Effects of corticosteroids on urinary ammonium excretion in humans

This study was designed to examine the selective effects of glucocorticoid and mineralocorticoid classes of steroid hormones on urinary ammonium excretion in humans. In 22 10-day studies, normal male volunteers received either 9 alpha-fludrohydrocortisone or hydrocortisone, alone or with the receptor antagonist spironolactone or mifepristone. The small but significant increase in ammonium excretion noted with the administration of 9 alpha-fludrohydrocortisone was associated with a significant decrease in serum potassium. In contrast, a significantly larger increase in ammonium excretion was noted with hydrocortisone, without concomitant electrolyte changes. Spironolactone did not alter the effect on ammonium excretion by either corticosteroid, whereas mifepristone markedly blunted the hydrocortisone-induced increase in urinary ammonium excretion. It was concluded that glucocorticoids increase urinary ammonium excretion in humans and that this effect occurs through binding to the Type II (glucocorticoid) receptor rather than by cross-occupancy of the Type I (mineralocorticoid) receptor.

Effects of fludrocortisone on sympathetic nerve activity in humans

Fludrocortisone reduces plasma norepinephrine in healthy humans, but forearm vascular and pressor responses to norepinephrine are potentiated. The effects of fludrocortisone on sympathetic nerve activity in healthy humans are not known. To investigate these effects we evaluated muscle sympathetic nerve activity, heart rate, and arterial pressure in 11 healthy volunteers during three protocols: (1) before and on day 7 of fludrocortisone (0.4 mg/d) treatment with ad libitum diet (n = 6); (2) before and on day 7 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 7); and (3) before and on day 2 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 4). Placebo did not alter any parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of fludrocortisone acetate and deoxycorticosterone acetate on salt appetite in mice

Three genotypes of mice were shown to increase their intake of 3% sodium chloride (NaCl) following administration of fludrocortisone acetate (25 mg/kg), a synthetic steroid having strong mineralocorticoid/glucocorticoid activity. However, treatment with deoxycorticosterone acetate (DOCA) (10 mg/kg), a corticosteroid with predominantly mineralocorticoid activity, did not increase 3% NaCl consumption by the stock tested. In contrast, both fludrocortisone and DOCA have been shown to be effective activators of sodium appetite in rats. The essential importance of glucocorticoids in potentiating mineralocorticoid activation of sodium hunger in mice is suggested.

Benefits of fludrocortisone in the treatment of symptomatic vasodepressor carotid sinus syndrome

OBJECTIVE

To assess treatment with fludrocortisone in vasodepressor carotid sinus syndrome.

PATIENTS AND METHODS

Eleven patients, mean (SD) age 83 (5) years, with daily dizzy episodes and a median of five (range two to 20) syncopal episodes over a median of one year were studied. All had vasodepressor carotid sinus syndrome (> 50 mm Hg fall in systolic blood pressure during carotid sinus massage independent of bradycardia). Carotid sinus massage was carried out while the patient was supine and upright (tilt table) before and after 600 micrograms intravenous atropine. Phasic heart rate and blood pressure recordings were monitored throughout. The study was repeated after 100 micrograms of fludrocortisone daily by mouth for two weeks. Patients continued to take fludrocortisone for a six month follow up period.

RESULTS

Baseline systolic blood pressure was (mean (SD)) 169 (31) mm Hg and the RR interval was 770 (150) ms. After carotid sinus massage, systolic blood pressure fell to 113 (27) mm Hg (p < 0.01) and RR was 1060 (210) ms (NS). The vasodepressor response was 56 (12) mm Hg. Baseline systolic blood pressure after two weeks of fludrocortisone treatment was 171 (37) mm Hg (NS); but the fall in systolic blood pressure during carotid sinus massage was significantly reduced (32 (14) mm Hg; p < 0.01). At six months follow up, two patients complained of intermittent dizziness and no patients had syncope.

CONCLUSION

Fludrocortisone effectively reduces the vasodepressor response and relieves the symptoms of vasodepressor carotid sinus syndrome.

