalent HD patients, generalizable to an international level and independent of SBP and DBP magnitude.

The hidden hand of chloride in hypertension

Among the environmental factors that affect blood pressure, dietary sodium chloride has been studied the most, and there is general consensus that increased sodium chloride intake increases blood pressure. There is accruing evidence that chloride may have a role in blood pressure regulation which may perhaps be even more important than that of Na⁺. Though more than 85 % of Na⁺ is consumed as sodium chloride, there is evidence that Na⁺ and Cl⁻ concentrations do not go necessarily hand in hand since they may originate from different sources. Hence, elucidating the role of Cl⁻ as an independent player in blood pressure regulation will have clinical and public health implications in addition to advancing our understanding of electrolyte-mediated blood pressure regulation. In this review, we describe the evidence that support an independent role for Cl⁻ on hypertension and cardiovascular health.

Effects of low-sodium diet vs. high-sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride (Cochrane Review)

BACKGROUND

The question of whether reduced sodium intake is effective as a health prophylaxis initiative is unsolved. The purpose was to estimate the effects of low-sodium vs. high-sodium intake on blood pressure (BP), renin, aldosterone, catecholamines, and lipids.

METHODS

Studies randomizing persons to low-sodium and high-sodium diets evaluating at least one of the above outcome parameters were included. Data were analyzed with Review Manager 5.1.

RESULTS

A total of 167 studies were included. The effect of sodium reduction in: (i) Normotensives: Caucasians: systolic BP (SBP) -1.27 mm Hg (95% confidence interval (CI): -1.88, -0.66; P = 0.0001), diastolic BP (DBP) -0.05 mm Hg (95% CI: -0.51, 0.42; P = 0.85). Blacks: SBP -4.02 mm Hg (95% CI: -7.37, -0.68; P = 0.002), DBP -2.01 mm Hg (95% CI: -4.37, 0.35; P = 0.09). Asians: SBP -1.27 mm Hg (95% CI: -3.07, 0.54; P = 0.17), DBP -1.68 mm Hg (95% CI: -3.29, -0.06; P = 0.04). (ii) Hypertensives: Caucasians: SBP -5.48 mm Hg (95% CI: -6.53, -4.43; P < 0.00001), DBP -2.75 mm Hg (95% CI: -3.34, -2.17; P < 0.00001). Blacks: SBP -6.44 mm Hg (95% CI: -8.85, -4.03; P = 0.00001), DBP -2.40 mm Hg (95% CI: -4.68, -0.12; P = 0.04). Asians: SBP -10.21 mm Hg (95% CI: -16.98, -3.44; P = 0.003), DBP -2.60 mm Hg (95% CI: -4.03, -1.16; P = 0.0004). Sodium reduction resulted in significant increases in renin (P < 0.00001), aldosterone (P < 0.00001), noradrenaline (P < 0.00001), adrenaline (P < 0.0002), cholesterol (P < 0.001), and triglyceride (P < 0.0008).

CONCLUSIONS

Sodium reduction resulted in a significant decrease in BP of 1% (normotensives), 3.5% (hypertensives), and a significant increase in plasma renin, plasma aldosterone, plasma adrenaline, and plasma noradrenaline, a 2.5% increase in cholesterol, and a 7% increase in triglyceride.

Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride

BACKGROUND

In spite of more than 100 years of investigations the question of reduced sodium intake as a health prophylaxis initiative is still unsolved.

OBJECTIVES

To estimate the effects of low sodium versus high sodium intake on systolic and diastolic blood pressure (SBP and DBP), plasma or serum levels of renin, aldosterone, catecholamines, cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglycerides.

SEARCH METHODS

PUBMED, EMBASE and Cochrane Central and reference lists of relevant articles were searched from 1950 to July 2011.

SELECTION CRITERIA

Studies randomizing persons to low sodium and high sodium diets were included if they evaluated at least one of the above outcome parameters.

DATA COLLECTION AND ANALYSIS

Two authors independently collected data, which were analysed with Review Manager 5.1.

MAIN RESULTS

A total of 167 studies were included in this 2011 update.The effect of sodium reduction in normotensive Caucasians was SBP -1.27 mmHg (95% CI: -1.88, -0.66; p=0.0001), DBP -0.05 mmHg (95% CI: -0.51, 0.42; p=0.85). The effect of sodium reduction in normotensive Blacks was SBP -4.02 mmHg (95% CI:-7.37, -0.68; p=0.002), DBP -2.01 mmHg (95% CI:-4.37, 0.35; p=0.09). The effect of sodium reduction in normotensive Asians was SBP -1.27 mmHg (95% CI: -3.07, 0.54; p=0.17), DBP -1.68 mmHg (95% CI:-3.29, -0.06; p=0.04). The effect of sodium reduction in hypertensive Caucasians was SBP -5.48 mmHg (95% CI: -6.53, -4.43; p<0.00001), DBP -2.75 mmHg (95% CI: -3.34, -2.17; p<0.00001). The effect of sodium reduction in hypertensive Blacks was SBP -6.44 mmHg (95% CI:-8.85, -4.03; p=0.00001), DBP -2.40 mmHg (95% CI:-4.68, -0.12; p=0.04). The effect of sodium reduction in hypertensive Asians was SBP -10.21 mmHg (95% CI:-16.98, -3.44; p=0.003), DBP -2.60 mmHg (95% CI: -4.03, -1.16; p=0.0004).In plasma or serum there was a significant increase in renin (p<0.00001), aldosterone (p<0.00001), noradrenaline (p<0.00001), adrenaline (p<0.0002), cholesterol (p<0.001) and triglyceride (p<0.0008) with low sodium intake as compared with high sodium intake. In general the results were similar in studies with a duration of at least 2 weeks.

AUTHORS' CONCLUSIONS

Sodium reduction resulted in a 1% decrease in blood pressure in normotensives, a 3.5% decrease in hypertensives, a significant increase in plasma renin, plasma aldosterone, plasma adrenaline and plasma noradrenaline, a 2.5% increase in cholesterol, and a 7% increase in triglyceride. In general, these effects were stable in studies lasting for 2 weeks or more.

Association between blood pressure responses to the cold pressor test and dietary sodium intervention in a Chinese population

BACKGROUND

Blood pressure (BP) responses to the cold pressor test (CPT) and to dietary sodium intake might be related to the risk of hypertension. We examined the association between BP responses to the CPT and to dietary sodium and potassium interventions.

METHODS

The CPT and dietary intervention were conducted among 1906 study participants in rural China. The dietary intervention included three 7-day periods of low sodium intake (3 g/d of salt [sodium chloride] [51.3 mmol/d of sodium]), high sodium intake (18 g/d of salt [307.8 mmol/d of sodium]), and high sodium intake plus potassium chloride supplementation (60 mmol/d). A total of 9 BP measurements were obtained during the 3-day baseline observation and the last 3 days of each intervention using a random-zero sphygmomanometer.

