Plasma levels of atrial natriuretic peptide in man in primary aldosteronism, in Gordon's syndrome and in Bartter's syndrome

Primary Aldosteronism: Changing Definitions and New Concepts of Physiology and Pathophysiology Both Inside and Outside the Kidney

In the 60 years that have passed since the discovery of the mineralocorticoid hormone aldosterone, much has been learned about its synthesis (both adrenal and extra-adrenal), regulation (by renin-angiotensin II, potassium, adrenocorticotrophin, and other factors), and effects (on both epithelial and nonepithelial tissues). Once thought to be rare, primary aldosteronism (PA, in which aldosterone secretion by the adrenal is excessive and autonomous of its principal regulator, angiotensin II) is now known to be the most common specifically treatable and potentially curable form of hypertension, with most patients lacking the clinical feature of hypokalemia, the presence of which was previously considered to be necessary to warrant further efforts towards confirming a diagnosis of PA. This, and the appreciation that aldosterone excess leads to adverse cardiovascular, renal, central nervous, and psychological effects, that are at least partly independent of its effects on blood pressure, have had a profound influence on raising clinical and research interest in PA. Such research on patients with PA has, in turn, furthered knowledge regarding aldosterone synthesis, regulation, and effects. This review summarizes current progress in our understanding of the physiology of aldosterone, and towards defining the causes (including genetic bases), epidemiology, outcomes, and clinical approaches to diagnostic workup (including screening, diagnostic confirmation, and subtype differentiation) and treatment of PA.

Familial or genetic primary aldosteronism and Gordon syndrome

Salt-sensitive forms of hypertension have received considerable renewed attention in recent years. This article focuses on 2 main forms of salt-sensitive hypertension (familial or genetic primary aldosteronism [PA] and Gordon syndrome) and the current state of knowledge regarding their genetic bases. The glucocorticoid-remediable form of familial PA (familial hyperaldosteronism type I) is dealt with only briefly because it is covered in depth elsewhere.

Determinants of natriuretic peptide gene expression

The cardiac natriuretic peptides (NP) atrial natriuretic factor or peptide (ANF or ANP) and brain natriuretic peptide (BNP) are polypeptide hormones synthesized, stored and secreted mainly by cardiac muscle cells (cardiocytes) of the atria of the heart. Both ANF and BNP are co-stored in storage granules referred to as specific atrial granules. The biological properties of NP include modulation of intrinsic renal mechanisms, the sympathetic nervous system, the rennin-angiotensin-aldosterone system (RAAS) and other determinants, of fluid volume, vascular tone and renal function. Studies on the control of baseline and stimulated ANF synthesis and secretion indicate at least two types of regulated secretory processes in atrial cardiocytes: one is stretch-stimulated and pertussis toxin (PTX) sensitive and the other is Gq-mediated and is PTX insensitive. Baseline ANF secretion is also PTX insensitive. In vivo, it is conceivable that the first process mediates stimulated ANF secretion brought about by changes in central venous return and subsequent atrial muscle stretch as observed in acute extracellular fluid volume expansion. The second type of stimulation is brought about by sustained hemodynamic and neuroendocrine stimuli such as those observed in congestive heart failure.

Atrial natriuretic factor significantly contributes to the mineralocorticoid escape phenomenon. Evidence for a guanylate cyclase-mediated pathway

The mechanism underlying the mineralocorticoid escape phenomenon remains unknown. To assess the possible contribution of natriuretic peptides to mineralocorticoid escape, rats were injected with 5 mg deoxycorticosterone acetate for 3 d. Plasma atrial natriuretic factor (ANF) rose to twice basal levels and atrial ANF content decreased significantly by 24 h of treatment. This coincided with renal escape and with a significant increase in urinary cGMP excretion. Plasma ANF remained elevated and atrial ANF content continued to decline by 48 and 72 h while atrial ANF mRNA levels increased significantly only at 72 h. Plasma brain natriuretic peptide did not increase during escape although atrial brain natriuretic peptide mRNA levels increased significantly. Chronically administered HS-142-1 (HS), a specific antagonist of the guanylate cyclase-coupled natriuretic peptide receptors, significantly and dose-dependently impaired the escape phenomenon. The highest dose of HS completely suppressed the increase in urinary cGMP. Despite the continued suppression, partial escape was observed by the end of the observation period. HS alone influenced neither plasma nor tissue or urine parameters. These findings show that despite activation of atrial ANF, blockade of the guanylate cyclase-coupled natriuretic peptide receptors impairs the ability of the kidney to escape the Na+ retaining effect of excess mineralocorticoid in a dose-dependent fashion. Later-acting, unknown mechanisms eventually come into play to mediate the escape phenomenon through a guanylate cyclase-independent pathway. Therefore, ANF of cardiac origin appears to be a major factor initiating mineralocorticoid escape through a guanylate cyclase-dependent pathway.