Kaliuretic response to aldosterone: influence of the content of potassium in the diet

The excretion of potassium (K+) decreased by 50% (30 v 63 mEq/d, P < .01) when subjects consumed a diet that was low in K+ for 3 days. Although part of this conservation of K+ was achieved in part by suppressing the release of aldosterone, nevertheless providing exogenous mineralocorticoids did not lead to a large kaliuresis when there was a modest degree of K+ depletion. Accordingly, the purpose of this study was to evaluate possible mechanisms for this antikaliuretic response to mineralocorticoids. The renal handling of K+ was examined by independent analysis of the two factors that influence its excretion, the driving force to secrete K+ and the urine volume. This driving force is reflected in a noninvasive fashion by the transtubular [K+] gradient (TTKG). Stimuli to increase the rate of excretion of K+ in subjects on a normal and a low-K+ diet included the administration of 200 micrograms fludrocortisone (9 alpha F), the induction of a high urine flow rate (9 alpha F+furosemide), the induction of bicarbonaturia (9 alpha F+acetazolamide), and the excretion of Cl(-)-poor urine (< 15 mEq/L). On the low-K+ diet, the peak value for the TTKG 3 to 4 hours after 9 alpha F was less than half that while on the normal diet (6.4 v 14, P < 0.01). In contrast, the TTKG was not significantly different on either diet when there was bicarbonaturia or the excretion of a Cl(-)-poor urine (18 v 17 and 17 v 16, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Glycyrrhizin induces mineralocorticoid activity through alterations in cortisol metabolism in the human kidney

It has been suggested that the mineralocorticoid action of glycyrrhizin is caused by a defect in the conversion of cortisol to cortisone through inhibition of the enzyme 11 beta-dehydrogenase (11 beta-DH). We investigated the functional significance of the inhibition of this enzyme as a mechanism of the mineralocorticoid action of glycyrrhizin. Eighteen healthy volunteers were divided into three groups of six and treated as follows: (1) 225 mg glycyrrhizin/day, (2) 0.1 mg 9 alpha-fluorocortisol (FC)/day and (3) 225 mg glycyrrhizin and 1.5 mg dexamethasone/day, all of which were given for 7 days. The administration of glycyrrhizin or FC induced a similar mineralocorticoid effect; specifically, suppression of plasma renin activity, hypokalaemia and kaliuresis. During the concomitant administration of glycyrrhizin and dexamethasone, however, these mineralocorticoid effects were significantly attenuated. During the administration of glycyrrhizin, urinary excretion of cortisol increased without change in the plasma levels of cortisol, while both plasma level and urinary excretion of cortisone decreased. Changes in cortisol metabolism were not observed during the administration of FC. These results demonstrated the functional significance of the inhibition of 11 beta-DH in the mineralocorticoid activity of glycyrrhizin in man.

Mineralocorticoid escape in patients with compensated cirrhosis and portal hypertension

Failure to escape from mineralocorticoids in compensated cirrhosis is considered a major argument supporting the overflow theory of ascites. To assess the frequency and mechanism of mineralocorticoid escape in cirrhosis, 9-alpha-fluorohydrocortisone (0.6 mg/day) was administered to 19 patients with compensated cirrhosis, portal hypertension, and no history of ascites who were able to maintain sodium balance on a 250 mmol Na+ diet. Fifteen patients (78.9%) escaped from mineralocorticoids, while 4 patients (21.1%) did not escape and developed ascites. Patients who did not escape had significantly higher cardiac index (4.97 +/- 0.42 vs 3.46 +/- 0.21 L.min-1.m-2) and lower peripheral vascular resistance (485.9 +/- 37.5 vs. 665.8 +/- 32.9 dyne.s.cm-5/m2) than those who escaped. Hepatic venous pressure gradient was not significantly different. The escape phenomenon was associated with a significant increase in mean arterial pressure, creatinine clearance, and atrial natriuretic factor and suppression of plasma renin activity. All of these parameters showed minimal or no changes in patients who did not escape. These results indicate that failure to escape from mineralocorticoids is uncommon in patients with compensated cirrhosis, is related to an inadequate expansion of effective plasma volume due to the accumulation of ascites, and occurs in patients with marked peripheral arteriolar vasodilation.