RESULTS

Blood pressure response to the CPT was significantly associated with BP changes during the sodium and potassium interventions (all P < .001). Compared with the lowest quartile of BP response to the CPT (quartile 1), systolic BP changes (95% confidence intervals) for the quartiles 2, 3, and 4 were -2.02 (-2.87 to -1.16) mm Hg, -3.17 (-4.05 to -2.28) mm Hg, and -5.98 (-6.89 to -5.08) mm Hg, respectively, during the low-sodium intervention. Corresponding systolic BP changes during the high-sodium intervention were 0.40 (-0.36 to 1.16) mm Hg, 0.44 (-0.35 to 1.22) mm Hg, and 2.30 (1.50 to 3.10) mm Hg, respectively, and during the high-sodium plus potassium supplementation intervention were -0.26 (-0.99 to 0.46) mm Hg, -0.95 (-1.70 to -0.20) mm Hg, and -1.59 (-2.36 to -0.83) mm Hg, respectively.

CONCLUSIONS

These results indicate that BP response to the CPT was associated with salt sensitivity and potassium sensitivity. Furthermore, a low-sodium or high-potassium diet might be more effective to lower BP among individuals with high responses to the CPT.

Effects of dietary sodium chloride intake on renal function and blood pressure in cats with normal and reduced renal function

OBJECTIVE

To determine effects of variations in dietary intake of sodium chloride (NaCl) on systemic arterial blood pressure (ABP) in cats with normal and reduced renal function.

ANIMALS

21 adult cats (7 with intact kidneys [control cats; group C], 7 with unilateral renal infarction with contralateral nephrectomy [remnant-kidney model; group RK], and 7 with unilateral renal infarction and contralateral renal wrapping and concurrent oral administration of amlodipine [remnant-wrap model; group WA]).

PROCEDURE

All cats were sequentially fed 3 diets that differed only in NaCl content (50, 100, or 200 mg of Na/kg); each diet was fed for 7 days. The ABP was recorded continuously by radiotelemetry, and renal function (glomerular filtration rate [GFR]) was determined on the sixth day of each feeding period.

RESULTS

Dietary supplementation with NaCl did not affect ABP, but it increased GFR in groups C and WA. The renin-angiotensin-aldosterone axis was activated in groups RK and WA at the lowest NaCl intake, but supplementation with NaCl suppressed this activation in group WA. The lowest NaCl intake was associated with hypokalemia and a high fractional excretion of potassium that decreased in response to supplementation with NaCl. Arterial baroreceptor resetting was evident after chronic hypertension but was not modified by dietary supplementation with NaCl.

CONCLUSIONS AND CLINICAL RELEVANCE

Low NaCl intake was associated with inappropriate kaliuresis, reduced GFR, and activation of the renin-angiotensin-aldosterone axis without evidence of a beneficial effect on ABP. Therefore, this common dietary maneuver could contribute to hypokalemic nephropathy and progressive renal injury in cats.

Norepinephrine kinetics in dogs with experimentally induced renal vascular hypertension

OBJECTIVE

To determine norepinephrine (NE) kinetics in dogs with experimentally induced renal vascular hypertension.

ANIMALS

4 mixed-breed dogs.

PROCEDURE

The study comprised a control and hypertensive period. The hypertensive period followed induction of renal vascular hypertension achieved by surgical placement of clips on both renal arteries to reduce diameter by approximately 80%. Arterial blood pressure, renal clearance, and NE kinetics were measured during each period while dogs were receiving a low-sodium diet. Measurements of NE kinetics and renal clearance during the hypertensive period were made 5 days after induction of hypertension.

RESULTS

Five days after induction of hypertension, arterial blood pressure increased by 15 to 20 mm Hg. Mean (+/- SEM) plasma NE concentration and NE spillover rate increased significantly from 151.5+/-14.1 pg/ml and 8.03+/-0.62 ng/kg/min, respectively, during the control period to 631.4+/-30.5 pg/ml and 54.0+/-5.2 ng/kg/min, respectively, during the hypertensive period. Norepinephrine clearance rate also increased (54.0+/-2.4 vs. 86.0+/-9.3 ml/kg/min). Positive associations between mean arterial pressure (MAP) and NE concentration and spillover rate were detected. However, MAP and NE clearance rate were not associated.

CONCLUSIONS AND CLINICAL RELEVANCE

Increased blood pressure during the hypertensive period was likely attributable to increased NE spillover rate, which resulted in a significant increase in plasma NE concentration. Analysis of these results suggests that central sympathetic outflow was increased and may be responsible for the pathogenesis of high blood pressure during the acute phase of renal vascular hypertension in dogs.

Sodium-sensitive hypertension is not associated with higher sympathetic nervous system activity in older hypertensive humans

The majority of older hypertensive humans are sodium sensitive and they are characterized by increased alpha-adrenergic responsiveness relative to their level of sympathetic nervous system (SNS) activity. To test the hypothesis that heightened SNS activity and/or increased alpha-adrenergic receptor responsiveness during sodium loading may play a role in the sodium-dependent increase in blood pressure in older sodium-sensitive hypertensives, we used compartmental analysis of [3H]norepinephrine (NE) kinetics to determine the release rate of NE into an extravascular compartment (NE2) as an index of systemic SNS activity and determined forearm blood flow responses to graded intrabrachial artery NE and angiotensin II (ANG II) infusions and platelet membrane alpha2-receptor properties in 24 older (age 64 +/- 7 years) hypertensive subjects. Subjects were studied at the end of 1 week of a low (20 mmol/day)- and again at the end of 1 week of a high (200 mmol/day)-sodium diet. Subjects were categorized as sodium sensitive (SS) if they had a > or = 5 mm Hg increase in mean arterial blood pressure (MABP) with dietary sodium loading (n = 16), or sodium-resistant (SR) if their MABP increased by < 5 mm Hg (n = 8). Neither dietary sodium intake nor sodium-sensitivity status significantly affected arterial plasma NE levels, NE2, or other NE kinetic parameters. Forearm blood flow responses to NE or to ANG II, and platelet alpha2-receptor properties were similar between the SS and SR groups. These results suggest that the sodium-dependent increase in MABP that characterizes SS hypertension among older humans is not because of an increase in systemic SNS activity or increased arterial adrenergic receptor responsiveness.

Role of angiotensin II in regulation of basal and sympathetically stimulated vascular tone in early and advanced cirrhosis

BACKGROUND & AIMS

The renin-angiotensin and sympathetic nervous systems are activated in cirrhosis. This study aimed to establish the role of angiotensin II (ANG II) in the regulation of basal and sympathetically stimulated vascular tone in preascitic cirrhotic patients and patients with diuretic-refractory ascites compared with age- and sex-matched healthy controls.

METHODS

Forearm blood flow (FBF) responses to lower body negative pressure (LBNP) and to subsystemic, intrabrachial infusions of losartan, an angiotensin II type 1 (AT(1)) receptor antagonist, norepinephrine, and ANG II were measured using venous occlusion plethysmography.

RESULTS

In all groups, ANG II and norepinephrine caused dose-dependent reductions in FBF (P < 0.001); responses to norepinephrine were similar across the 3 groups but those to ANG II were less in both cirrhotic groups than in controls (P < 0.01). Losartan caused a dose-dependent increase in FBF only in patients with refractory ascites (P < 0.01). LBNP caused less reduction in FBF in refractory ascites patients than in both preascitic patients and controls (P < 0.01).

CONCLUSIONS

Despite hyporesponsiveness to exogenous ANG II in both early and advanced cirrhosis, endogenous ANG II contributes to the maintenance of basal vascular tone only in advanced cirrhosis. These findings suggest a role of ANG II in the pathogenesis of ascites. Attenuated LBNP responses occurred only in advanced cirrhosis, without apparent interaction with endogenous ANG II.