Ageing and blood pressure regulation: dose-response relationships for angiotensin, blood pressure, atrial natriuretic peptide and aldosterone in normal subjects of varying ages

1. Infusion of increasing doses of angiotensin II (AII) in normal subjects sequentially increased blood pressure, aldosterone and atrial natriuretic peptide (ANP) levels. 2. The slope of ANP response to AII was positively correlated with basal ANP and with the slope of blood pressure response to AII (pressor slope) but not with age. 3. This is consistent with the response of ANP to AII being mediated partly by the rise in blood pressure, independent of ageing. 4. As expected in a selected normotensive population, there was no correlation between basal blood pressure and age, but pressor slope was positively correlated with age. 5. Thus, dose-response relationships may be an index of age-induced alterations in pressure regulatory mechanisms.

Vasoactive peptides in Bartter's syndrome

Patients with Bartter's syndrome exhibit an increased vascular resistance to the pressor effects of angiotensin II and noradrenaline. Further, an increased production of vasodilating renal prostaglandins, perhaps mediating the vascular unresponsiveness, has been hypothesized in this syndrome based on high urinary prostaglandins. To determine whether different peptides might contribute to blood pressure control in this syndrome, the basal immunoreactive plasma levels of an array of vasoactive peptides and catecholamines were analysed in six patients with Bartter's syndrome. Among the vasoconstrictors analyzed, the mean plasma levels of noradrenaline (NA), adrenaline (A) and neuropeptide Y-like immunoreactivity (NPY-LI) were significantly increased as compared to healthy subjects (P = 0.030, 0.046 and 0.001, respectively). The plasma level of the vasodilator substance P (SP-LI) was also higher in these patients (P = 0.057). These results indicate that in Bartter's syndrome the vasoconstrictive effect of catecholamines and angiotensin II may be enhanced by concomitant NPY release. Whether a release of the vasodilator substance P is an independent mechanism or represents a reflex response to the increased secretion of angiotensin II, catecholamines and/or NPY remains to be established. However, the significance of these biochemical findings for blood pressure maintenance in Bartter's syndrome remains to be settled.

Elevation of plasma atrial natriuretic peptide occurs during adrenaline infusion in hypertensive but not normotensive subjects

The levels of plasma atrial natriuretic peptide in response to graded adrenaline infusion were determined in six patients with essential hypertension and six healthy normotensive subjects (controls). Basal plasma adrenaline concentration was similar in both groups and rose progressively and to a similar level during adrenaline infusion. Plasma noradrenaline rose in both groups and to the same extent during the 26 and 39 ng/kg/min adrenaline infusion rates. Basal plasma atrial natriuretic peptide levels were higher in the hypertensives than in the controls. Graded adrenaline infusion had no effect on atrial natriuretic peptide levels in the controls but significantly raised atrial natriuretic peptide levels in the hypertensives. Systolic blood pressure rose progressively during adrenaline infusion at a lower infusion rate in the hypertensives than in the controls. Similarly, while heart rate rose during adrenaline infusion in both groups, there was a greater rise in the hypertensives. The increased cardiovascular responsiveness to adrenaline infusion in patients with essential hypertension may explain why plasma atrial natriuretic peptide levels rose only in this group and not the normotensive subjects.