Renal response to atrial natriuretic peptide in nonedematous sodium-retaining dogs

ANP administered to cirrhotic dogs or chronic caval dogs with ascites and urinary sodium retention (USR) usually causes heterogeneity of natriuretic response. To assess whether this same phenomenon would occur in the absence of edema, ANP at 100 ng/kg/min was given to dogs before and after the induction of USR by a variety of techniques. Eight dogs were over-diuresed with furosemide over a 2-day period, and 9 dogs were subjected to subacute hemorrhage over a similar period. These dogs were retested with ANP one day later. All 8 dogs given furosemide showed no response to ANP (delta UNa V = 7.4 +/- 4.8 microEq/min), compared to a normal response prior to the diuretic (delta UNa V = 128 +/- 34 microEq/min). The 9 hemorrhaged dogs also responded normally to ANP prior to this manipulation (delta UNa V = 74 +/- 14 microEq/min), but a blunted response post-hemorrhage (delta UNa V = 35 +/- 13 microEq/min). This profile was made up of 5 dogs who responded to ANP (delta UNaV = 62 microEq/min) and 4 who had no response whatsoever (delta UNa V = 3 microEq/min). When 8 dogs were given USR because of continuous mineralocorticoid administration, none responded, but all had a magnified natriuretic response to ANP during the 'escape' phase. Eight dogs were administered minoxidil (10 mg) by mouth daily to induce USR. All 8 dogs responded to ANP (delta UNa V = 93 +/- 6 microEq/min) which was no different from the pretreatment response (delta UNa V = 65 +/- 3 microEq/min).(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of 9-alpha-fluorhydrocortisone (Florinef) in extrarenal regulation of potassium]

There are evidences that adrenal hormones regulate extrarenal potassium homeostasis. The present study evaluated the effect of Florinef modulation on extrarenal mechanisms in potassium adaptation of adrenalectomized rats. The results demonstrated that the rats treated with Florinef had serum potassium levels at normal range probably due to an increase in cellular potassium uptake consequently to en enhanced activity of Na-K-ATPase.

Drug effects on orthostatic intolerance induced by bedrest

Effective and practical preventive procedures for postflight orthostatic intolerance are highly desirable. The current practice of attempts to expand plasma volume by ingestion of salt and fluids before reentry has proven benefits. This study evaluated alternative options using fludrocortisone (F) to expand plasma volume (PV), dextroamphetamine (Dex) to enhance norepinephrine (NE) release and atropine (A) to reduce the effects of vagal stimulation. Seven subjects with proven post-bedrest orthostatic intolerance returned for a 7-day 6 degrees head-down bedrest study. F (0.2 mg) was given at 8:00 AM and 8:00 PM the day before and 8:00 AM the day the subjects got out of bed (2 hours before standing). PV was measured before and 1 hour after the last dose of F. D (5 mg) and A (0.8 mg) were then taken orally 1 hour before the stand test. F expanded PV by 16% and caused sodium retention. Four of the 7 subjects stood for 1 hour post-bedrest and HR, plasma NE and PRA responses to standing were greatly enhanced and sustained. Although there was a narrowing of pulse pressure, the ability to overcome orthostatic intolerance with these countermeasures was largely due to vasoconstriction and sustained high heart rate. The existing literature on pharmacologic countermeasures for post-flight and post-bedrest orthostatic hypotension is reviewed, and the results are discussed in that context.

Modulation of the secretion of potassium by accompanying anions in humans

In animals, secretion of potassium (K) in the cortical collecting duct (CCD) is modulated by the properties of the accompanying anion. In humans, results are inconclusive as previous studies have not differentiated between a kaliuresis due to a rise in the concentration of K from one due to an increase in the volume of urine. Our purpose was to study the effects of chloride (Cl) and bicarbonate on the secretion of K in the CCD in humans using the transtubular K concentration gradient (TTKG), a semi-quantitative index of secretion of K in the terminal CCD. After control blood and urine samples were obtained, all subjects ingested 0.2 mg fludrocortisone to ensure that mineralocorticoids were not limiting the secretion of K. The anionic composition of the urine was varied using three protocols: Normal subjects (N = 11) ingested cystine and methionine to induce sulfaturia; nine subjects with a contracted ECF volume (to lower the concentration of Cl in the urine) were also studied during sulfaturia following the ingestion of cystine and methionine; 13 normovolemic subjects were studied during bicarbonaturia following the ingestion of acetazolamide. When the concentration of Cl in the urine was greater than 15 mmol/liter, sulfate had no effect on the TTKG. With lower concentrations of Cl in the urine, the TTKG rose 1.5-fold. The TTKG rose 1.8-fold in the presence of bicarbonaturia despite concentrations of Cl in the urine that were greater than 15 mmol/liter, suggesting that bicarbonate has additional effects on this K secretory process. At comparable concentrations of sulfate and bicarbonate in the urine, the TTKG was increased only with bicarbonaturia.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that high dose cortisol-induced Na+ retention in man is not mediated by the mineralocorticoid receptor