Increased pressor response to noradrenaline in pituitary dependent Cushing's syndrome

OBJECTIVES

The mechanism of hypertension in Cushing's syndrome remains undetermined. Some studies have demonstrated an increased sensitivity to pressor agents but it is not clear if patients with Cushing's syndrome of different aetiologies demonstrate this finding. We have examined pressor sensitivity in a group of patients with Cushing's disease (pituitary dependent hypercortisolism) by measuring blood pressure during incrementally increasing infusions of noradrenaline.

METHODS

Eight subjects (7 female, 1 male), aged 42.2 +/- 4.5 years (mean +/- SEM) with Cushing's disease were studied. Eight age- and sex-matched control subjects were also studied. Four of the eight controls and five patients with Cushing's disease had elevated blood pressure. All medication for this had been stopped at least seven days prior to the study. After subjects ate a light breakfast, ECG leads and a sphygmomanometer were attached, an intravenous cannula was inserted and all subjects then rested quietly for 60 minutes. Noradrenaline was then infused intravenously for 10-minute periods at concentrations of 0.01, 0.03, 0.07, 0.11 and 0.18 microg/kg/minute.

RESULTS

On the day of the study the baseline blood pressures and pulse rates in the patients with Cushing's disease (blood pressure; 138/87 +/- 6/3 mmHg, pulse 76.5 +/- 4.8 beats/minute) and controls (blood pressure; 126/86 +/- 6/6 mmHg, pulse 71.2 +/- 3.7 beats/minute) were not significantly different. The mean change in diastolic blood pressure from baseline at the time of the peak increase or when the test was stopped was 21. 5 +/- 4.7 mmHg in Cushing's disease compared to 7.0 +/- 2.5 mmHg in controls (P = 0.03). The mean change in mean arterial pressure from baseline at the time of the peak increase or when the test was stopped was 22.0 +/- 4.0 mmHg in Cushing's disease compared to 13.0 +/- 2.4 mmHg in controls (P = 0.03). No significant difference in mean change of systolic pressure (26.0 +/- 4.6 vs. 25 +/- 4.0 mmHg) or pulse rates (- 11.1 +/- 1.8 vs. - 4.7 +/- 2.6) was seen in the group with Cushing's disease as compared to the control group.

CONCLUSIONS

We conclude that patients with pituitary-dependent Cushing's syndrome have enhanced pressor diastolic and mean arterial responses to noradrenaline and this may be an important underlying mechanism for the hypertension seen in this particular group of Cushing's syndrome patients.

Reduced dietary potassium reversibly enhances vasopressor response to stress in African Americans

Acute vasopressor responses to stress are adrenergically mediated and hence potentially subject to differential modulation by dietary potassium and sodium. The greater vasopressor responsiveness in blacks compared with whites might then be consequent not only to a high dietary salt intake but also to a marginally reduced dietary potassium intake. Under controlled metabolic conditions, we compared acute vasopressor responses to cold and mental stress in black and white normotensive men during three successive dietary periods: (1) while dietary potassium was reduced (30 mmol K+/70 kg per day) and salt was restricted (10 to 14 days); (2) while salt was loaded (15 to 250 mmol Na+/70 kg per day) (7 days); and (3) while salt loading was continued and potassium was either supplemented (70 mmol K+/70 kg per day) (7 to 21 days) in 9 blacks and 6 whites or continued reduced (30 mmol K+/70 kg per day) (28 days) in 4 blacks (time controls). At the lower potassium intake, cold-induced increase in forearm vascular resistance in blacks was twice that in whites during both salt restriction and salt loading. Normalization of dietary potassium attenuated cold-induced increases in both forearm vascular resistance and systolic and diastolic blood pressures in blacks but only in systolic pressure in whites. In blacks but not in whites, normalization of dietary potassium attenuated mental stress-induced increases in systolic and diastolic pressures. In normotensive blacks but not whites, a marginally reduced dietary intake of potassium reversibly enhances adrenergically mediated vasopressor responsiveness to stress. That responsiveness so enhanced over time might contribute to the pathogenesis of hypertension in blacks.

Effects of sodium salts on pressor reactivity in salt-sensitive men

Blood pressure in patients with essential hypertension is raised by sodium chloride but not by nonchloride sodium salts. Although a high sodium chloride diet is known to augment the pressor response to norepinephrine and angiotensin II, the effect of nonchloride sodium salts on pressor responsiveness has not been studied so far. To examine whether sodium chloride and nonchloride sodium salts evoke different pressor responses to these agonists, we performed graded norepinephrine and angiotensin II infusions in salt-sensitive (n = 7) and salt-resistant (n = 8) normotensive subjects. The subjects were given a low salt diet (20 mmol/day) for 3 weeks, to which a supplement of 200 mmol sodium per day, provided as either sodium chloride or sodium citrate, or a placebo was added for 1 week each. We found that, although sodium chloride raised mean arterial blood pressure in the salt-sensitive subjects (p less than 0.005), sodium citrate did not. However, under both sodium salts pressor response to norepinephrine and angiotensin II was significantly greater than under placebo (p less than 0.02). Furthermore, with both sodium salts, pressor response in the salt-sensitive subjects was greater than in the salt-resistant subjects (p less than 0.01). This study thus demonstrates that, although blood pressure in salt-sensitive individuals is raised by sodium chloride only, both sodium chloride and sodium citrate evoke similar increases in pressor response to norepinephrine and angiotensin II. Since pressor response increased with both sodium salts but resting blood pressure increased only with sodium chloride, enhanced pressor responsiveness alone cannot account for the sodium chloride-induced rise in resting blood pressure.

Blood pressure hyperreactivity in non-human primates during dietary sodium combined with behavioral stress

The potential for behavioral stress alone or combined with dietary salt to augment pressor reactivity to the onset of daily experimental sessions was examined in normotensive, intact baboons over the course of four months. During twice daily experimental sessions, adult male baboons experienced food/shock conflict such that lever pulling not only served to earn food, but was also occasionally punished with cued mild electric shock. Blood pressure and heart rate were measured during a baseline period of fixed-ratio food reinforcement (3 weeks), during conflict stress (2 weeks), and after dietary salt was added to the daily conflict protocol (CONFLICT + SODIUM, 3 weeks). Reactivity, i.e., acute changes in blood pressure and heart rate to the daily experimental sessions, was not evident during food reinforcement sessions nor during the CONFLICT stress alone condition. The addition of a high salt diet virtually doubled blood pressure increases and heart rate decreases to the onset of experimental sessions. Average reactivities during CONFLICT + SODIUM periods were 11.2/7.9% delta for SBP/DBP (systolic/diastolic blood pressure, mmHg), and -5.65% delta for HR (heart rate, BPM). Neither atenolol nor hydrochlorothiazide diuretic significantly altered cardiovascular reactivity during CONFLICT + SODIUM in comparison to a preceding non-drug CONFLICT + SODIUM period. When atenolol and diuretic effects were directly compared, atenolol mildly augmented, while diuretic mildly decreased DBP but not SBP reactivity during CONFLICT + SODIUM. Reactivity was eliminated after salt loading and behavioral sessions were terminated. These findings provide evidence that enhanced salt ingestion may synergistically act with behavioral stress to produce pressor hyperresponsiveness to otherwise benign environmental events.

