Volume-dependent essential and steroid hypertension

The mTOR-inhibitor everolimus reduces hypervolemia in patients with primary aldosteronism

BACKGROUND

We recently showed in a proof-of-concept study that treating individuals with primary aldosteronism with the mTOR-inhibitor everolimus decreases home blood pressure and renin suppression overall, and markedly reduces aldosterone levels in a subset of individuals. Based on these findings, the question arose whether the effects of everolimus were also mediated via aldosterone-independent mechanisms. Here, we undertook an exploratory, secondary analysis of above-mentioned study to comprehensively investigate how everolimus impacted the hemodynamic status of the study participants, which in turn could elucidate these mechanisms.

METHODS

Hemodynamic parameters were measured in study participants with primary aldosteronism at baseline, after treatment with everolimus 0.75 mg orally twice daily for 2 weeks and after a 2-week wash-out. Of the 14 participants, 10 participants had complete data sets for peripheral and central blood pressure, heart rate and pulse wave velocity, and 7 participants had complete data sets for cardiac index, inotropic state index, left stroke work index and stroke systemic vascular resistance index that could be analyzed. Parameters were acquired by brachial oscillometry (Mobil-o-graph PWA) and thoracic electrical bioimpedance (HOTMAN® System).

RESULTS

After treatment with everolimus, peripheral (P=0.049) and central (P=0.037) diastolic blood pressure, as well as hypervolemia (P=0.008) were significantly decreased. Likewise, peripheral (P=0.073) and central systolic blood pressure (P=0.166) trended downwards.

CONCLUSIONS

Everolimus lowers central and peripheral blood pressure in individuals with primary aldosteronism, possibly by decreasing primary aldosteronism-induced hypervolemia and preload.

Long COVID: post-acute sequelae of COVID-19 with a cardiovascular focus

Emerging as a new epidemic, long COVID or post-acute sequelae of coronavirus disease 2019 (COVID-19), a condition characterized by the persistence of COVID-19 symptoms beyond 3 months, is anticipated to substantially alter the lives of millions of people globally. Cardiopulmonary symptoms including chest pain, shortness of breath, fatigue, and autonomic manifestations such as postural orthostatic tachycardia are common and associated with significant disability, heightened anxiety, and public awareness. A range of cardiovascular (CV) abnormalities has been reported among patients beyond the acute phase and include myocardial inflammation, myocardial infarction, right ventricular dysfunction, and arrhythmias. Pathophysiological mechanisms for delayed complications are still poorly understood, with a dissociation seen between ongoing symptoms and objective measures of cardiopulmonary health. COVID-19 is anticipated to alter the long-term trajectory of many chronic cardiac diseases which are abundant in those at risk of severe disease. In this review, we discuss the definition of long COVID and its epidemiology, with an emphasis on cardiopulmonary symptoms. We further review the pathophysiological mechanisms underlying acute and chronic CV injury, the range of post-acute CV sequelae, and impact of COVID-19 on multiorgan health. We propose a possible model for referral of post-COVID-19 patients to cardiac services and discuss future directions including research priorities and clinical trials that are currently underway to evaluate the efficacy of treatment strategies for long COVID and associated CV sequelae.

Influence of sodium intake on hydrochlorothiazide-induced changes in blood pressure, serum electrolytes, renin and aldosterone in essential hypertension

To determine the influence of dietary sodium intake on the effects of hydrochlorothiazide (HCT) on blood pressure (BP), serum electrolytes, renin and aldosterone, nine male patients with uncomplicated essential hypertension were studied during the following therapeutic regimes: 1) sodium restriction alone (50 mmol/day), 2) sodium restriction combined with HCT (50 MG TWICE DAILY), 3) HCT alone, and 4) sodium restriction combined with HCT. Low sodium diet alone and HCT alone lowered BP to the same extent. The combination of HCT and sodium restriction had no extra effect on supine BP, but elicited complaints of dizziness and weakness in each patient, and overt orthostatic hypotension in three cases. Sodium restriction during HCT treatment caused hyponatraemia and aggravated hypokalaemia. Hyponatraemia could not be accounted for solely by changes in cumulative sodium balance. Plasma renin concentration rose markedly during the combined treatment. Plasma aldosterone was normal during HCT alone, but elevated when HCT was combined with sodium restriction. These results cast some doubt on the therapeutic value of prescribing a low sodium diet to patients with essential hypertension treated with thiazide diuretics. Overactivity of the renin-angiotensin-aldosterone system during this regime might explain both the lack of a beneficial effect on BP and the adverse influence on serum potassium.