Subpressor calcium infusion increases isovolumic left ventricular relaxation time and atrial natriuretic peptide in humans

1. Subpressor calcium infusion for 1 h, which raised calcium levels to the upper limit of normal in normal subjects, increased plasma and urinary levels of atrial natriuretic peptide (ANP). 2. Heart rate fell, presumably due to carotid baroreflex stimulation (supported by the fall in noradrenaline) and the resultant fall in cardiac output prevented the expected rise in blood pressure due to the rise in total peripheral resistance (TPR). Thus the increase in ANP was not explained by an increase in blood pressure or noradrenaline. 3. There was no evidence for increased atrial stretch (no increase in atrial area or early velocity of left ventricular filling) as a mechanism for increased ANP. 4. Isovolumic left ventricular relaxation time increased, early velocity of ventricular filling decreased and TPR increased, consistent with increased tone in left ventricular and arteriolar muscle. 5. This suggests a direct effect of calcium on the atrial myocyte, stimulating ANP either through contractile or secretory mechanisms.

Normal renal sensitivity to atrial natriuretic peptide in Gordon's syndrome

To test the hypothesis that renal sensitivity to atrial natriuretic peptide (ANP) is impaired in Gordon's syndrome (hypertension and hyperkalaemia with normal glomerular filtration rate) we infused alpha-hANP into two patients with this syndrome (a sister and a brother, 19 and 18 years of age). For comparison, 11 healthy volunteers were also examined. The infusion of alpha-hANP increased urinary volume and excretion of sodium similarly in the patients and controls. The excretion of potassium did not change in either the patients or the controls. The infusion of alpha-hANP had no effect on the serum potassium levels or the plasma CO2 content in the patients. The present results do not confirm the hypothesis of lack of sensitivity to ANP as a pathophysiological concept in Gordon's syndrome.

The effect of indomethacin on basal and saline-stimulated plasma atrial natriuretic factor levels in normal man

Surprisingly inappropriately high levels of plasma atrial natriuretic factor (ANF) in subjects with Bartter's syndrome are lowered by indomethacin therapy. Indomethacin in normal man causes sodium retention. One might therefore expect plasma ANF to increase in subjects taking indomethacin as a secondary phenomenon. On the other hand a decrease of plasma ANF in normal man similar to that reported in Bartter's subjects may explain the sodium retention caused by the drug in normals. We have studied plasma ANF before and during a two litre, four hour normal saline infusion in eight healthy male subjects both before and following five days of oral indomethacin. Plasma ANF basally was 4.2 +/- 0.9 pmol/l (mean +/- SEM) on no drug and 5.2 +/- 0.6 pmol/l on indomethacin (NS). It increased in response to saline in both studies (7.8 +/- 1.5 pmol/l after two litres of saline on control day; 10.6 +/- 1.5 pmol/l on the drug at the equivalent time, both p less than 0.05 vs basal value). Overall response to saline as assessed by the area under the curve above the basal value of hourly measurements, was not different in the two studies. Basal serum aldosterone and plasma renin activity were reduced by indomethacin. Urinary sodium excretion was not different between groups during the 12 hours before, four hours during and eight hours after the infusion. We have shown that indomethacin does not alter basal or saline stimulated plasma ANF in normal man, a finding in contrast to that reported in subjects with Bartter's syndrome. The sodium retention caused by indomethacin in normal man is not therefore due to a decrease of plasma ANF.

Biochemical correction in the syndrome of hypertension and hyperkalaemia by severe dietary salt restriction suggests renin-aldosterone suppression critical in pathophysiology

1. Plasma potassium and chloride concentrations were raised and plasma renin activity, aldosterone, bicarbonate and arterial pH were reduced in two brothers with the syndrome of hypertension and hyperkalaemia with normal glomerular filtration rate (Gordon's syndrome), on unrestricted or moderately restricted sodium diets. 2. These abnormalities were corrected in both patients within 10 days of severe sodium restriction. 3. Pressor sensitivity to cold and angiotensin II decreased on low sodium diet, associated with a fall in blood pressure. 4. Increasing distal tubular sodium delivery by infusion of normal saline increased fractional excretion of potassium when aldosterone had been stimulated by severely restricted sodium diet, but not when aldosterone levels were low on unrestricted sodium diet. 5. These findings are consistent with excessive sodium reabsorption as the primary renal lesion in Gordon's syndrome, leading to volume expansion and suppression of renin and aldosterone. Severe dietary sodium restriction leading to volume contraction, by stimulating renin and aldosterone and promoting kaliuresis, corrects the abnormalities.