Effects of salt, race, and hypertension on reactivity to stressors

Blood pressure and heart rate reactivity to a psychological stressor and to a cold pressor test were examined in a group of 51 normotensive and 37 unmedicated hypertensive men. All were studied twice, once while the participants were maintained on a moderately high salt (200 meq sodium/day) diet and once while the participants were maintained on an extremely low salt (10 meq sodium/day) diet. Dietary salt had no effect on blood pressure or heart rate responses to the two stressors. The systolic and diastolic responses of the white participants to the psychological stressor were greater than those of the black participants (both p less than 0.05); however, there was no difference between blacks and whites in reactivity to the cold pressor challenge. As compared with the normotensive group, the hypertensive group reacted to the psychological stressor with increased responses in systolic blood pressure, diastolic blood pressure, and heart rate (all p less than 0.05). The hypertensive group also hyperresponded in terms of the systolic pressure response to the cold pressor task (p less than 0.05). Plasma norepinephrine and epinephrine responses were not significantly different across the two diets, races, or diagnoses.

Metabolic considerations in the treatment of the black hypertensive

Hypertension and its cardiovascular consequences are both common and potentially devastating among black Americans. Recent evidence suggests that not all antihypertensive agents have similar efficacy in hypertensive patients, nor do all convey the same benefit in terms of reducing the risk of cardiovascular disease. This review considers the efficacy of various antihypertensive agents in blacks, with particular reference to the impact of these agents on cardiovascular disease risk factors and on associated diseases often encountered in black hypertensives. Emphasis is placed on the use of therapeutic approaches other than diuretics alone or in combination with other antihypertensive agents from the vantage point of efficacy and enhancement of cardiovascular and metabolic benefits.

Elevated sympathetic nerve activity in borderline hypertensive humans. Evidence from direct intraneural recordings

Reports of elevated plasma catecholamine levels and augmented responses to autonomic blockade suggest increased sympathetic tone in borderline hypertension. It is not known if this reflects greater sympathetic neural outflow. We directly recorded muscle sympathetic nerve activity (microneurography) in 15 normotensive and 12 borderline hypertensive age-matched men to determine whether borderline hypertensive individuals have elevated sympathetic nerve activity. Supine heart rate, blood pressure, plasma norepinephrine, and efferent muscle sympathetic nerve activity (peroneal nerve) were measured after 6 days of both low and high dietary sodium intake (10 and 400 meq sodium/24 hr). Sympathetic nerve activity was elevated significantly in borderline hypertensive individuals on both low (37 +/- 1 in borderline hypertensive individuals vs. 29 +/- 1 bursts/min in normotensive individuals; p less than 0.01) and high (25 + 1 in borderline hypertensive individuals vs. 16 +/- 1 bursts/min in normotensive individuals; p less than 0.01) sodium diets. The borderline hypertensive group had higher systolic (p less than 0.01) and diastolic (p less than 0.05) blood pressures independent of sodium intake. Across both groups, high sodium intake reduced muscle sympathetic nerve activity (p less than 0.001), plasma norepinephrine (p less than 0.001), diastolic blood pressure (p less than 0.02), heart rate (p less than 0.002), and increased weight (p less than 0.005). A significant (p less than 0.05) group-by-diet interaction was observed for plasma norepinephrine levels. Specifically, compared with the normotensive group, plasma norepinephrine levels in the borderline hypertensive group tended to be higher on low sodium diet (p = 0.08) and lower on high sodium diet (p = 0.23).(ABSTRACT TRUNCATED AT 250 WORDS)

Inverse regulation of alpha-2 and beta-2 adrenoceptors in salt-sensitive hypertension: an hypothesis

A high salt diet leads to up-regulation of alpha-2 adrenoceptors and down-regulation of beta-2 adrenoceptors in normotensive subjects. Although the increase in blood pressure with a high salt diet is not related to the magnitude of the alpha-2 or beta-2 adrenoceptor changes alone, it is related to the increase in the ratio of the receptor changes (operative alpha/beta adrenoceptor ratio). An increase in the operative alpha/beta adrenoceptor ratio with a high salt intake results in vasoconstriction and reduced vasodilatation at resistance vessels, as well as increased renal proximal tubular sodium reabsorption. An influence of heredity on this relationship is supported by four lines of evidence: 1) salt-sensitivity of blood pressure occurs predominantly in subjects with a family history of hypertension; 2) studies in twin children document the influence of genetic variance on salt-sensitivity of blood pressure; 3) subjects with a family history of hypertension have a significantly lower salivary sodium concentration and an altered urinary sodium excretion after salt loading compared to subjects with no such history; 4) salt-sensitivity of blood pressure may be associated with specific genetic markers. On the basis of these observations, we propose the hypothesis that enhanced inverse alpha-beta-adrenoceptor regulation in response to a high salt intake may be responsible for salt sensitivity in the normal population, and may contribute to the development of essential hypertension in susceptible individuals. This alteration is likely to be genetically mediated.

Norepinephrine responsiveness in patients with borderline hypertension under three different sodium balances

The pressor effects of intravenous norepinephrine (NE) infusion (100 and 200 ng/kg/min for 15 min) were examined in 17 patients with borderline hypertension (BHT) and 15 age-matched normotensive subjects (NT) under three different sodium balances; the regular customary diet, treatment with diuretics, and the high-sodium diet. Treatment with diuretics decreased and high sodium diet increased the pressor response to NE in both groups but there were no significant differences in NE reactivity between the groups. The increments in mean blood pressure after NE infusion (200 ng/kg/min) during the three experimental periods correlated significantly with the preinfusion plasma NE concentration in both BHT and NT: r = -0.58 (p less than 0.01) and r = -0.54 (p less than 0.01), respectively. Neither the slopes nor the intercepts differed between the two groups. Thus, evidence presented indicates that BHT do not have increased pressor responsiveness to NE, and that NE pressor response depends upon basal sympathetic tone.

Peripheral arterial vasodilation hypothesis: a proposal for the initiation of renal sodium and water retention in cirrhosis

Renal sodium and water retention and plasma volume expansion have been shown to precede ascites formation in experimental cirrhosis. The classical "underfilling" theory, in which ascites formation causes hypovolemia and initiates secondary renal sodium and water retention, thus seems unlikely. While the occurrence of primary renal sodium and water retention and plasma volume expansion prior to ascites formation favors the "overflow" hypothesis, the stimulation of the renin-angiotensin-aldosterone system, vasopressin release and sympathetic nervous system associated with cirrhosis is not consonant with primary volume expansion. In this present article, the "Peripheral Arterial Vasodilation Hypothesis" is proposed as the initiator of sodium and water retention in cirrhosis. Peripheral arterial vasodilation is one of the earliest observations in the cirrhotic patient and experimental animals with cirrhosis. Arterial vasodilators and arteriovenous fistula are other examples in which renal sodium and water retention occur secondary to a decreased filling of the arterial vascular tree. An increase in cardiac output and hormonal stimulation are common features of cirrhosis, arteriovenous fistula and drug-induced peripheral arterial vasodilation. However, a predilection for the retained sodium and water to transudate into the abdominal cavity occurs with cirrhosis because of the presence of portal hypertension. The Peripheral Arterial Vasodilation Hypothesis also explains the continuum from compensated to decompensated cirrhosis to the hepatorenal syndrome.