Salt sensitivity in hypertensive type-1 diabetes mellitus

As sodium retention has been proposed as a causal factor in the development of hypertension in diabetic patients, a high incidence of salt sensitivity has been suggested. To evaluate the influence of dietary sodium intake on blood pressure, casual and 24-h blood pressure was measured in 30 hypertensive type-1 diabetic patients aged 24-67 (mean 46) years while they were on habitual diet, after 6 days of low-sodium diet (50 mmol/day), and after 6 days of high-sodium diet (250 mmol/day). Nine patients (30%) who increased their 24-h mean blood pressure by more than 10% when going from low- to high-sodium intake were classified as salt sensitive; the others as salt resistant. The salt sensitive group had a significantly lower urinary excretion of dopamine at baseline, and a higher diuresis and a more pronounced decrease in 24-h blood pressure during salt depletion (all p < 0.01). Low-sodium diet reduced casual and 24-h blood pressure by 4% in the total study population compared with 9% in the salt sensitive group (p < 0.01). There was no difference in glomerular filtration rate, filtration fraction, proteinuria or urinary sodium excretion between the groups.

CONCLUSIONS

Sodium restriction more effectively reduces blood pressure in the salt sensitive minority of hypertensive type-1 diabetic patients irrespective of renal function. The incidence of salt sensitivity is not increased in hypertensive type-1 diabetic patients compared with essential hypertensive patients.

Systemic and regional hemodynamics in patients with salt-sensitive hypertension

Twenty-two patients with normal plasma renin and essential hypertension were classified as "salt-sensitive" (SS) (n = 9) or "non-salt-sensitive" (NSS) (n = 13) from an increase in mean blood pressure with changes in sodium intake from 25 to 250 meq/day. With the high sodium diet, the SS patients gained more weight (p less than 0.05), retained more sodium (p less than 0.05), and had a greater increase in cardiac output (p less than 0.05). Despite the markedly increased cardiac output, systemic vascular resistance did not change with sodium loads in the SS patients, whereas the NSS patients had a significant decrease in systemic vascular resistance. Thus, the greater increase in blood pressure with sodium loads in SS patients can be attributed not only to an increase in cardiac output, possibly resulting from greater sodium retention, but also to inappropriately elevated systemic vascular resistance. Concomitant with a greater increase in cardiac output, the SS patients had a greater increase in forearm blood flow with sodium loading than the NSS patients (p less than 0.02). In contrast, blood flow to the kidney and the liver was not significantly changed in either group; renal (p less than 0.05) and hepatic (p less than 0.01) vascular resistance increased significantly in SS patients but remained unchanged in NSS patients. Thus, evidence presented suggests that the greater increase in blood pressure with sodium loads seems to be characterized by a very inhomogenous distribution of local flow and resistance in SS patients; renal and hepatic blood flow remains essentially unchanged and skeletal muscle blood flow receives almost all of the increase in cardiac output. Moreover, systemic vascular resistance changes did not reflect the resistance of individual beds because vasoconstriction appeared in the kidney and the splanchnic area but was masked by prominent vasodilation in the skeletal muscle. Because this hemodynamic pattern is similar to the pattern evoked during defense reaction, it is suggested that sympathetic overactivity on a selective basis might be involved in the impaired renal function for sodium excretion and the increase in blood pressure with sodium loads in SS patients.

Corcoran lecture: the case for or against salt in hypertension. Arthur Curtis Corcoran, MD (1909-1965). Tribute and prelude to Corcoran Lecture of 1988

Salt intake in excess of body needs has long been considered a factor in the genesis and maintenance of human hypertension; the mechanism is salt retention due to faulty renal excretory efficiency. This discussion reviews clinical studies that make a case either for or against the salt hypothesis. Included is a summary of recent experiences with 4 days of salt depletion and 3 days of salt loading in 96 normotensive control subjects and 40 hypertensive patients. These studies were done to test the hypothesis that salt-sensitive blood pressure changes are quantitatively related to sodium balance. However, we found no statistically significant relation between arterial pressure changes and sodium lost during salt depletion or retained during salt loading. The failure of that hypothesis prompted a study of the known factors that control arterial pressure by using multidimensional response surface modeling for changes produced by salt loading. The analysis indicated that in these experiments salt-sensitive blood pressure changes of hypertensive patients were controlled differently than those of normotensive subjects. In the hypertensive group, the changes were highly predictable by combinations of variables, which featured plasma aldosterone, norepinephrine, and epinephrine. In the normotensive group, the changes were less predictable; fewer of the factors were involved, and plasma renin activity was the featured variable. These findings and results of studies done over the past 50 years indicate that salt-dependent hypertension is controlled by many factors and is not a strict correlate of salt intake.

