METABOLISM OF ALDOSTERONE IN SEVERAL EXPERIMENTAL SITUATIONS WITH ALTERED ALDOSTERONE SECRETION

Plasma aldosterone levels are elevated in patients with pulmonary arterial hypertension in the absence of left ventricular heart failure: a pilot study

AIMS

Elevated levels of the mineralocorticoid hormone aldosterone are recognized as a modifiable contributor to the pathophysiology of select cardiovascular diseases due to left heart failure. In pulmonary arterial hypertension (PAH), pulmonary vascular remodelling induces right ventricular dysfunction and heart failure in the absence of left ventricular (LV) dysfunction. Hyperaldosteronism has emerged as a promoter of pulmonary vascular disease in experimental animal models of PAH; however, the extent to which hyperaldosteronism is associated with PAH in patients is unknown. Thus, the central aim of the current study is to determine if hyperaldosteronism is an unrecognized component of the PAH clinical syndrome.

METHODS AND RESULTS

Plasma aldosterone levels and invasive cardiopulmonary haemodynamic measurements were obtained for 25 patients referred for evaluation of unexplained dyspnoea or pulmonary hypertension. Compared with controls (n = 5), patients with PAH (n = 18) demonstrated significantly increased plasma aldosterone levels (1200.4 ± 423.9 vs. 5959.1 ± 2817.9 pg/mL, P < 0.02), mean pulmonary artery pressure (21.4 ± 5.0 vs. 45.5 ± 10.4 mmHg, P < 0.002), and pulmonary vascular resistance (PVR) (1.41 ± 0.6 vs. 7.3 ± 3.8 Wood units, P < 0.003) without differences in LV ejection fraction or pulmonary capillary wedge pressure between groups. Among patients not prescribed PAH-specific pharmacotherapy prior to cardiac catheterization, a subgroup of the cohort with severe pulmonary hypertension, aldosterone levels correlated positively with PVR (r = 0.72, P < 0.02) and transpulmonary gradient (r = 0.69, P < 0.02), but correlated inversely with cardiac output (r = -0.79, P < 0.005).

CONCLUSIONS

These data demonstrate a novel cardiopulmonary haemodynamic profile associated with hyperaldosteronism in patients: diminished cardiac output due to pulmonary vascular disease in the absence of LV heart failure.

Plasma volume in cirrhosis of the liver: its relation of portal hypertension, ascites, and renal failure

Plasma volume was measured by using albumin-(131)I- and (51)Cr-labeled erythrocytes in 24 control subjects, 140 patients with hepatic cirrhosis, and 10 patients with various portal-systemic shunts for the relief of noncirrhotic portal hypertension. The cirrhotic patients included subgroups with ascites, functional renal failure, and portacaval anastomoses. Elevated values for plasma volume, by both methods, were found in each group of patients.The lymph space drained by the thoracic duct was measured by a radioisotopic technique in six patients with cirrhosis and ascites. The amount of radioactivity in this space was found to be negligible in accounting for the elevated plasma volume. Similar results were obtained when the degree of leakage of albumin-(131)I into the ascites was determined in 10 patients with cirrhosis.The plasma volume was unusually elevated in patients who had bled from esophageal varices, and paired comparisons before and after portacaval shunt normal values. There was a statistically significant correlation between normal values. There was a statistically significant correlation between plasma volume and wedged hepatic venous pressure measured in 36 patients.We concluded that the elevated values for plasma volume in cirrhosis are valid and are not artifacts due to leakage of albumin-(131)I from the circulation during mixing. We also concluded that portal hypertension is responsible for the plasma volume expansion; however, we were unable on this basis to explain the failure of portacaval shunting to return the plasma volume to normal, unless the shunt or some other factor keeps the plasma volume elevated.

Aldosterone metabolism in the isolated perfused liver of R and S hypertension-prone Dahl rats

The effect of a chronic oral salt load on hepatic metabolism of aldosterone was examined in isolated livers of salt-resistant (R) and salt-sensitive (S) hypertension-prone male Dahl rats perfused with d-[4-14C]aldosterone (10(-9) M). Aldosterone was analyzed by radioimmunoassay and [4-14C]aldosterone radiometabolites by high-performance liquid chromatography. In salt-loaded S rats, systolic blood pressure was 30 mmHg higher than in the other three groups (P less than 0.01). In S rats, on standard and high-salt diets, plasma renin activity was 64% (P less than 0.001) and 50% (P less than 0.01) lower, and, on the standard diet, plasma aldosterone was 50% (P less than 0.01) lower than in R rats. Salt loading suppressed plasma renin activity by 42% (P less than 0.05) in R rats and plasma aldosterone by 66 and 33% (P less than 0.01) in R and S rats, respectively. In isolated perfused liver, hepatic function did not differ between various groups. Hepatic clearance of aldosterone in R rats given water and saline and in S rats given water did not differ, whereas hepatic clearance of aldosterone was 28 and 35% higher in salt-loaded S rats when compared with S rats on water (P less than 0.01) and with salt-loaded R rats (P less than 0.001), respectively. Polar and reduced metabolites of [4-14C]aldosterone were released into the circulation in livers of R and S rats on both diets, but highest relative levels of polar metabolites of aldosterone were found in salt-loaded S rats. In all groups, only polar metabolites of aldosterone were excreted in bile.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acute stress, (1-24)ACTH administration and changes in superfusion temperature and flow rate on the in vitro secretion of glucocorticosteroids and aldosterone from the Mongolian gerbil (Meriones unguiculatus) adrenal gland