Age, race, diagnosis, and sodium effects on the pressor response to infused norepinephrine

We studied the blood pressure responses to infused norepinephrine in 34 normotensive and 21 unmedicated subjects with essential hypertension. The two groups were similar in age, relative body weight, and urinary electrolyte excretion. Patients were studied on two extremes of dietary salt (200 mEq Na and 10 mEq Na per day). The dose-response curves were highly linear (p less than 0.00001) for both systolic and diastolic blood pressures. There was no evidence for an increased sensitivity to infused norepinephrine among the hypertensive subjects. On the other hand, older subjects had steeper slopes (p less than 0.005). Subjects on a high salt diet had steeper slopes than those on low salt diets (p less than 0.0025); this trend was especially apparent among blacks (p less than 0.005). Black and white hypertensive subjects responded to the high salt diet in opposite fashion: The blacks showed an increased pressor sensitivity (p less than 0.05), whereas the whites demonstrated a nonsignificant decreased pressor sensitivity. These results indicate that age, race, and salt effects must be meticulously controlled in studies of sympathetic nervous system physiology.

Adrenergic receptors and sodium reabsorption in normotensive subjects as related to salt sensitivity

We have studied proximal tubular sodium reabsorption as measured by lithium clearance, alpha-2 and beta-2 adrenergic receptors on circulating platelets and lymphocytes, respectively, and urinary aldosterone after variations of sodium intake in 24 normotensive volunteers. Fractional lithium clearance was 14.8% +/- 2.64 under a high salt diet of 200 mmol per day. After a low salt diet of 50 mmol/d for two weeks fractional lithium clearance did not change significantly (13.3% +/- 3.35). There were no correlations between alpha-2 adrenergic receptors, beta-2 adrenergic receptors or the alpha-2/beta-2 ratio and fractional lithium clearance, irrespective of the high or low salt diet. In contrast, a significant correlation was found between urinary aldosterone excretion and alpha-2 receptor densities under low salt diet (r = -0.55, n = 17, p less than 0.02). There were no correlations between beta-2 adrenoceptor density, alpha-2/beta-2 ratio and urinary aldosterone during high or low salt diet. Whereas our results are inconclusive about the value of lithium clearance determinations as a measure of proximal tubular sodium reabsorption during variations of sodium intake, we conclude, that alpha-adrenoceptor density, as measured on circulating blood cells, may possibly be representative for alpha-adrenergic equipment of the kidney. The inverse correlation between urinary aldosterone excretion in subjects equilibrated on a low salt diet of 50 mmol/d and alpha-2 adrenoceptor densities could be interpreted as an indirect evidence, that those subjects with a high alpha-2 adrenoceptor equipment show a high proximal tubular sodium reabsorption and thus can afford a low rate of aldosterone mediated distal tubular sodium reabsorption to maintain sodium balance. Our results are thus in accord with our previous hypothesis, that different receptor equipment of individual subjects may cause marked differences in sodium handling by the kidney. These differences may be responsible, at least in part, for the degree of salt sensitivity in individual subjects.

Definitions and characteristics of sodium sensitivity and blood pressure resistance

Sensitivity and resistance to the effects of sodium were evaluated in normotensive and hypertensive humans by two approaches. Blood pressure was measured after an intravenous infusion of 2 L of normal (0.9%) saline and after sodium and volume depletion induced by a low sodium diet and furosemide administration in 378 normal volunteers and 198 subjects with essential hypertension. Those in whom mean arterial blood pressure decreased by at least 10 mm Hg after sodium and volume depletion were considered sodium-sensitive, and those with a decrease of 5 mm Hg or less (including an increase in pressure) were considered sodium-resistant. The second study utilized the blood pressure response to modest dietary sodium restriction in 74 normotensive subjects to identify sodium sensitivity and resistance. In both studies the responses were heterogeneous. In the first study significantly more hypertensive subjects were sodium-sensitive, as compared with those in the normotensive group (p less than 0.001). Plasma renin activity (low, normal, or high) did not predict sodium responses. In both groups sodium-sensitive individuals were significantly older (p less than 0.001) and had lower baseline renin values than sodium-resistant subjects. Factors related to the change in mean arterial blood pressure after sodium and volume depletion included baseline pressure (r = -0.54, p less than 0.001) and age (r = -0.16, p = 0.002 in the normotensive group; r = -0.28, p less than 0.001 in the hypertensive group). The response to dietary sodium restriction was also correlated with baseline pressure (r = 0.61, p less than 0.001) and the initial urinary sodium excretion (r = 0.27, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood pressure control in normotensive members of hypertensive families

The cardiovascular pressor responses to a stepwise increase in plasma norepinephrine or angiotensin II concentrations, induced by infusions, were studied in 23 normotensive subjects with a negative and 25 with a positive family history of essential hypertension. The two study groups had a similar mean age (24 +/- 2 (SD) yr), body weight, blood pressure (112/64 +/- 10/7 mmHg), heart rate, plasma and urinary sodium and potassium, and plasma norepinephrine, epinephrine, angiotensin II, renin and aldosterone levels. However, subjects with positive history differed from those with negative history of hypertension by a decreased pressor dose of infused norepinephrine (89 +/- 29 vs. 135 +/- 66 ng/kg/min; P less than 0.005), and a significant (P less than 0.01) shift to the left of the relationship between norepinephrine-induced changes in mean arterial pressure and concomitant changes in plasma norepinephrine. In contrast, the relation between stepwise increasing plasma angiotensin II levels and induced changes in diastolic blood pressure or plasma aldosterone did not differ significantly between the two study groups. These findings delineate a distinct abnormality which may often occur in normotensive offspring of hypertensive families. It is characterized by a selectively disturbed noradrenergic blood pressure control in the presence of a normal angiotensin-mediated blood pressure and aldosterone regulation.

Effects of sodium chloride on pregnant sheep with reduced uteroplacental perfusion pressure

This study investigated the effects of NaCl supplementation (5 mEq/kg/day) on the arterial pressure of pregnant and nonpregnant sheep with and without reduction of uteroplacental perfusion pressure. In pregnant sheep receiving NaCl supplementation during the third trimester, reduction of aortic pressure caudal to the kidneys to 65% of the upstream pressure (occlusion) caused a progressive increase in mean arterial pressure from 89 +/- 3 to 110 +/- 3 mm Hg over 2 weeks. Occlusion was accompanied by a decrease in urine flow. Six of seven sheep died or were killed because of severe respiratory distress. No abnormalities were detected in nonpregnant sheep or pregnant sheep receiving NaCl supplementation only. Pregnant sheep that were occluded but received no supplementary NaCl did not become hypertensive but aborted about 2 weeks after occlusion. These results indicate that reduction of uteroplacental perfusion pressure causes hypertension in NaCl-supplemented pregnant sheep but not in sheep receiving a normal, low sodium diet.