Relationship of sodium balance to arterial pressure in black hypertensive patients

To investigate the quantitative importance of sodium balance to arterial pressure changes produced by changes in sodium intake, we studied normotensive white and black subjects and hypertensive black patients with two protocols. Protocol 1 used a 3-day control period with a 150 mEq sodium intake/day followed by 4 days of salt depletion (SD) with a diet providing 9 mEq/day of sodium and furosemide, 1 mg/kg, given the first day and then 3 days of salt loading (SL), during which 25 mL/kg of isotonic sodium chloride solution was given intravenously each day (3.88 mEq sodium/kg/day). In protocol 2, the sequence of sodium intake changes was reversed. For both protocols, sodium balance was calculated by subtracting urinary sodium excretion from sodium intake and expressed in mEq/kg, either positive or negative. In protocol 1, the hypertensives had statistically significant changes in arterial pressure with changes in salt intake, and they also lost more sodium than normotensives during SD. In protocol 2, blacks, both normotensives and hypertensives, had statistically significant pressure changes with both SL and SD, and black hypertensives retained less sodium during SL than either normotensive group. Spearman correlations showed no relationship between sodium balance and mean arterial pressure, suggesting that salt-sensitive hypertension results not from the magnitude of sodium retention, but from the pressor mechanisms evoked.

Plasma and urinary catecholamines in salt-sensitive idiopathic hypertension

Nineteen patients with normal renin idiopathic hypertension were arbitrarily classified as salt-sensitive or salt-resistant depending on whether their mean arterial pressure did or did not increase by 8% or more when sodium intake was increased. The responses of the two subsets and of five normal subjects to sodium intakes of 9, 109, and 249 mEq/day given for 7 days were as follows: The salt-sensitive subjects retained more sodium than normal and plasma or urinary norepinephrine did not decrease when they were given a high sodium intake; urinary dopamine was normal but did not increase normally when sodium intake was increased. The salt-resistant subjects excreted sodium normally and plasma and urinary norepinephrine was decreased by 30 and 37%, respectively, when they were given a high sodium intake; urinary dopamine was supernormal and did not increase further when sodium intake was increased. Cumulative sodium retention during the high sodium intake was directly related to the percentage of change in plasma norepinephrine in the hypertensive subjects, suggesting that renal adrenergic activity was a factor in the impaired sodium excretion in the salt-sensitive patients. Cumulative sodium retention and the percentage of change in plasma norepinephrine were inversely related to urinary dopamine in the hypertensive subjects, suggesting that increased formation of dopamine in renal and neural tissue in the salt-resistant subjects may have been responsible for the differences between the subsets in renal and adrenergic responses to a high sodium intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Excessive sodium retention as a characteristic of salt-sensitive hypertension

To investigate the possibility that salt-sensitive hypertensives have deficient sodium excretion, the sodium retained by 20 hypertensive patients during a salt load (SL = 3.88 mEq/Kg/day) was calculated for 3 days immediately after 4 days of sodium deprivation (SD = 9 mEq/d). Patients were divided into two groups by arterial pressure responses to SD: responders (N = 10) whose pressures became normal rapidly and averaged less than 140/90 during SD and nonresponders (n = 10) whose pressures were not affected. Sodium retention (mEq/Kg) during SL was calculated as cumulative sodium intake minus cumulative urinary sodium divided by body weight. Responders retained more sodium during SL than nonresponders (3.71 +/- 0.96 [SD] vs. 2.52 +/- 1.05 mEq/Kg, p less than 0.02). This could not be explained by a measurable decrease in filtered sodium load since creatinine clearance was the same in each group. Neither was it associated with differences in plasma renin activity (PRA) or aldosterone excretion rates (AER). Whereas PRA was significantly lower in responders at the end of SD, AER was not different; with SL, group values were equally suppressed. Also sodium excretion was not correlated with arterial pressure except in non-responders on the last day of SL. These data indicate that salt-sensitive hypertensives handle sodium differently than nonsalt-sensitive hypertensives.