[Atrial natriuretic peptide and its significance for arterial hypertension]

Atrial natriuretic peptide is a recently discovered cardiac hormone with natriuretic, vasodilatory and hypotensive activities. The role of this hormone in the pathophysiology of hypertension is of particular interest. In contrast to an earlier concept, a deficiency of the atrial peptide could not be found in animal models of hypertension or in patients. ANP plasma levels were elevated in SHR with accelerated hypertension, in salt-sensitive Dahl rats, in rats with DOCA-salt-hypertension and in animals with renovascular hypertension. Elevated ANP levels under these conditions can be explained by an expansion of the intravascular volume or by an elevated atrial wall stretch induced by the hypertension itself. In patients with primary hypertension, plasma levels of the peptide are raised in some patients and are normal in others. Plasma ANP levels correlate with age, blood pressure and signs of left ventricular hypertrophy. A negative correlation is described between ANP and renin. Measurement of plasma ANP levels does not allow a differentiation between primary and secondary forms of hypertension. Elevated ANP levels are also found in primary hyperaldosteronism and in renal failure. Stimulation of ANP secretion by physical exercise and dietary salt loading is maintained in hypertension. Infusion of 1-28-hANP leads to a reduction in systemic arterial pressure in normotensives and hypertensives. The natriuresis induced by exogenous ANP is more pronounced in hypertensives. Stimulation of endogenous ANP secretion does not prevent the rise in blood pressure possibly due to a reduction in ANP receptors in target tissues.

Hyperkalemic periodic paralysis in Gordon's syndrome: a possible defect in atrial natriuretic peptide function

We present the case of a 14-year-old boy who had secondary hyperkalemic periodic paralysis caused by Gordon's syndrome. This syndrome consists of hypertension, tubular acidosis, and hyperkalemia with normal glomerular filtration rate. The pathophysiological mechanism is still unknown. Pathophysiological studies suggest that in this disorder the kidney lacks sensitivity to atrial natriuretic peptide. After treatment with hydrochlorothiazide, serum potassium and plasma aldosterone values, plasma renin activity, and blood pressure became normal and the attacks of periodic paralysis disappeared.

Levels of atrial natriuretic peptide are not always consistent with atrial pressure: is there alternative regulation as evidenced in Gordon's and Bartter's syndromes?

1. In Bartter's syndrome, atrial pressures were low, consistent with volume contraction, while atrial natriuretic peptide (ANP) levels were unexpectedly elevated. Infusion of normal saline increased both right atrial pressure (RAP) and ANP levels, while administration of prostaglandin inhibitors raised RAP, probably due to volume expansion, but ANP levels fell paradoxically. 2. In Gordon's syndrome, atrial pressures were unexpectedly low or normal despite volume expansion, while ANP levels were normal. Pressor infusions of angiotensin II either raised right and left atrial pressures (LAP) without increasing ANP, or increased ANP without increasing atrial pressures. 3. In these two syndromes, atrial pressures and ANP levels were poorly correlated, leading to the proposal that other regulators of ANP may be important.

"Chloride-shunt" syndrome: an overlooked cause of renal hypercalciuria

The case of a 7-year-old boy with the normotensive form of "chloride-shunt" syndrome is described. An unusual feature was the clinical presentation with lithiasis, caused by marked hypercalciuria of renal origin. The present studies were carried out to investigate the nature of the renal tubular defect. Indices for proximal and distal sodium chloride reabsorption were increased during hypotonic saline diuresis. Baseline sodium chloride excretion was low but increased above the range of control values after acute furosemide administration. Baseline potassium excretion was low, was not modified by the infusion of sodium chloride and increased significantly during infusions of sodium sulphate or sodium bicarbonate. Calcium excretion remained unchanged during sodium chloride, sodium sulphate or sodium bicarbonate infusions, but increased after furosemide administration. Nasal insufflation of 1-desamino-8-D-arginine-vasopressin induced both an increase in potassium excretion and a decrease in calcium and magnesium excretion. Plasma atrial natriuretic peptide was increased and was not significantly modified by infusion of hypertonic saline or acute administration of furosemide. These findings indicate that the primary renal abnormality appears to be an enhanced tubular reabsorption of sodium chloride, apparently present in the proximal tubule and the ascending loop of Henle. The associated presence of hypercalciuria also suggests a transport defect in the distal tubule. Decreased potassium excretion probably depends on a voltage-shunting defect in the cortical collecting tubule, which can be reversed by increasing the delivery of non-reabsorbable anions or by enhancing the conductance of the luminal membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of altitude on atrial natriuretic peptide: the Bicentennial Mount Everest Expedition