Dietary and pharmacological alterations in endogenous angiotensin II: effect on noradrenaline pressor responsiveness in the rat

Rats were placed on either a low sodium intake (low sodium diet 0.025% dry weight, tap water for drinking) or a high sodium intake (normal sodium diet 0.45% dry weight, 0.9% saline for drinking) for 10 days. The pressor-response curve to angiotensin II in rats previously on a high sodium intake was shifted to the left of that found in rats previously on a low sodium intake. Suppression of endogenous angiotensin II formation with captopril (0.3 mg kg-1) or acute volume repletion (3% body wt per 30 min) resulted in a significant parallel shift of the pressor-response curve for angiotensin II to the left in the low salt group. In the high salt group captopril produced a similar but smaller parallel shift of the dose-response curve to the left. Similar manipulation of endogenous angiotensin II concentrations with high and low salt intake plus captopril treatment or acute volume repletion, produced no alterations in the pressor response for noradrenaline. The attenuated in vivo response to angiotensin II in the low salt intake group may be explained in part by the suppressed vascular sensitivity to angiotensin II in this group, as measured in the isolated perfused kidney of the rat. In kidneys from rats previously on a low sodium intake, an enhanced maximal vasoconstrictor response to noradrenaline was observed as compared to kidneys from high sodium intake rats. These results indicate that, whereas alterations in endogenous angiotensin II concentrations within physiological limits affects the response to exogenous angiotensin, there is little if any effect on the pressor response to noradrenaline.

Pressor factors and responsiveness in hypertension accompanying diabetes mellitus

Hypertension accompanying diabetes mellitus may involve abnormalities in at least two major blood pressure-regulating systems: the body sodium-fluid volume state and cardiovascular reactivity. In metabolically stable nonazotemic diabetes, exchangeable sodium is increased by 10% on average, regardless of age, insulin dependence or nondependence, or the presence or absence of diabetic retinopathy or clinical nephropathy (proteinuria greater than or equal to 0.3 g/24 hr). Possible contributing mechanisms include renal sodium retention and an extravascular shift of fluid and sodium; intracellular accumulation is not excluded. Circulatory volume is normal or low and the total exchangeable sodium/blood volume ratio increased. In hypertensive diabetes, the latter abnormality is particularly pronounced; systolic pressure tended to correlate with exchangeable sodium (r = 0.47, p less than 0.001) and diastolic pressure with the plasma sodium/potassium ratio (r = 0.25, p less than 0.05). Plasma aldosterone, renin, epinephrine, and norepinephrine levels are generally normal or sometimes low in metabolically stable nonazotemic diabetic patients with normal or high blood pressure; the plasma clearance of norepinephrine also appears to be unaltered. The cardiovascular pressor responsiveness to norepinephrine is often exaggerated relative to concomitant plasma concentrations, regardless of age, type of antidiabetic treatment, or presence or absence of diabetic retinopathy, peripheral neuropathy, or high blood pressure. Pressor responsiveness to angiotensin II also may sometimes be increased relative to plasma renin levels. Sodium retention and diabetic vasculopathy of resistance vessels could be important complementary mechanisms of hyperreactivity. In diabetes with mild hypertension, diuretic treatment restored exchangeable sodium, norepinephrine pressor responsiveness, and blood pressure toward normal. Thus sodium retention and cardiovascular hyperreactivity tend to occur even at the normotensive, nonazotemic stage of diabetes and may concomitantly predispose for the frequent development of hypertension in the diabetic population.

Transient enhancement of sympathetic nervous system activity by long-term restriction of sodium intake

To further investigate the relationship between salt intake and sympathetic nervous system activity, the short- and long-term effects of a low-salt diet (40 meq/day) were assessed in 10 normal subjects. Measurements of hemodynamic, hormonal, and other parameters were obtained on the day preceding institution of the low-salt diet (day 0) and on days 4, 7, 30, and 60 of the diet. Urinary sodium excretion was 178 +/- 10 meq/24 hr on day 0 and 31 +/- 4, 38 +/- 4, 45 +/- 6, and 47 +/- 7 meq/24 hr on days 4, 7, 30, and 60, respectively (all p less than .001 compared with day 0). Blood pressure, urinary potassium, serum electrolytes, and cardiac function (as assessed by echocardiography) were not modified by the 2 month low-salt diet. Plasma renin activity and plasma aldosterone were significantly elevated above control values throughout the entire period of the low-salt diet. In contrast, plasma norepinephrine concentration increased significantly only on days 4 and 7 (from 253 +/- 20 pg/ml on day 0 to 495 +/- 32 pg/ml, p less than .001, and 347 +/- 22 pg/ml, p less than .05, respectively), returning to baseline at days 30 (280 +/- 18 pg/ml) and 60 (262 +/- 18 pg/ml). Changes in plasma epinephrine paralleled those observed for norepinephrine. Similarly, resting heart rate and the blood pressure response to isometric exercise were significantly increased only on days 4 and 7 of the low-salt diet. These results suggest that sympathetic nervous system activity is enhanced only transiently during a sustained reduction in sodium intake.

Reactivity to norepinephrine and effect of sodium on blood pressure during weight loss

Eighteen moderately obese middle-aged men with untreated mild hypertension were randomized to two groups and placed on a low energy diet regimen for 9 to 11 weeks. In Group I (n = 10) the amount of sodium chloride in the diet maintained the urinary sodium excretion at the predieting level. Mean body mass was reduced by 9.1 +/- 0.7 (SEM) kg. Mean intra-arterial pressure showed no significant change. There were significant decreases in heart rate (p less than 0.05) and urinary norepinephrine excretion (p less than 0.05) but not in plasma concentration of norepinephrine. In Group II (n = 8) energy as well as sodium intake was restricted, with a 95 +/- 22 mmol/24 hour reduction of urinary sodium excretion. Body mass decreased by 9.3 +/- 1.1 kg, and mean arterial pressure decreased by -18.9 to -4.3 mm Hg (95% confidence interval). There were also significant reductions in heart rate (p less than 0.001) and plasma norepinephrine concentrations (p less than 0.01) but not in urinary norepinephrine excretion. The pressor response (mean arterial pressure) to norepinephrine infusion at different dose rates was significantly elevated (p less than 0.05) in Group I during dieting in comparison with baseline. The blood pressure response to norepinephrine during dieting in patients in Group II was not changed from baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood pressure and heart rate responses to mental stress in spontaneously hypertensive (SHB) and normotensive (WKY) rats on various sodium diets

Normotensive (WKY) and hypertensive rats (SHR) were, from 5 to 12 weeks of age, given 'low' (LNa), 'control' and 'high' (HNa) Na diets (0.5, 5 and 50 mmol X 100 g-1 food, respectively, during weekly recordings of body weight, conscious indirect systolic blood pressure (SBP) and heart rate (HR). During the last week, mean arterial pressure (MAP) and HR responses to standardized stress stimuli (air jet) were recorded before and after sequential cardiac nerve blockade. While resting, SBP was about equal in all WKY groups, but it was significantly reduced in SHR-LNa (152 mmHg versus 174 and 178 mmHg in SHR controls and HNa; P less than 0.05). In both LNa groups HR was elevated nearly 25% compared with controls, being in SHR 513 versus 419 bpm (P less than 0.01) and in WKY 489 versus 393 bpm (P less than 0.01). Cardiac nerve blockade indicated that this HR elevation was about equally due to elevations of sympathetic activity and 'intrinsic' pacemaker activity. SHR-LNa also showed attenuated MAP elevations to acute mental stress. There were, however, no significant differences between groups concerning haematocrit or plasma Na-K levels. The results suggest that SHR have a greater salt requirement than WKY, as Na restriction to one-tenth of normal led to a considerable MAP reduction in SHR despite compensatory sympathetic activation, and also to attenuated pressor responses to mental stress. Further, the cardiovascular effects in SHR were much more extensive when on a low-Na diet than when Na intake was increased tenfold above normal.