The extrarenal effects of aldosterone on the distribution of extracellular fluid in conscious adrenalectomized-nephrectomized rats

In order to examine the extrarenal roles of aldosterone in cardiovascular homeostasis, the present study compared blood pressure, extracellular fluid volume (ECFV) and plasma volume (PV) in the three following groups: 10 nephrectomized (NX) rats, 10 nephrectomized-adrenalectomized (NX-AX) rats, and 10 NX-AX and aldosterone-treated (NX-AX-A) rats. Two-hundred and fifty micrograms of aldosterone, mixed with sesame oil, was given subcutaneously in the NX-AX-A rats. Mean arterial pressure (MAP) was recorded through previously implanted carotid catheters. ECFV and PV were measured using 35S-Na2SO4 and 131I-RISA, respectively, 24 h after the operation. These measurements were performed in an unanesthetized and unrestricted condition. MAP gradually increased in the NX group, while a gradual decrease was observed in the other groups. However, MAP was significantly higher in the NX-AX-A group than in the NX-AX group 6 h after the operation and thereafter. Changes in body weight were comparable in the three groups 24 h after the operation. ECFV and PV were both reduced in the NX-AX and the NX-AX-A groups as compared to the NX group (P less than 0.001 NX-AX vs NX, and P less than 0.05 and P less than 0.025 NX-AX-A vs NX, respectively). Although ECFV was comparable in the NX-AX and the NX-AX-A groups, PV was significantly greater in the NX-AX-A group than in the NX-AX group (P less than 0.05). There was a significant positive correlation between MAP and PV in the rats as a whole (r = 0.68, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood volume expansion among blacks: an hypothesis

Black persons are believed to have developed in a tropical environment and an expanded blood volume would have facilitated adaptation to such an environment. Throughout most of the first half of the life cycle blacks have slower heart rates than whites, and several lines of evidence suggest that heart rate is inversely related to blood volume. Review of blood volume studies in normotensive whites and normotensive blacks does not permit any conclusion concerning the blood volume hypothesis. Among patients with hypertension results of blood volume studies are inconsistent, but indirect evidence suggests that black patients with hypertension have greater plasma volume expansion than white patients with hypertension.

Sodium intake and exchangeable sodium in hypertensive rats

Exchangeable sodium, extracellular fluid volume and sodium intake were significantly higher in spontaneously hypertensive rats (SHR) than in normotensive controls. The increased exchangeable sodium was due to the expanded extracellular fluid sodium content. Two kidney one clip Goldblatt renal hypertensive rats develop thirst and high renin levels. When drinking saline the rats have markedly increased exchangeable sodium levels, but those drinking water did not. It is proposed that the exaggerated saline intake leads to a volume dependent component of the hypertension in both models. In the SHR both the salt appetite and the hypertension may be induced by angiotensin acting via central mechanisms.

Pathophysiology of essential hypertension. Role of the autonomic nervous system

The participation of the autonomic nervous system in hypertension is not restricted to increased cardiac action and peripheral vasoconstriction during periods of stress. The three major systems that are particularly involved in hypertension, the heart, brain, and kidneys, are interrelated in a multifaceted way by which all of them inform, interfere, and influence one another. The autonomic nervous system will play an important role in most types of hypertension whether these are volume-dependent, cardiogenically mediated, or related to stimulation of the renin-angiotensin system.

Comparison of propranolol or hydrochlorothiazide alone for treatment of hypertension. III. Evaluation of the renin-angiotensin system

In this study, the relation between renin activity and therapeutic response to hydrochlorothiazide or propranolol was studied. Patients with a diastolic blood pressure of 95 to 114 mm Hg were treated with propranolol (40 to 320 mg twice daily) or hydrochlorothiazide (25 to 100 mg twice daily). The initial renin profiles were: low, 56 percent (n = 300); normal, 33 percent (n = 174); high, 11 percent (n = 60). A greater incidence of low and fewer high renin profiles (p less than 0.001) were observed in blacks. After furosemide administration (40 mg intravenously), 55 percent of patients (n = 291) had a low renin response and 45 percent (n = 240) had a normal renin response. No correlation between renin profile and renin response was observed, although low renin response and low renin profile occurred more frequently in older patients. Hydrochlorothiazide administration resulted in a greater decrement in diastolic blood pressure (p less than 0.05) in the total group. Irrespective of renin activity, both hydrochlorothiazide and propranolol reduced diastolic blood pressure. When renin profile was considered, no significant variation in response to hydrochlorothiazide therapy was observed, and there was a greater reduction in diastolic blood pressure in the patients with a high renin profile receiving propranolol. In comparing therapeutic response, patients with a low renin profile had a better response to hydrochlorothiazide, and propranolol was more effective in patients with a high renin profile. The anticipated effect of therapy on plasma renin activity was observed. Although these results are consistent with a volume-vasoconstrictor analysis of hypertension, the results of therapy could not have been prejudged from renin profile or responsivity. The slight differences observed do not warrant the expense of renin determinations when a simple determination of therapeutic response is sufficient.