1. Overnight recumbent atrial natriuretic peptide levels were significantly elevated in all ten subjects of the Australian Bicentennial Mount Everest Expedition during the first week at 5400 m, during acclimatization. 2. Twenty-four hour urine volume and urine sodium increased markedly at altitude. 3. Plasma renin activity and plasma aldosterone levels decreased significantly at altitude. 4. No significant changes in plasma cortisol, plasma sodium or potassium, body temperature, systolic or diastolic blood pressure or heart rate were observed. 5. Although it was impossible to control or measure salt and water intake during the study, results suggest that atrial natriuretic peptide may be important in the reduction in renin and aldosterone levels and in the diuresis and natriuresis necessary to adapt to hypoxia at altitude.

Unexpected incidence of low blood pressure 2 years after unilateral adrenalectomy for primary aldosteronism

1. Serial observations of blood pressure after unilateral adrenalectomy for aldosterone-producing adenoma revealed an incidence of hypotension (systolic BP less than fifth percentile for age- and sex-matched normal population) of 27% at 2 years, more than 5 times that predicted. 2. Serial observations of volume regulatory hormones showed significantly raised mean levels of plasma renin activity consistent with hypovolaemia. Significantly reduced mean aldosterone levels despite significantly raised mean plasma renin activity levels may reflect reduced responsiveness of the remaining adrenal. 3. Reduction of significantly elevated preoperative ANP levels to significantly reduced levels postoperatively is also in keeping with postoperative hypovolaemia. 4. A 50% reduction in plasma adrenaline after unilateral adrenalectomy might contribute to reduced noradrenergic activity (prejunctional beta-receptor) and reduced blood pressure, but plasma noradrenaline did not fall significantly postoperatively. 5. Postoperative levels of renin, aldosterone, adrenaline and noradrenaline were not significantly different between those who did, and those who did not, become hypotensive.

Raised plasma levels of atrial natriuretic peptides in Addison's disease

Plasma levels of atrial natriuretic peptides (ANP) were significantly higher in 7 patients with treated Addison's disease (15.8 +/- 8.8 pg/ml, mean +/- SD) than in 7 control subjects (6.1 +/- 3.8 pg/ml) matched for sex, age, body weight and blood pressure. All subjects were studied on their usual sodium intake and had similar urinary sodium excretions. These findings indicate inappropriately high levels of plasma ANP in patients with treated Addison's disease and are possibly due to the lack of adrenal control on ANP synthesis and/or secretion in these patients.

Lack of aldosterone inhibition by atrial natriuretic factor in primary aldosteronism: in vitro studies

Several studies demonstrated that aldosterone secretion, by bovine, rat and human glomerulosa cells, is inhibited in vitro by atrial natriuretic factor (ANF). This effect has also been investigated with conflicting results in cells taken from aldosterone-producing tumors. In the present study, atrial natriuretic factor has been tested on aldosteronoma cells obtained from 4 patients with primary aldosteronism. The cells were studied both with perfusion and incubation systems. Aldosterone secretion was stimulated by ACTH, angiotensin II and potassium with or without ANF 10 microM. In this study ANF lacked to inhibit either basal and stimulated aldosterone secretion, indicating some alterations of ANF-adrenal interaction in this syndrome.