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.

Adrenergic activity and peripheral hemodynamics in relation to sodium sensitivity in patients with essential hypertension

In 25 outpatients with essential hypertension, sodium sensitivity, defined as the difference in mean arterial pressure (delta MAP) between 2 weeks of high-sodium (300 mmol per day) and 2 weeks of low-sodium (LS) intake (50-100 mmol per day), was studied in relation to the plasma norepinephrine (NE) level, NE release, and pressor response to intravenous NE. In addition, forearm blood flow (FBF) was measured by plethysmography. There were two control periods of regular sodium intake, one of 4 weeks' duration at the beginning of the study and one of 2 weeks' duration at the end. The delta MAP ranged from +18 to -8 mm Hg. The eight patients in whom delta MAP was greater than 10 mm Hg were regarded as salt-sensitive. When compared with salt-insensitive subjects, salt-sensitive patients had higher plasma NE levels in the control period (p less than 0.05) and after 2 weeks of HS intake (p less than 0.01). Sodium sensitivity was directly related to the change in plasma NE between the HS and LS periods (p less than 0.001). The NE release decreased in salt-insensitive subjects whereas it increased in salt-sensitive patients between the LS and HS periods. Changes in NE release were directly related to sodium sensitivity (p less than 0.05). The pressor response to NE was not significantly influenced by changes in sodium intake. The FBF fell in salt-sensitive patients and increased in salt-insensitive subjects between the LS and HS periods. Sodium sensitivity was directly related to the change in forearm vascular resistance (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma noradrenaline kinetics in humans

Recently developed radiotracer methods for measuring the overall rate of release of noradrenaline to plasma, for the body as a whole, can be used to estimate 'total sympathetic nervous system activity' in humans. These techniques find application in clinical studies of sympathetic nervous physiology and pharmacology. The inherent weakness of any biochemical test of global sympathetic tone such as this lies in the fact that sympathetic nervous system responses typically show regional differentiation. Biochemical indices of overall sympathetic activity are insufficiently discriminating to delineate patterns of sympathetic nervous response, representing instead an algebraic sum of all regional increases or decreases in sympathetic tone. Modification of the whole-body radiotracer methodology enables organ-specific sympathetic nervous system activity to be estimated, from measurements of regional release of noradrenaline to plasma. This should facilitate investigation of possible sympathetic pathophysiology in disease states. Illustrative of potential application of the method are preliminary findings of increased renal sympathetic nervous tone in young patients with essential hypertension, and of selective activation of sympathetic nerves to the kidney by diuretics.

Left ventricular mass reduction during salt depletion in arterial hypertension

Long-term therapy with antihypertensive agents that reduce sympathetic nervous system activity has been demonstrated by echocardiographic measurements to reverse left ventricular hypertrophy. This investigation evaluated the effects of salt depletion obtained by both chlorthalidone (25 mg/day) and severe restriction of salt intake (about 1016 mg Na+/day) on left ventricular mass (LVM) in as short a time as 12 weeks. Before the study, the patients had been off medication and on a balanced diet without salt restriction for at least 2 weeks; they were then randomly allocated to either the diuretic or low-salt regimen for 6 weeks and finally to alternative treatment according to a crossover model. Blood pressure, body weight, myocardial mass, and noninvasive measurements of left ventricular function (LVF) were determined at baseline and at the end of both periods of treatment. Results were evaluated by two-way analysis of variance in randomized blocks. Systolic and diastolic blood pressure and LVM were significantly and similarly reduced by diuretic therapy or salt restriction. A significant correlation was demonstrated between noninvasive measurements of LVM, expressed as cross-sectional area, and systolic blood pressure. No impairment of LVF could be detected over the treatment period.

Measurement of total and organ-specific norepinephrine kinetics in humans

A variety of biochemical tests, most notably measurement of the plasma concentration of norepinephrine, have been used to quantify overall sympathetic nervous system activity in humans. Plasma norepinephrine values provide a fallible index of sympathetic activity in that they are dependent in part on the rate of removal of norepinephrine from plasma. Measurement of the rate of release of norepinephrine to plasma is a better guide to overall sympathetic nervous tone because it avoids this confounding influence of norepinephrine plasma clearance. The overall norepinephrine spillover measurement, however, suffers from one major limitation: the sources of the released norepinephrine are not identified. Recently developed radiotracer techniques allow the estimation of regional sympathetic nervous activity from measurements of the organ-specific norepinephrine spillover rate. We find that the lungs are the main source of norepinephrine release to plasma, with mean pulmonary norepinephrine spillover of 159 ng/min constituting 40% of total norepinephrine release. Pulmonary norepinephrine release exceeded the combined norepinephrine spillover from the heart (3%), kidneys (17%), and hepatomesenteric circulation (8%).

Hemodynamic and endocrine changes associated with potassium supplementation in sodium-loaded hypertensives

To clarify the mechanism by which potassium (KCl) protects against the blood pressure rising action of sodium (NaCl), we studied the effects of KCl loading in patients with idiopathic hypertension who, after a period of NaCl restriction, partook of a high NaCl diet. Eleven patients who had taken the KCl supplement (96 mEq/day) during the high NaCl period showed lesser mean blood pressure (MAP) rise with changes in NaCl intake from 25 to 250 mEq/day than 12 patients who had not taken the KCl supplement (p less than 0.001). With a high NaCl diet, the KCl-supplemented patients retained less NaCl, gained less weight, and showed a lesser increase in plasma volume and cardiac output than the non-KCl-supplemented ones. Overall, the increase in blood pressure levels during the high Na diet correlated directly either with changes in plasma volume (p less than 0.05) or with changes in cardiac output (p less than 0.01). The results suggest that KCl may prevent a rise in blood pressure with NaCl loads in hypertensive patients by attenuating the increase in cardiac output, mainly as a result of the natriuresis. Furthermore, plasma norepinephrine was measured to estimate the sympathetic activity, since the sympathetic nervous system is known to control urinary NaCl excretion. From the low NaCl diet to Day 3 of the high NaCl diet, plasma norepinephrine was significantly (p less than 0.01) decreased in the KCl-supplemented patients, whereas it remained unchanged in the non-KCl-supplemented ones.(ABSTRACT TRUNCATED AT 250 WORDS)

Salt sensitivity in humans is linked to enhanced sympathetic responsiveness and to enhanced proximal tubular reabsorption

If high sodium intake is involved in the pathogenesis of essential hypertension, the effects of changing the sodium intake should be demonstrable in the susceptible part of the normotensive population. Therefore, we have investigated the effects of moderate salt restriction in 52 young normotensive subjects with and without a family history of hypertension; 22 (42%) responded to moderate salt restriction (200 to 50 mmol/day) over 2 weeks, with a significant fall in blood pressure shown by continuous automatic blood pressure recordings. Accordingly, these subjects were classified as salt-sensitive, and the remainder as salt-resistant. Compared to salt-resistant subjects, salt-sensitive subjects showed a 2.5-fold higher incidence of a positive family history of hypertension (p less than 0.01), and a significantly higher blood pressure and lower salivary sodium concentration during the usual high sodium diet. Although there were no differences in Na,K-ATPase activity and in Na-K cotransport of erythrocytes, the pressor response to infused norepinephrine in salt-sensitive subjects was double that of salt-resistant subjects independent of the diet and this was linked to indirect evidence for enhanced proximal tubular sodium reabsorption. On the usual high sodium diet, 40% of the normal population may be salt-sensitive and prone to develop hypertension. Hypersensitivity to catecholamines (genetically determined?) may be the cause of salt sensitivity. A low sodium concentration in saliva deserves further study as a simple screening test to identify salt-sensitive subjects.