Physiologic regulation of arterial pressure. An overview

Research of the past 30 years has produced information showing the close interrelationships of neural mechanisms, the renin-angiotensin-aldosterone system, and salt balance as determinants of arterial pressure, both normal and elevated. Contemporary emphases are on central sites of neural regulation of arterial pressure, and an interesting sidelight of the conventional approaches is the possibility that the endorphin-enkephalin system may have a role in hypertension. Salt balance is critically important for people with salt-dependent hypertension; mechanisms of this dependency have not been defined but possible candidates are activation of the sympathetic nervous system, release of a natriuretic factor that causes vasoconstriction as well as salt loss, and renal-neural interactions.

Diuretic potency of combined hydrochlorothiazide and furosemide therapy in patients with azotemia

The effect of combined hydrochlorothiazide and furosemide therapy was studied in eight hypertensive patients with renal insufficiency who had poor response to either furosemide or hydrochlorothiazide alone. The study was divided into two parts. In part A, five patients had an inadequate response to furosemide in doses of 160 to 240 mg/day followed a strict protocol in order to compare the effect of increased doses of furosemide with combined hydrochlorothiazide-furosemide administration. All had azotemia, presumable from nephrosclerosis, and had serum creatinine concentrations ranging from 2.3 to 4.9 mg/dl. Four of the five patients had inadequate arterial pressure control, and the remaining patients had fluid retention from the administration of minoxidil. In all five patients, plasma volume was either increased or normal, despite long-term treatment with furosemide. Increasing the dose of furosemide to between 320 and 480 mg/day had only a modest additional diuretic effect, and plasma volume and arterial pressure were not significantly changed. Adding hydrochlorothiazide, 25 to 50 mg twice a day, produced a marked diuresis, and a significant reduction in weight, plasma volume and mean arterial pressure (p less than 0.025 for all three patients). In part B, combined hydrochlorothiazide-furosemide therapy was used to treat three additional patients who had an inadequate response to either diuretic alone. The results indicate that combined hydrochlorothiazide-furosemide is a potent diuretic regimen and is effective in many patients wit chronic renal failure who have a poor response to furosemide alone.

Hypertension in obese patients: hemodynamic and volume studies

Distinct hemodynamic and volume characteristics have been suggested for established hypertension in severe obesity, namely, a high cardiac output, and expanded blood volume, and a normal peripheral resistance. To evaluate whether hypertension in moderately obese patients represents a separate entity that can be defined by hemodynamic and volume profiles, we studied these in 50 such patients and compared results with those obtained in 59 nonobese essential hypertensives and 25 normal subjects. Both obese and nonobese hypertensives had a normal cardiac index (men, 2.8 +/- 0.1 vs 2.8 +/- 0.09 liter/min/m2; women, 2.9 +/- 0.1 vs 2.8 +/- 0.1 liter/min/m2, respectively) and similarly elevated total peripheral resistance (men, 47.1 +/- 2.3 vs 46.5 +/- 1.9 U . m2; women, 45.0 +/- 2.4 vs 44.0 +/- 1.3 U . m2, respectively) as compared to normals (cardiac index: men, 2.9 +/- 0.09 liter/min/m2, women, 3.4 +/- 0.2 liter/min/m2; total peripheral resistance: men, 29.4 +/- 1.0 U . m2, women, 28.3 +/- 2.8 U. m2). Volume measurements corrected to body surface area showed that both obese and nonobese hypertensive patients had lower blood volume (men, 2.6 +/- 0.05 vs 2.5 +/- 0.05 liter/m2; women, 2.2 +/- 0.05 vs 2.3 +/- 0.05 liter/m2, respectively) than normals (men, 2.9 +/- 0.08 liter/m2; women, 2.5 +/- 0.08 liter/m2). The results of this study suggest that hypertension in moderately obese subjects is similar in its hemodynamic and volume profiles to hypertension in the nonobese and that the presence of obesity does not alter the hemodynamic characteristics of established essential hypertension.