Atrial natriuretic peptide in man

The heart is the major source of atrial natriuretic peptides (ANP). A propeptide is stored in atrial myocytes. In normal humans, atrial distension secondary to volume overload and/or increased atrial pressures are thought to stimulate the secretion of biologically active alpha-ANP (ANF-[99-126], 28 amino residues) into the circulation. Plasma immunoreactive ANP (irANP) rises in response to acute sodium-volume loading, the central shift of volume produced by lying down or by immersion, acute increases in blood pressure (BP), dynamic exercise, or the administration of glucocorticoids or mineralocorticoids. Plasma irANP also rises with aging. Synthetic alpha-ANP infused acutely i.v. can lower BP, reduce plasma volume by an extravascular shift, cause baroreflex-mediated sympathetic activation, directly inhibit adrenal steroidogenesis and lower plasma aldosterone and cortisol, directly inhibit renal renin release, elevate plasma insulin; diuresis, free water clearance and natriuresis increase already in response to low alpha-ANP doses that raise plasma irANP within the physiological-pathological range. It follows that in addition to direct influences on cardiovascular and renal function, the ANP system may comprise a cardio-adrenal feedback mechanism and perhaps also modulate insulin and the release of ADH. The major although yet unproven physiological role of the ANP system may be the protection of the heart against volume and/or pressure overload. The pathophysiological, diagnostic and therapeutic aspects of elevated plasma irANP values, ANP measurements, or administration of synthetic ANP, respectively, in various diseases are currently under intense study and of great potential interest.

Renal tubular hyperkalaemia in childhood

Potassium output from the body is regulated by renal excretion, which takes place predominantly in the late distal and cortical collecting tubules. The accepted model for potassium secretion implies the accumulation of potassium into the cell by the activity of basolateral Na-K-ATPase and its exit through voltage-dependent conductive channels. The factors regulating renal potassium secretion are potassium intake, distal urinary flow, systemic acid-base equilibrium, aldosterone, antidiuretic hormone and, probably, epinephrine. Renal handling of potassium is best studied by the response to the acute administration of furosemide. This loop diuretic not only increases sodium and chloride excretion but also enhances potassium and hydrogen ion excretion and stimulates the renin-aldosterone axis. The term "renal tubular hyperkalaemia" refers to a tubular dysfunction where the hyperkalaemia is disproportionate to any reduction in glomerular filtration rate (GFR) and not due primarily or solely to aldosterone deficiency or to drugs impairing either mineralocorticoid action or tubular transport. The syndromes of renal tubular hyperkalaemia mainly observed in childhood are "chloride shunt" syndrome, hyporeninaemic hypoaldosteronism and primary or secondary pseudohypoaldosteronism. Differential diagnosis between these conditions is easily made if attention is paid to the level of GFR, presence of sodium wasting, activity of the renin-aldosterone axis and renal response to acute administration of furosemide.

Enhanced natriuretic effect of atrial natriuretic factor during mineralocorticoid escape in humans

We examined the question of whether escape from the sodium-retaining effect of mineralocorticoid involves an increased natriuretic effect of atrial natriuretic factor (ANF). Seven healthy volunteers taking a 170 mmol Na/100 mmol K diet received an intravenous bolus (25 micrograms) followed by a 1-hour infusion (0.02 micrograms/kg/min) of ANF (human ANF-[99-126]) before and after 10 days of 9-fludrocortisone acetate, 0.5 mg b.i.d. Escape was accompanied by an increase in body weight (from 72.2 +/- 12.9 to 74.0 +/- 12.6 kg; p less than 0.05), mean arterial pressure (from 95 +/- 4 to 109 +/- 3 mm Hg; p less than 0.01), plasma ANF (from 9 +/- 2 to 24 +/- 4 pmol/L; p less than 0.01), and inulin clearance (from 124 +/- 9 to 137 +/- 7 ml/min; p less than 0.05). Indexes for renal sodium handling (lithium and free water clearance) were compatible with a decreased "proximal" and an increased "distal" tubular reabsorption fraction. ANF infusion raised inulin clearance comparably before and after escape to 138 +/- 10 and 152 +/- 7 ml/min, respectively, but the natriuretic effect was much larger (p less than 0.05) after escape (from 366 +/- 34 to 1294 +/- 278 mumol/min) than before (from 248 +/- 48 to 630 +/- 124 mumol/min). Indexes for tubular reabsorption were consistent with greater suppression of both "proximal" and "distal" tubular sodium reabsorption by ANF after versus before mineralocorticoid expansion. These results indicate that escape is accompanied not only by a rise in plasma ANF but also by potentiation of the natriuretic effect of ANF.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary hyperaldosteronism