The release of glucocorticosteroids and aldosterone rapidly decreased after start of superfusion and reached a steady base-line within 60-90 min of superfusion. While secretion markedly varied between experiments, it was very constant in the same experiment (coefficient of variation: 7.4-2.2% for glucocorticosteroids and 5.8-3.9% for aldosterone). After repeated exposure of adrenal tissue to 1 IU/ml (1-24)ACTH, glucocorticosteroid release progressively increased; under the same conditions aldosterone secretion was not changed. Glucocorticosteroid secretion from glands of animals stressed by 1-hr confinement or of animals injected with 6 IU (1-24)ACTH was significantly higher than that of controls over the 60-min superfusion period. Aldosterone secretion was not affected significantly by these pretreatments. After reduction of temperature from 35 to 1 degrees C, steroid release ceased. Elevation of temperature from 12 to 32 degrees C resulted in a linear increase of glucocorticosteroid and aldosterone secretion. A highly significant positive correlation was found between glucocorticosteroid and aldosterone amounts secreted from adrenals superfused at temperatures between 1 and 35 degrees C (r = 0.91, n = 116, P less than 0.0001). Changes of flow rate from 0.5 to 1.5 ml/min for 5 min induced a short term (1 min) stimulation of glucocorticosteroid and aldosterone release; reduction of flow rate to 0.5 ml/min for 5 min drastically diminished secretion of steroids below control levels for 1 min.

Influence of sodium balance on ACTH/adrenal corticosteroid dose-response curves in the dog

In order to define short-term ACTH/corticosteroid dose-respone characteristics, we infused ACTH for 1 h at each of five incremental rates into pedigreed male beagle dogs in four different states of sodium balance. Progressive sodium depletion was associated with progressive increased in basal (pre-ACTH) plasma levels of renin, angiotensin II, aldosterone, 18-hydroxycorticosterone (18-OH-B), and 18-hydroxy-11-deoxycorticosterone (18-OH-DOC). Administration of dexamethasone significantly reduced the preinfusion levels of cortisol, aldosterone, 18-OH-B, and 18-OH-DOC. The threshold dose of ACTH required to elicit an aldosterone response during low-sodium intake was similar to that for cortisol, but was higher during normal or high-sodium intake. Steepest portions of the dose-response curves were at lower rates of ACTH infusion for cortisol than for aldosterone, and maximum increment was much greater for cortisol (60-fold) than for aldosterone (12-fold). Whereas the slopes of ACTH/aldosterone and ACTH/18-OH-B dose-response curves were steepened by lower sodium diets, the ACTH/cortisol response was significantly flattened by severe sodium depletion. We conclude that ACTH is a potent and direct-acting short-term regulator of aldosterone secretion, subject to modification by altered sodium balance.

Hormonal responses during treatment of acute diabetic ketoacidosis with constant insulin infusions

Changes in glucagon, growth hormone (GH), cortisol, renin and aldosterone accompanying the metabolic disturbances and dehydration of severe diabetic ketoacidosis were studied over a 24 h period in eight patients treated with a constant intravenous insulin infusion. Mean steady state plasma-free insulin levels achieved were 28.6--49 mu/1 in patients receiving 2 u/h but a satisfactory rate of fall of glucose was not always obtained until the infusion dose was increased to 4 u/h or more. The total insulin dose administered was positively correlated with the level of plasma glucagon and cortisol on admission. During insulin infusion, both glucagon and cortisol fell but the rate of fall was not related to dose or plasma level of free insulin achieved. In six of eight patients studied increments in plasma GH above admission levels were observed during insulin treatment. Admission values of both plasma renin activity and plasma aldosterone were raised. The renin levels were highest in newly diagnosed diabetics, and two patients with long-established diabetes showed only small increments despite profound dehydration. Plasma renin activity, but not plasma aldosterone correlated with the fluid and sodium retention over the initial 24 h treatment period, but not with potassium requirements. The urinary excretion rates of the small molecular weight proteins GH and insulin, were considerably elevated over the treatment and convalescent periods.