Cross-cultural variation in blood pressure: a quantitative analysis of the relationships of blood pressure to cultural characteristics, salt consumption and body weight

This study has analyzed the relationships of cross-cultural variation in blood pressure to cultural characteristics, salt consumption and body weight. The data used were blood pressures for adults in 84 groups, ratings of cultural characteristics (based on anthropological data and made by raters who had no knowledge of the blood pressure data) and, where available, salt consumption and body mass index (weight/height2). Blood pressures were higher and the slopes of blood pressure with age were greater in groups which had greater involvement in a money economy, more economic competition, more contact with people of different culture or beliefs, and more unfulfilled aspirations for a return to traditional beliefs and values. Blood pressures were also higher in groups for which the predominant family type was a nuclear or father-absent family, as opposed to an extended family. For Negroes, groups who were descended from slaves had higher blood pressures than other groups. The correlations between blood pressures and involvement in a money economy were substantial and significant even after controlling for level of salt consumption and, for men, also after controlling for body mass index. For men there were also significant partial correlations between blood pressure and salt consumption, controlling for type of economy. For women there were significant partial correlations between blood pressure and body mass index, controlling for type of economy. In conclusion, cross-cultural variation in blood pressure appears to be due to multiple factors. One contributory factor appears to be psychosocial stress due to cultural disruption, including the disruption of cooperative relationships and traditional cultural patterns which frequently occurs during economic modernization. In addition, both the protective effects of very low salt consumption in some groups and differences in body weight appear to contribute to cross-cultural variation in blood pressure.

Antihypertensive effect of riboflavin analogs in rats with mineralocorticoid-induced hypertension

This study investigated whether the riboflavin analogs, 7,8-dimethyl-10-formylmethyl isoalloxazine (FMI) and 7,8-dimethyl-10-(2'-hydroxyethyl) isoalloxazine (HEI), are effective antihypertensive agents in mineralocorticoid-induced or deoxycorticosterone acetate (DOCA)-salt hypertension. These studies are based on our previous observation tht aldosterone enhances the biosynthesis of renal flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) from riboflavin, and that FMI and HEI competitively inhibit conversion of riboflavin to FMN and reabsorption of Na+ in the kidney of adrenalectomized rats. When 1.6 mg of FMI or HEI were administered simultaneously with 3.0 mg of DOCA, the tail systolic blood pressure (SBP) of unanesthetized rats rose only to 136 +/- 5 mm Hg (standard error of the mean, SEM) compared to 163 +/- 5 mm Hg during DOCA therapy alone (p less than 0.0005). This hypotensive effect of FMI or HEI was noted after the fourth week of treatment and persisted through the ninth week. The rats tolerated the medication well and had no signs of riboflavin deficiency. DOCA administration alone resulted in a 24% increase in iliopsoas muscle Na+ concentration (p less than 0.0005), and a 0.8% increase in the water content of the muscle (p less than 0.025), suggesting a positive Na+ balance. Administration of FMI or HEI blunted the ability of DOCA to increase muscle Na+ concentration (p less than 0.025), water content (p less than 0.01). HEI treatment of the Kyoto strain of spontaneously hypertensive rats (SHR) did not lower their mean SBP. Thus it appears that the hypotensive actions of FMI or HEI are closely associated with their ability to modify the effects of mineralocorticoids on NA+ balance.

Hemodynamics of essential hypertension in young subjects

Cardiac output was determined in 42 young essential hypertensives (15 to 25 yrs); values ranged from 3.86 to 10.30 L./minute. These differences were not related to magnitude of volemia. Correlation of output to weekly blood pressure average (BPav) was not significant; its relationship to intraarterial pressure (BPia) was not significant in 21 patients aged 20 to 25 and of borderline significance in 13 aged 15 to 19. Blood pressure changes associated with the study (BPia--BPav) were also not consistently related to cardiac output. Six patients had systolic hypertension; only one had elevated stroke volume. These results outline as complex a picture in young essential hypertensives as in older subjects.