Primary hyperaldosteronism is a challenging diagnosis because of its low incidence and variable pathophysiology. Serum potassium, properly done, is the routine screening test, but is not without its limitations. Confirmation of the diagnosis requires demonstration of abnormally high and nonsuppressible values for aldosterone in plasma and urine and low plasma renin activity. Sophisticated biochemical profiling and localization procedures often are required to identify those subtypes that will benefit from surgical management, including aldosterone-producing adenomas, primary adrenal hyperplasia, unilateral hyperplasia, and aldosterone-producing renin responsive adenomas. Glucocorticoid-suppressible hyperaldosteronism and isolated aldosterone-producing adrenal carcinoma are rare additional subtypes to be identified. Differentiation among these subtypes is a developing process that can be expected to continue to improve with new techniques and new understanding of underlying pathophysiology.

Response of atrial natriuretic peptide to adrenaline and noradrenaline infusion in man

1. Atrial natriuretic peptide (ANP) levels were significantly increased during both adrenaline and noradrenaline infusions, in the physiological range, in normal subjects and in patients with essential hypertension. 2. During adrenaline infusion significant increases in both circulating adrenaline and noradrenaline levels were observed. Mean arterial pressure was unaltered. Changes in heart rate were not significant. 3. During noradrenaline infusion, significant increases in circulating noradrenaline and mean arterial pressure were also observed. Heart rate and plasma adrenaline levels were unaltered. 4. Fluctuations in sympathetic nervous system activity may be involved in the regulation of ANP via adrenoceptor stimulated release of ANP. Other known regulators such as atrial stretch and increasing heart rate may modify this response.

Atrial natriuretic factor in human pathophysiology

1. Evidence from numerous experiments incorporating central blood volume expansion and changes in sodium status supports atrial stretch as the prime determinant of ANF release. 2. Plasma ANF levels are the result of both secretion and clearance of the peptide. Clearance is altered by a number of factors, including changes in posture in normal man and is probably impaired in disease states with diminished renal and hepatic blood flow. 3. In normal subjects an inverse relationship exists between plasma ANF values and renin-angiotensin-aldosterone system activity. This relationship is lost and replaced by a positive association in heart failure, presumably reflecting the abnormal concurrence of increased atrial stretch and diminished renal perfusion in this condition. Plasma ANF values rise with increasing severity of heart failure and fall with effective treatment. 4. Plasma ANF values are elevated in hypertension and cardiac tachyarrhythmias possibly reflecting raised central venous and atrial pressures. 5. A variety of other disorders may be associated with abnormal plasma ANF values including cirrhosis and the syndrome of inappropriate ADH secretion. 6. Evidence from low-dose infusions of ANF in normal volunteers suggests that the variations in plasma ANF seen in health and disease are sufficient to exert biological effects. 7. The advent of a specific antagonist is needed to provide further insight into the physiological and pathophysiological roles of ANF.

The syndrome of hypertension and hyperkalaemia with normal glomerular function (Gordon's syndrome). A pathophysiological study

A 14-year-old boy with the syndrome of hypertension and hyperkalaemia with normal glomerular filtration rate (Gordon's syndrome) is described. The patient's clinical symptoms consisted of periodic paralysis, slight metabolic acidosis of the proximal type and hypercalciuria. Prostaglandin excretion was normal. Infusion of atrial natriuretic peptide had no effect on electrolyte excretion or glomerular function although a normal increase in cyclic guanosine monophosphate was demonstrated in plasma and urine. This lack of sensitivity to atrial natriuretic peptide offers a new pathophysiological concept in this syndrome. Treatment with hydrochlorothiazide was successful in this case.