We have previously shown that high dose cortisol (F; 240 mg/day)-induced Na+ retention and systolic blood pressure (BP) increases are not inhibited by the glucocorticoid (type II) receptor antagonist RU486. Adequacy of type II receptor blockade with RU486 was clearly demonstrated, indicating that the Na+ retention was not mediated through the glucocorticoid receptor. Spironolactone (Sp: 400 mg/day), in a preliminary assessment, also did not inhibit F-induced Na+ retention. The purpose of this study was to determine whether the Na+ retention produced by F administration is mediated by the type I receptor by comparing the effects of F to a potent type I agonist [9 alpha-fludrohydrocortisone (9 alpha FF)] with and without Sp administration. The effects of the two agonists and Sp on urinary K excretion and BP were also compared. Normal male volunteers, on a constant daily diet for 10 days, received either F (240 mg/day) or 9 alpha FF (3.0 mg/day) with or without Sp (400 mg/day) for the last 5 days. The mean cumulative reductions in Na+ excretion during the 5 days compared to baseline values before hormone administration were 255 +/- 38 and 494 +/- 81 mmol/5 days for F (n = 9) and 9 alpha FF (n = 5), respectively (P = 0.01). Sp (n = 5) completely inhibited 9 alpha FF-induced Na+ retention (494 +/- 81 vs. -37 +/- 130 mmol/5 days; P less than 0.01), but had no effect (n = 5) on F-induced Na+ retention (255 +/- 38 vs. 193 +/- 50 mmol/5 days; P = NS). After the expected first day kaliuresis, the effects of both steroids on net cumulative urinary K+ excretion were minimal. Systolic BP was increased by F, but not 9 alpha FF, and Sp did not inhibit this increase. A 2-fold greater Sp-inhibitable Na(+)-retaining effect of the mineralocorticoid demonstrates that the failure of Sp to block F-induced Na+ retention is not due to inadequate type I receptor blockade. Based on these findings and earlier studies, we conclude that high dose (stress level) F-induced Na+ retention and systolic BP increase are not mediated by either the mineralo- or glucocorticoid receptor in normal man.

The transtubular potassium concentration in patients with hypokalemia and hyperkalemia

It is advantageous to make an independent assessment of the potassium (K) secretory process and the luminal flow rate in the renal cortex to evaluate K handling by the kidney during hypokalemia or hyperkalemia. The transtubular potassium concentration gradient (TTKG) is a semiquantitative index of the activity of the K secretory process. The purpose of this study was to define expected values for the TTKG in normal subjects with hypokalemia or following an acute K load. During hypokalemia of non-renal origin, the TTKG was 0.9 +/- 0.2; in contrast, the TTKG was significantly higher during the hypokalemia of hyperaldosteronism, 6.7 +/- 1.3. The TTKG was 11.8 +/- 3.6, 2 hours after normokalemic subjects received 0.2 mg 9 alpha-fludrocortisone (9 alpha-F). To obtain expected values during hyperkalemia, normal subjects ingested 50 mmol potassium chloride; 2 hours later, the TTKG was 13.1 +/- 3.8. Therefore, the expected value for the TTKG must be interpreted relative to the concentration of K in the plasma. Circumstances were also defined where the TTKG is low despite hyperaldosteronism, namely, during a water diuresis and pre-existing hypokalemia.