Disturbed noradrenergic blood pressure control in normotensive members of hypertensive families

The possible influence of a family history of hypertension on some variables of adrenergic blood pressure regulation was assessed. Blood pressure, heart rate, plasma renin activity, adrenaline and noradrenaline concentrations, and plasma or urinary electrolyte estimations did not differ significantly between two groups of normotensive subjects matched for age and sex with and without a family history of hypertension. Compared with subjects without a family history, however, an appreciably decreased pressor dose of infused noradrenaline, a distinct shift to the left in the relation between noradrenaline induced changes in mean arterial pressure and concomitant plasma noradrenaline concentrations, and an enhanced pressor response to given increases in plasma noradrenaline concentrations occurred in the group with a family history. These findings suggest that an imbalance between cardiovascular noradrenaline responsiveness and circulating noradrenaline is a common familial disturbance which could possibly predispose to the development of essential hypertension.

Low sodium diet augments plasma and tissue catecholamine levels in pithed rats

Plasma and tissue (cardiac, vascular, renal, and adrenal) catecholamine concentrations were measured in pithed male Wistar rats maintained on low (10 mEq/kg diet), basal (115 mEq/kg diet), or high (1200 mEq/kg diet) sodium test diets for five weeks. Significant differences in catecholamine disposition were observed only in response to sodium restriction; responses to basal and high sodium intakes were consistently similar. Baseline plasma catecholamine levels (p less than 0.01) as well as those in response to stimulation of the entire sympathetic outflow at 4 Hz were markedly enhanced in low sodium rats (p less than 0.001). The facilitation of stimulation-induced increments in plasma norepinephrine levels in low sodium rats may be related to the finding that norepinephrine content was also elevated in noradrenergically innervated tissues (atria, ventricles, mesenteric artery, and kidneys) (p less than 0.01). Adrenal catecholamine levels, however, were not affected by dietary sodium restriction. Despite the peripheral catecholamine changes associated with a low sodium intake, pressor and tachycardic responses to sympathetic nerve stimulation were similar across dietary sodium groups. The results indicate that a low sodium intake enhances plasma and tissue catecholamine levels, adaptations that may be important in the maintenance of sympathetic responsiveness.

Plasma norepinephrine and dietary sodium intake in normal subjects and patients with essential hypertension

To evaluate the relationship between sodium intake and the activity of the sympathetic nervous system in patients with essential hypertension, plasma catecholamine levels were measured in 49 essential hypertensive patients and 38 age-matched normal subjects under regular-, high-, and low-sodium diets (mean 24-hour sodium excretions; 116 +/- 8, 267 +/- 29, 31 +/- 7 mEq/day, respectively). The levels of plasma norepinephrine were significantly (p less than 0.01) higher in hypertensive patients than in normal subjects. However, they were significantly reduced by high-sodium intake and increased by low-sodium intake in both patients and controls. The percent decrease and change in the absolute plasma norepinephrine levels from low- to high-sodium states were greater in normal subjects than in the hypertensive patients. The results are interpreted as indicating that an abnormal relationship exists between sodium intake and the activity of sympathetic nervous system in patients with essential hypertension.

Dietary sodium and potassium-induced transient changes in blood pressure and catecholamine excretion in the Sprague-Dawley rat

When Sprague-Dawley derived rats were changed from a chow type diet to a moderately high sodium diet, rapid transient changes in blood pressure (BP) and catecholamine excretion were observed. After 1 dietary week, BP increased from 122 +/- .1 mm Hg to approximately 145 mm Hg (p less than 0.001), and there was a concomitant 20% reduction in urinary norepinephrine (UNEV) and epinephrine (UEV) excretion (p less than 0.05). Heart rates were reduced (p less than 0.05). These data suggest that sodium-induced increases in BP were initially associated with suppressed sympathetic nervous system activity. During dietary Weeks 2 and 3, some animals had a persistent moderate elevation in BP (BP less than or equal to 150 mm Hg), while others developed more severe increases. UNEV in moderately hypertensive animals returned to control levels during this period; but UEV and heart rates remained suppressed. UNEV in severely hypertensive animals exceeded (13% +/- 3%, p less than 0.05) that of controls. This increase coincided with their most severe hypertension (171 +/- 1 mm Hg, p less than 0.001). UE values and heart rate data indicate that systemic adrenergic tone was likely suppressed at this time and that the increased UNEV was renal in origin. By dietary Week 4, the BP of severely hypertensive animals had begun to fall, and indices of sympathetic nervous system tone were indistinguishable among all groups. Inclusion of a dietary potassium supplement ameliorated the development of hypertension only in those animals that became severely hypertensive, and appeared to prevent the early suppression of indices of sympathetic activity.

Progressive hypertension in dogs by avoidance conditioning and saline infusion

A group of dogs was trained on a free-operant avoidance-conditioning task that evoked acute increases in arterial pressure and heart rate during each of three daily 30-minute sessions. After 15 days of exposure to this procedure under conditions of normal sodium intake, 24-hour mean levels of arterial pressure remained unchanged. Another group of dogs received continuous intrarterial infusion of isotonic saline at a constant rate of 185 mEq/24 hrs for 15 days, but no avoidance sessions. Again, 24-hour mean levels of arterial pressure did not change significantly. However, 24-hour mean levels of systolic (19.5 +/- 6.2 mm Hg) and diastolic (13.7 +/- 2.9 mm Hg) pressure rose progressively over a 15-day period in a third group of dogs exposed concurrently to the avoidance schedule and saline infusion procedure. The progressive hypertension was accompanied by no consistent changes in heart rate. These experiments indicate that behavioral stress can potentiate sodium hypertension and provide a new method for the study of physiological and behavioral factors in long-term blood pressure control.

Stress and high sodium effects on blood pressure and brain catecholamines in spontaneously hypertensive rats

The following experiments were designed to determine if territorial stress, dietary sodium (Na), or the combination of stress and Na effect the rate of development of hypertension in the spontaneously hypertensive rat (SHR 4-18 wks) and if central catecholamines (C) were altered by these treatments. BP was significantly elevated from 2-8 weeks of stress treatment as compared to SHR controls. Norepinephrine (NE) levels in the nucleus tractus solitarius and amygdala (A), and dopamine (D) levels in the hippocampus and A showed significant elevations in the stressed group. High Na (3%) treatment combined with stress treatment produced an even further BP increase and elevated D levels in the amygdala, and elevated NE levels in the area postrema as compared to control SHR's. Selected brain C variables were able to correctly classify animals into high and low BP groups with 90-100% accuracy. Our data support the concept that there are important stress and Na effects upon brain neurochemistry which influence the development of hypertension in the SHR.