Aldosterone regulation during saline infusion: usefulness of aldosterone/cortisol ratio in the diagnosis of aldosterone-producing adenoma

1. Saline infusion was performed in normal subjects, in essential hypertensives and in patients with aldosterone-producing adenoma (APA), with serial measurements of plasma aldosterone, cortisol and atrial natriuretic peptide (ANP). The effect of recumbency alone was also observed in the normal subjects. 2. Plasma aldosterone after saline infusion was less than 7 ng per 100 ml in the essential hypertensives and normal subjects, but greater than 9 ng per 100 ml in the patients with APA. 3. The aldosterone/cortisol ratio in normal subjects and in essential hypertensives was unchanged or fell during saline infusion, but rose in five of eight patients with APA. 4. Thus, an increase in aldosterone/cortisol ratio after saline infusion appears to be diagnostic of APA, but its absence does not exclude it.

Effects of angiotensin and noradrenaline on atrial natriuretic peptide levels in man

1. A significant positive correlation was found between changes in circulating noradrenaline (NA) levels and changes in atrial natriuretic peptide (ANP) levels during NA infusion and clonidine administration. 2. A significant positive correlation was also found between changes in arterial blood pressure and changes in ANP level during infusion of angiotensin II and of NA. 3. Two patients with very high circulating NA levels due to phaeochromocytoma, but receiving alpha- and beta-blockade, did not have clearly elevated ANP. A third not receiving medications and aged 73 years had elevated levels. 4. Atrial natriuretic peptide response to NA and angiotensin II may be mediated by changes in blood pressure levels or increased noradrenergic and angiotensinergic receptor activity in the atria or both. Atrial natriuretic peptide may have a role in blood pressure regulation in both normotensive and hypertensive man.

Alpha-h-ANP injection in normals, low renin hypertension and primary aldosteronism

Atrial natriuretic peptide, a hormone secreted by the heart, is involved in salt and fluid homeostasis and also exerts an inhibitory effect on aldosterone production in vitro. In order to elucidate if this effect is also present in man, 6 normal volunteers, 5 low renin hypertensive patients (LRH) and 7 patients with primary aldosteronism (PA) have received 100 micrograms of alpha-h-Anp as bolus i.v. (The decrease in blood pressure was mild and transient in all groups, whereas a marked diuretic effect was observed in all hypertensives even in PA where high levels of endogenous ANP have been found. In normals we observed a significant decrease of plasma aldosterone values while in PA and LRH this effect was not evident. This phenomenon associated with a greater natriuretic effect in LRH and PA, as compared with normals, demonstrates the lack of the correlation between ANP-induced diuresis and aldosterone inhibiting properties.

Effect of alpha-human atrial natriuretic peptide in low renin essential hypertension and primary aldosteronism

Atrial natriuretic peptide (ANP), besides its diuretic and antihypertensive effects, exhibits an "in vitro" inhibitory action on aldosterone. In order to elucidate if these effects are present also "in vivo", we injected 100 micrograms of alpha-human ANP as a bolus in normal volunteers, low renin essential hypertensive subjects (LRH) and in patients with primary aldosteronism (PA). A transient hypotensive effect was seen in all patients, without significant variations of heart rate. The diuretic and saluretic effects of ANP were greater in hypertensive subjects, even in PA where endogenous ANP levels are known to be elevated. Plasma aldosterone values decreased significantly only in normal volunteers. In conclusion, in LRH and PA renal effects of ANP are not diminished, although its aldosterone-inhibiting properties are less evident than in normals.

The syndrome of hypertension and hyperkalaemia with normal GFR. A unique pathophysiological mechanism for hypertension?

Based on 28 reported patients, constant features of the syndrome of hypertension and hyperkalaemia are hyperkalaemia, hyperchloraemia, normal renal glomerular function and, in all adult patients, hypertension. Inconstant features include short stature, intellectual impairment and muscle weakness. Levels of renin and aldosterone are low, but respond to dietary salt restriction and diuretic therapy, both of which reverse the hypertension and hyperkalaemia. The basic abnormality is excessive renal sodium retention, leading to chronic suppression of renin and aldosterone; the latter is then hyporesponsive to the hyperkalaemic stimulus. Dietary salt loading or impaired production of any natriuretic or chloriuretic factor (for example atrial natriuretic peptide or renal natriuretic prostaglandins) would predispose to development of the syndrome. With normal GFR, this appears to be a unique mechanism for hypertension and hyperkalaemia.