Renin-angiotensin-aldosterone system in long-term renal transplant patients

Seventeen anephric patients who constituted the subjects of this study received renal allografts between the years 1969 to 1973. The renin-angiotensin-aldosterone mechanism was evaluated in relation to either a normotensive or hypertensive clinical state in these subjects. Group I (Controls) were normotensive and on a normal diet; Group II were normotensive, on sodium restriction for five days, followed by saline infusion on the seventh day; and Group III were hypertensive, on similar sodium restriction for five days, followed by saline infusion on the seventh day. Glomerular filtration rates and levels of plasma renin and aldosterone, and the secretion rate of the latter were obtained on appropriate days. These studies confirm that an intact renin-angiotensin-aldosterone relationship exists in human renal transplant patients. The presence of high aldosterone secretion rate without hypertension is a new but unexplained finding. The lack of correlation of high aldosterone secretion rates in our normotensive and hypertensive patients suggests that aldosterone does not play a detectable or significant role in the pathogenesis of chronic or sustained transplant hypertension.

Increased plasma aldosterone concentration in response to hemodialysis in nephrectomized man

The nephrectomized patient maintained on intermittent hemodialysis while awaiting renal transplantation provides an excellent model for studying the influence of factors other than the renal renin-angiotensin system that play a role in the regulation of plasma aldosterone concentration. Peripheral plasma aldosterone concentrations were determined using a sensitive radioimmunoassay method in nine anephric patients in the recumbent position immediately before and after hemodialysis. Average patient weight fell 1.5 kg following 12 hours of dialysis on the Kiil dialyzer. Plasma sodium concentration decreased from 137 ± 1 (SE) to 132 ± 1 mEq/liter, plasma potassium concentration decreased from 4.8 ± 0.3 to 3.2 ± 0.1 mEq/liter, and the ratio of sodium to potassium increased from 31.3 ± 1.9 to 41.7 ± 0.9. Plasma aldosterone concentration increased from 9.7 ± 1.6 ng/100 ml plasma before dialysis to 17.9 ± 2.1 ng/100 ml plasma after dialysis despite the lack of kidneys to produce renin. Plasma cortisol concentration did not change significantly (17.5 ± 2.0 µg/100 ml plasma to 14.8 ± 1.9 µg/100 ml plasma). These results show that plasma aldosterone concentration increased in anephric patients in response to hemodialysis. This increase occurred without a concomitant increase in plasma cortisol levels, suggesting absence of an adrenocorticotropic hormone response, and was independent of the renal reninangiotensin system.

Hepatic clearance of renin in canine experimental models for low- and high-output heart failure

Hepatic blood flow, hepatic extraction of renin, and hepatic clearance of renin were compared in normal conscious dogs, in dogs with constriction of the thoracic inferior vena cava (as a model of low-output heart failure), and in dogs with an aortic-caval fistula (high-output heart failure). Both "failure" preparations showed marked sodium retention. Renin was measured by methods described previously and expressed as nanograms of angiotensin produced during incubation per milliliter of plasma. Hepatic plasma flow was determined by the sodium sulfobromophthalein method. The dogs with low-output heart failure had a marked reduction in hepatic plasma flow, while those with high-output failure showed no significant change in this flow. Plasma renin was significantly elevated in both models of heart failure. Dogs with low-output failure had an increase ( P < .05) in hepatic renin extraction from a normal value of 19.8% to 33.4%, while those with high-output failure showed a decrease in hepatic renin extraction to 11.9% ( P < .01). The hepatic clearance of renin in low-output failure (104 ml/ min) was the same as the average normal value of 104 ml/min, while clearance of renin by the liver in high-output failure was reduced to 51 ml/min ( P < .001). The data provide evidence that the decreased metabolism of renin contributes substantially to the increased plasma level of renin in experimental high-output heart failure.

Plasma renin in chronic experimental heart failure and during renal sodium "escape" from mineralocorticoids

A striking increase in the plasma renin level occurred in dogs with low output right heart failure secondary to tricuspid insufficiency and pulmonic stenosis and in three of five animals with high output failure produced by a large arteriovenous fistula. When dogs with a small arteriovenous fistula were given daily injections of DOCA, the renal sodium "escape" phenomenon occurred. In these animals, the level of plasma renin was suppressed during DOCA administration both during the initial period of sodium retention and also later when sodium balance was normal or negative. In contrast, when dogs with a larger arteriovenous fistula but without evidence of cardiac failure were given DOCA, they retained sodium and developed signs of congestive heart failure. However, in these animals with congestion and ascites, in contrast to the dogs that developed spontaneous high output failure, the plasma renin was low. Renin-substrate was unaltered in all of the experimental situations studied except for the decrease observed in dogs with low output right heart failure. In these animals, it seems likely that decreased renin-substrate was secondary to hepatic congestion and liver damage. The renin-angiotensin system does not seem to be related to the "escape" phenomenon, and renin does not appear to be the factor that makes the kidney unusually responsive to mineralocorticoids. Thus, in experimental heart failure the renin-angiotensin system was activated, but in the congestive syndrome produced by DOCA the plasma renin level was suppressed.

Hemorrhage in normal man: effect on renin, cortisol, aldosterone, and urine composition

Images