Some aldosterone-producing adrenal tumours also secrete cortisol, but present clinically as primary aldosteronism

1. Two patients with angiotensin-responsive aldosterone-producing adenoma (APA) and one with adrenal cortical carcinoma demonstrated autonomous secretion of cortisol as well as of aldosterone. 2. The response of cortisol and of aldosterone to ACTH did not differentiate between the two APA which secreted cortisol and the eight which demonstrated normal suppression with dexamethasone. 3. Concurrent autonomous secretion of cortisol as well as aldosterone may occur in patients who present clinically with primary aldosteronism. 4. Biochemical distinctions between adenomas may reflect differences in their cellular composition.

Effect of converting enzyme inhibition on renin synthesis and secretion in mice

We have investigated the relative importance of renal renin stores and de novo synthesis during stimulation of renin secretion and the role of transcription and posttranscriptional factors in providing increased synthesis of renin. When enalapril was administered to previously untreated mice, plasma renin concentration increased 40-fold within 1.5 hours, and remained at a high level for the 8 days of the experiment. Renal renin decreased by 82% after 24 hours and thereafter increased to levels higher than controls. Calculations of renin turnover, based on data for the rate of metabolism of renin in plasma, indicated that most of the renin released in the first 24 hours could be accounted for by the decrease in renal renin stores, indicating that de novo synthesis played only a minor role. After 24 hours, however, when both plasma renin concentration and renal renin increased, the calculated rate of renin synthesis increased to nearly 40 times the rate in controls. When enalapril was administered to mice that had been depleted of plasma and renal renin by chronic sodium loading, plasma renin concentration increased markedly within 1.5 hours, but to only half the level achieved in the previously untreated mice. No decrease in renal renin occurred, suggesting that the renal renin remaining after chronic sodium loading was not available for release. Renal renin messenger RNA increased 4.5-fold after 6 hours, and after 8 days had increased to 5.0 times the level at day 0. The increase in calculated rate of renin synthesis was maximal between 5 and 8 days, when it was 54 times greater than at day 0. During enalapril treatment, there were marked increases in the granulation of the juxtaglomerular cells and in the amount of rough endoplasmic reticulum and Golgi apparatus they contained. These results suggest that posttranscriptional factors play a major role in determining the rate of renin synthesis.

Effect of mineralocorticoids and salt loading on renin release, renal renin content and renal renin mRNA in mice

1. DOCA and 9 alpha-fludrocortisone were given to mice on a high-sodium diet for periods of up to 20 weeks, resulting in decreases in plasma renin concentration, renal renin concentration and renal renin mRNA with both treatments. 2. Plasma renin concentration was suppressed prior to suppression of renin mRNA and renal renin levels, indicating that suppression of synthesis and secretion of renin occur separately. 3. The decrease in renal renin concentration that occurred with DOCA was greater and more rapid than the decrease that occurred with 9 alpha-fludrocortisone, suggesting that DOCA caused intra-renal breakdown of renin. 4. When DOCA was given to mice on a low-sodium diet, plasma renin concentration and renal renin concentration increased, indicating that the effects of DOCA on renin levels were dependent on dietary sodium. 5. Renin secretion and synthesis appeared to be controlled by different mechanisms and sodium balance has an important effect on both processes.

Antialdosterones: incidence and prevention of sexual side effects

The use of spironolactone in the treatment of hypertension has been limited by the occurrence of sexual side effects, mainly menstrual disturbances in women and gynaecomastia in men. In order to minimize this limitation on the use of an effective potassium-sparing antihypertensive agent, two strategies can be proposed: (1) A decrease in the daily dose of spironolactone. In 182 patients with essential hypertension treated with spironolactone alone for a mean follow-up period of 23 months, daily doses of 75-100 mg were as effective on blood pressure as doses of 150-300 mg. In contrast, the development of gynaecomastia--91 cases among 699 men--was dose-related in 6.9% (50 mg/day) to 52.2% (150 mg or more/day) of the cases. (2) An improvement in the receptor-binding specificity of spironolactone. Three 9 alpha, 11 alpha-epoxy derivatives have been characterized in vitro in rats and in rabbits. They exhibited a 3- to 10-fold decrease of the antiandrogenic and progestagenic effect, compared with spironolactone. In humans, one of these derivatives counteracted the fall in urinary Na/K ratio induced by 9 alpha-fluorohydrocortisone at a 25 mg dose.