The toxicity of salt

The subject of sodium toxicity has been controversial for a long time. There is no question that the element can be noxious when consumed acutely in large quantities and there is little doubt as to cause and effect Conversely the consequences of mederate chronic sodium consumption are much harder to document. The effects are insidious and are subject to modification by a variety of environmental influences such as dietary potassium. In addition most studies of chronic sodium excess have dealt with elusive subject of "essential" hypertension. Interpretations of data have been very difficult, and conflicting reports have occurred. Nevertheless epidemiological, clinical, and animal studies show that chronic excess sodium ingestion acting upon a substrate of genetic susceptibility, is an important etiologic factor in essential hypertension and the expression of its sequelae. Positive correlations have also have been obtained between dietary salt and the incidence of stroke and gastric cancer. Dietary potassium appears to confer some degree of protection from the toxic properties of sodium through some unknown mechanism. Available evidence indicates that a suitable intake of salt for man might be approximately 3.5 g/day and probably less. Salt consumption in most developed countries ranges between 8 to 40 g/day, and modern methods of food processing and preparation deplete the protective potassium. The incidences of hypertension in these countries range between 15 to 40% of their populations, and it exacts a dreadful toll. Recognition of the toxic properties of sodium and knowledge of the mechanisms involved in its toxicity offer great possibilities in the area of preventive medicine It may be possible by the sorting out of hypertension-prone subjects and dietary intervention to prevent or minimize the development of hypertension in susceptible individuals. This says nothing of other aspects of sodium toxicity, of which we are largely ignorant.

The pressor response to angiotensin II in patients with low renin essential hypertension

The etiology of low renin essential hypertension (LREH) has not been established with certainty, but mineralocorticoid excess has been implicated frequently in its pathogenesis. The finding of several investigators of a normal exchangeable sodium space and extracellular fluid volume, however, does not support this hypothesis. To evaluate the possible role of sodium and water retention in LREH, the pressor response to infused angiotensin II (A II) was determined and compared to that of normal subjects and that of subjects with normal renin essential hypertension (NREH). This approach was based on the known suprasensitivity of vascular receptors to A II in situations in which sodium and water compartments are expanded as they are, for example, in proven hypermineralocorticoid states such as primary aldosteronism. In this study, we found that subjects with LREH demonstrated no increased pressor response to graded doses of A II; this suggests that LREH is not primarily mediated by sodium and water retention.

The effect of high-sodium and low-sodium intakes on blood pressure and other related variables in human subjects with idiopathic hypertension

Nineteen patients with hypertension in whom all known causes of blood pressure elevation had been ruled out were classified as "salt-sensitive" or "nonsalt-sensitive" from the changes in blood pressure with changes in sodium intake from 9 meq to 249 meq/day. With the diet containing 249 meq sodium per day, there were no statistically significant differences in plasma sodium, potassium, chloride, aldosterone, cortisol or renin activity, or in urinary potassium, aldosterone or 17-hydroxycorticosteroids between the two groups. The "salt-sensitive" patients retained more sodium on the high-sodium diet than did the patients who were not sensitive to salt ("nonsalt-sensitive"); accordingly, sodium induced more weight gain in the salt-sensitive patients.

Interrelations among blood pressure, blood volume, plasma renin activity and urinary catecholamines in benign essential hypertension

Interrelations among blood pressure, circulatory volume, plasma renin activity (PRA) and urinary catecholamine excretion rates were studied in normal subjects and in patients with benign essential hypertension. Mean plasma or blood volumes related to lean body mass, products of blood volume and the logarithm of PRA, and catecholamine excretion rates did not differ significantly between normal and hypertensive subjects. In both normal subjects and hypertensive patients, blood pressure levels correlated positively with the noradrenaline excretion rate (r = 0.40 and 0.36, respectively; p less than 0.025) but not with adrenaline excretion, circulatory volume or the volume-renin product. The logarithm of PRA correlated inversely with mean blood pressure in normal subjects (r = 0.40; p less than 0.001) but not in hypertensive patients; however, there was no convincing evidence for an inappropriate blood pressure-PRA relationship as a prominent feature in the hypertensive patients. PRA did not correlate with blood volume. Patients with low PRA relative to sodium excretion (21 per cent of hypertensive population) were consistently normovolemic, but they tended to be older and excreted less (p less than 0.025) adrenaline than patients with normal or high PRA. The patient subgroup with high PRA relative to sodium excretion (11 per cent of population) was hypovolemic (p less than 0.02); despite this, urinary sodium output was high (172 +/- 64 meq/24 hours). These data reveal no evidence for major roles of PRA, circulatory volume and free peripheral catecholamines in the maintenance of benign essential hypertension. Essential hypertension with low PRA is usually not a hypervolemic state, but it may reflect diminished adrenergic activity, factors associated with aging and effects of a high systemic pressure. High PRA in benign essential hypertension may be at least partly a consequence of hypovolemia resulting from high blood pressure-induced sodium diuresis.