Mineralocorticoid activity and the excretion of an oral potassium load in normal man

In six healthy males on a fixed sodium/potassium (Na/K) intake, we studied the relation between plasma K and urine K and Na excretion after an oral K load. Studies were repeated during fludrocortisone (0.5 mg bid) or spironolactone (50 mg qid), that is, after escape from the Na-retaining and Na-excreting effects of these drugs. A steep positive relation between plasma K (ordinate) and urine K or Na (abscissa) was found, compatible with a strong influence of changes in plasma K on K and Na excretion. Fludrocortisone reset the relation to a lower level of plasma K. Spironolactone, on the other hand, had little effect on these relations, although a tendency towards a higher plasma K could be recognized. Paradoxically, the K load was excreted less efficiently during fludrocortisone, probably due to enhanced cellular K deposition. Prolonged kaliuresis relative to the transient rise in plasma K and natriuresis was found only without medication. Only in this situation aldosterone rose and fell parallel to plasma K. We conclude that: 1) chronic mineralocorticoid increase shifts the set point of both K and Na excretion following a K load to a lower plasma K, compatible with resetting of the positive influence of plasma K on distal solute delivery towards a lower plasma K; 2) total kaliuresis is paradoxically low due to enhanced cellular K uptake; 3) blockade of endogenous aldosterone action has relatively little influence on these relations between plasma K and urine K or Na; 4) the contribution of acute aldosterone stimulation to the excretion of a single oral K load can be recognized as a delayed kaliuresis extending beyond the peak in plasma K.

Glucocorticoid and mineralocorticoid stimulation of atrial natriuretic peptide release in man

To investigate the influence of a mineralocorticoid and a glucocorticoid on plasma immunoreactive atrial natriuretic peptide (irANP) and possible functional correlates, eight normal men received in random order 9 alpha-fludrocortisone acetate (9 alpha F; 0.6 mg/day), prednisone (50 mg/day), and placebo each for 9 days. Their diet contained 130 mmol sodium and 75 mmol potassium daily. The mean supine plasma irANP levels were similar on days 2, 4, and 9 of placebo treatment [25 +/- 10 (+/- SE), 27 +/- 5, and 27 +/- 6 pmol/L, respectively]. Mean plasma irANP levels were 76 +/- 42 (P less than 0.05), 89 +/- 34, and 93 +/- 29 pmol/L (P less than 0.01), respectively, on days 2, 4, and 9 during 9 alpha F administration, and 68 +/- 37 (P less than 0.05), 83 +/- 41, and 48 +/- 18 pmol/L on the same days during prednisone administration. Compared with the placebo period, sodium intake minus urinary output during 9 alpha F administration averaged +41 mmol at the time of blood sampling on day 2, +112 mmol on day 4, and +149 mmol on day 9; body weight was unchanged on day 2 and increased by 0.7 and 1.1 kg on days 4 and 9, respectively. Escape from 9 alpha F-induced renal sodium retention occurred on days 5 and 6. During prednisone administration, sodium intake minus urinary output and body weight did not change. Plasma volume and BP rose significantly during 9 alpha F (P less than 0.05) but not during prednisone administration. Plasma renin, aldosterone, and norepinephrine (NE) decreased during 9 alpha F treatment (P less than 0.05 to less than 0.01); during prednisone treatment, plasma aldosterone levels were lower on day 9 only. Cardiovascular pressor responsiveness to angiotensin II was enhanced during 9 alpha F but not prednisone administration, while blood pressure reactivity to NE was not significantly modified. These findings demonstrate that 9 alpha F and prednisone in high doses provoke remarkably similar increases in plasma irANP, but that the glucocorticoid-induced rise in plasma irANP is due to a mechanism other than sodium and volume retention.

Renal handling of calcium and phosphate during mineralocorticoid administration in normal subjects

The renal handling of calcium and phosphate in relationship to the renal handling of sodium was studied in 7 healthy male volunteers under steady state metabolic conditions during prolonged (10 days) mineralocorticoid treatment. Calcium excretion was reduced together with sodium excretion during the early phase of mineralocorticoid treatment, whereas it increased independent of sodium excretion following the escape. Phosphate excretion did not change throughout. These results suggest that when there is extracellular volume expansion without increase in sodium intake and/or excretion, there is a dissociation of calcium and sodium excretion, suggesting that extracellular volume can affect the renal tubular handling of calcium probably as a result of mechanism(s) operating in the distal nephron.

Primary role of hyperkalemia in the acidosis of hyporeninemic hypoaldosteronism

A 65-year-old woman with mild renal insufficiency had persistent hyperkalemia and hyperchloremic acidosis. Her plasma aldosterone level was relatively low for her hyperkalemia, and her urine pH was low. Fludrocortisone acetate administration corrected both hyperkalemia and acidosis by increasing urinary excretion of potassium and net acid, implicating deficient mineralocorticoid activity in the distal renal tubule in this patient. During this medication urinary ammonium excretion increased, but urine pH remained low, so that urinary titratable acid excretion did not decrease. On the other hand, correction of hyperkalemia by administration of a potassium-calcium exchange resin alone also resolved the acidosis by increasing urinary ammonium excretion. This increment exceeded the decrement of urinary titratable acid excretion, which was caused by raised urine pH secondary to increased urinary ammonium excretion, and resulted in increase of net acid excretion. Thus, in this patient, hyperkalemia appears to be a decisive causative factor in the acidosis, with deficient mineralocorticoid effect only contributing in part to the reduction of net acid excretion and the acidosis.

Human atrial natriuretic polypeptide during escape from mineralocorticoid excess in man

1. Plasma concentrations of human alpha-atrial natriuretic polypeptide (h-alpha ANP) during escape from the effects of mineralocorticoid excess were determined in six healthy volunteers. 2. Escape, as indicated by an abrupt increase in sodium excretion on the third to sixth day of 9 alpha-fludrocortisone acetate administration (0.6 mg/day), was observed in all subjects. 3. The mean plasma h-alpha ANP level was 30.9 +/- SEM 8.8 pmol/l on the control day; it increased exponentially in response to 9 alpha-fludrocortisone acetate administration, reached a significant level (114.0 +/- 22.4 pmol/l, P less than 0.05) on the day before escape and remained elevated during escape. 4. The 24 h creatinine clearance and blood pressure did not change significantly before the escape. Plasma h-alpha ANP increased markedly when the cumulative sodium balance exceeded 220 mmol. 5. These results suggest that h-alpha ANP may play a contributory role in natriuresis and diuresis after mineralocorticoid excess.

Changes in the plasma levels of atrial natriuretic peptides during mineralocorticoid escape in man

Plasma levels of atrial natriuretic peptide (ANP) were measured by radioimmunoassay in eight normal healthy volunteers before and during mineralocorticoid escape. Mean plasma ANP on a fixed sodium intake before fludrocortisone was 6.5 +/- SEM 1.1 pg/ml. Within 24 h of fludrocortisone administration there was a significant increase in plasma ANP which continued to increase daily reaching a plateau by day 4 (14.9 +/- 2.4 pg/ml) to day 7 (15.1 +/- 2.6 pg/ml). The rise in plasma ANP was closely related to the amount of sodium retained during the fludrocortisone treatment and the sodium 'escape' occurred by days 4 to 7. These results support the concept that ANP could play an important hormonal role in over-coming the sodium-retaining effects of mineralocorticoids in man.

Aldosterone-producing adenomas responsive to angiotensin pose problems in diagnosis

1. A subgroup of patients with aldosterone-producing adenoma (APA) have been identified who lack many of the biochemical features regarded as characteristic of APA and used to distinguish APA from bilateral adrenal hyperplasia. 2. In these patients, aldosterone is responsive to infused angiotensin II (angiotensin-responsive APA), which explains their uncharacteristic responses to upright posture, saline infusion and fludrocortisone acetate administration. 3. The angiotensin-responsiveness of these patients may derive from the contralateral adrenal gland, since renin levels are less completely suppressed in angiotensin-responsive APA than in angiotensin-unresponsive APA. 4. However, while the excretion of 18-oxo-cortisol was consistently increased in angiotensin-unresponsive APA, it was normal in angiotensin-responsive APA, consistent with biochemical and biosynthetic distinctiveness residing in the tumours. 5. Angiotensin-responsive APA should always be considered as an alternative diagnosis to bilateral hyperplasia causing primary aldosteronism.