High sodium-low potassium environment and hypertension

The high sodium-low potassium environment of civilized people, operating on a genetic substrate of susceptibility, is the cardinal factor in the genesis and perpetuation of "essential" hypertension. The noxious effects begin in childhood, when habits of excess salt consumption are acquired at the family table, and are perpetuated by continuing habit and by increasing use of convenience and snack foods with artificially high concentrations of sodium and low levels of potassium. Present methods of food preparation leach out the protective potassium. Extradietary sodium chloride is a condiment not a requirement. Some primitive populations clearly preferred potassium chloride to sodium chloride. Chronic expansion of extracellular fluid volume induced by excess salt consumption causes the central and peripheral circulatory regulatory mechanisms to work at cross purposes, resulting in increased arterial pressure. The protective effect of potassium is dramatic and easily demonstrable in animals and man but its mechanism is not known. It cannot be entirely a direct effect on blood pressure because rats protected with extra potassium against a moderately high salt intake live much longer than control rats but have the same elevated blood pressures. In hypertension with a demonstrable "cause," the high sodium-low potassium environment makes a bad matter worse. In nature, feral man and his forebears were not confronted with excessive sodium and deficient potassium; indeed, the reverse was the case. Evolution has provided powerful mechanisms for conserving sodium and eliminating potassium, but no efficient physiologic mechanisms for conserving potassium and eliminating excess sodium. Most laboratory animal "control" diets contain an amount of sodium that fully suppresses aldosterone secretion, and the same is true of the "average" diet of the American people. Inadequate attention to dietary sodium and potassium makes many studies in both animals and man of uncertain validity. Internally, essential hypertension is an exceedingly complex mosaic of physiologic interactions. Viewed from outside, it is a disorder for which genetic material sets the stage; excessive sodium precipitates it and perpetuates it. Extra salt makes all forms more rapidly progressive and accelerates the onset of terminal events; extra potassium is everywhere protective. When an entire population eats excessively of salt, hypertension will develop among those genetically susceptible, but epidemiologic studies of salt versus blood pressure will not show a relation of salt to hypertension. This is the saturation effect. Low sodium diets are therapeutically effective but generally regarded as an impossible or an unnecessary nuisance. Effective prevention programs must be instituted at as early an age as possible. The efficacy of a prophylactic/therapeutic low sodium-high potassium diet should be weighed against the uncertain hazards of a lifetime of pill taking.

Stabilized venous distensibility of normotensive and hypertensive humans on high and low sodium intake

Venous responses to stabilized orthostasis (45 degrees head-up tilt) were studied in seven normotensive subjects and eight hypertensive patients, when on high and low dietary sodium intake. Exchangeable sodium and blood volumes were determined to permit correlation with any significant changes in venous behavior. The intent of this study was to detect and analyze any diet-induced changes in responses of forearm veins to prolonged orthostasis. The pharmacological effects of sodium depletion by medication and diet on arteries and veins of hypertensives are discussed. The results of this study indicate that dietary sodium depletion did not have adverse effects on the ability to maintain stabilized venous tone during orthostasis. These results support recommendations that moderate dietary sodium restriction be included as part of antihypertensive regimens.

Hemodynamic lesions in hypertension

Essential hypertension is increasingly recognized as a nonhomogenous disorder by various methods of study. The hemodynamic approach, coupled with clinical determination of the range and lability of blood pressure, has resulted in the description of several subgroups: labile hypertension with normal or elevated cardiac output, fixed or established hypertension with varying cardiac output and advanced hypertension with normal or low cardiac output. There is a tendency to postulate that these categories are stages of one disorder, but this remains to be proved. Still other patients have been described who may be further set off by exceptionally labile or hyperkinetic features. In some hypertensive patients, the peripheral resistance is normal; however, regardless of its numerical value, it is now considered to be increased if it fails to decrease normally in the presence of elevated cardiac output. Because an elevated cardiac output is the hemodynamic function that differentiates these groups, and renovascular hypertension as well, it is the focus of much current work. New interest in the central blood volume, the peripheral veins, and the portal veins and splanchnic circulation is focused on their connection with cardiac out-put. Newly appreciated, too, is the existence of parasympathetic inhibition in hypertension, which not only contributes to elevations of heart rate, cardiac output and possibly renin secretion, but also depresses baroreflex responses. Thus far, hemodynamic and endocrine mechanisms of hypertension have not been studied together, except possibly through the blood volume, which remains a highly controversial topic. In this paper, some recent work in the above areas is reviewed and emphasis is given to studies in man.