Exogenous Aldosterone Research Articles

Aldosterone Antagonism in Chronic Kidney Disease

Angiotensin-converting enzyme (ACE) inhibitors are potent members of the arsenal to treat chronic kidney disease (CKD). By reducing blood pressure (BP) and disproportionately decreasing intraglomerular pressure, this class of drugs also reduces proteinuria and slows progression of CKD (1,2). Given the high prevalence of cardiovascular disease in this population, it is noteworthy that ACE inhibitors also decrease the incidence of stroke, myocardial infarction (MI), and cardiovascular mortality in patients who are at high cardiovascular risk (3). More recently, data reporting similar benefits of angiotensin receptor blockers (ARB) support their use in the treatment of CKD as well, especially in individuals with type 2 diabetes (4). Furthermore, one sizable study suggested that the combination of an ACE inhibitor and ARB may be more effective than either agent alone (5). Parving and colleagues (6) called attention to the effects of high-dose ARB therapy, up to three times the recommended dose, as an additional means of effectively interrupting the renin-angiotensin-aldosterone system (RAAS). By logical extension, further blockade of the RAAS by direct antagonism of aldosterone also may prove beneficial. Indeed, aldosterone seems to be a potent effector of renal injury (7–9). In the rare cases of primary aldosteronism and its functional analogue, the even more rare Liddle’s syndrome, the observed renal injury probably is independent of the more proximal elements of the RAAS (10,11). Animal models provide an expeditious tool for assessing pathophysiologic change and the efficacy of intervention. The classic model of primary aldosteronism, the mineralocorticoid–nephrectomy–high-salt model of hypertension, develops systemic and glomerular capillary hypertension and sustains renal damage (12). In the remnant kidney model of CKD, ACE inhibitors and ARB attenuate renal injury (13). However, this protection, which is associated with suppression of aldosterone secretion, is abrogated by exogenous aldosterone infusion with return of …

Regulation of maturation and processing of ENaC subunits in the rat kidney

Antibodies directed against subunits of the epithelial Na channel (ENaC) were used together with electrophysiological measurements in the cortical collecting duct to investigate the processing of the proteins in rat kidney with changes in Na or K intake. When animals were maintained on a low-Na diet for 7-9 days, the abundance of two forms of the alpha-subunit, with apparent masses of 85 and 30 kDa, increased. Salt restriction also increased the abundance of the beta-subunit and produced an endoglycosidase H (Endo H)-resistant pool of this subunit. The abundance of the 90-kDa form of the gamma-subunit decreased, whereas that of a 70-kDa form increased and this peptide also exhibited Endo H-resistant glycosylation. These changes in alpha- and gamma-subunits were correlated with increases in Na conductance elicited by a 4-h infusion with aldosterone. Changes in all three subunits were correlated with decreases in Na conductance when Na-deprived animals drank saline for 5 h. We conclude that ENaC subunits are mainly in an immature form in salt-replete rats. With Na depletion, the subunits mature in a process that involves proteolytic cleavage and further glycosylation. Similar changes occurred in alpha- and gamma- but not beta-subunits when animals were treated with exogenous aldosterone, and in beta- and gamma- but not alpha-subunits when animals were fed a high-K diet. Changes in the processing and maturation of the channels occur rapidly enough to be involved in the daily regulation of ENaC activity and Na reabsorption by the kidney.

Aldosterone Promotes Thrombosis Formation After Arterial Injury in Mice

To the Editor: The renin/angiotensin/aldosterone system (RAAS) has been broadly implicated in the pathogenesis of cardiovascular disease.1 Angiotensin converting enzyme (ACE) inhibitors have been shown to be beneficial in reducing cardiovascular events.2 The specific role of aldosterone in promoting ischemic cardiovascular disease is unclear. Recent evidence suggests that subjects with primary aldosteronism are at increased risk of cardiovascular events compared with subjects with essential hypertension,3 suggesting a potential direct role of aldosterone in mediating ischemic events. Human studies have demonstrated that pharmacological blockade of aldosterone with spironolactone in congestive heart failure patients leads to reduced cardiovascular mortality, even in the presence of ACE inhibition.4 Because many cardiovascular events are attributable to thrombosis in the setting of atherosclerosis, we used an animal model to directly determine the effect of elevated aldosterone on atherosclerosis as well as arterial thrombus formation after …

C-Src–Dependent Nongenomic Signaling Responses to Aldosterone Are Increased in Vascular Myocytes From Spontaneously Hypertensive Rats

Aldosterone plays an important role in the pathogenesis of hypertension. We previously demonstrated that nongenomic signaling by aldosterone in vascular smooth muscle cells occurs through c-Src-dependent pathways. Here we tested the hypothesis that upregulation of c-Src by aldosterone plays a role in increased mitogen-activated protein (MAP) kinase activation, [3H]-proline incorporation, and NADPH-driven generation of reactive oxygen species, thereby inducing cell growth, collagen production, and inflammation, respectively, in vascular smooth muscle cells from spontaneously hypertensive rats. The time course of c-Src phosphorylation by aldosterone was shifted to the left in vascular myocytes from hypertensive animals. Aldosterone rapidly increased phosphorylation of p38 MAP kinase and extracellular signal-regulated kinase with significantly greater effects in cells from spontaneously hypertensive rats versus control cells (P<0.05). Aldosterone increased NADPH oxidase activity with significantly greater responses in vascular smooth muscle cells from hypertensive animals (P<0.05). These events were associated with enhanced [3H]proline incorporation (index of collagen synthesis) in cells from spontaneously hypertensive rats (P<0.05). The NADPH oxidase activity increase, collagen synthesis, c-Src, and MAP kinase phosphorylation induced by aldosterone were significantly reduced by eplerenone (selective mineralocorticoid receptor blocker) and PP2 (selective c-Src inhibitor). In conclusion, nongenomic signaling by exogenous aldosterone, mediated through c-Src, is increased in vascular smooth muscle cells from spontaneously hypertensive rats. Upregulation of c-Src signaling may be important in the profibrotic and proinflammatory actions of aldosterone in this genetic model of hypertension.

The effect of tubular epithelial cells activated by aldosterone on renal interstitial fibroblasts in co-culture system

Local aldosterone (ALDO) could be synthesized by human proximal tubular epithelial cell lines (HKC) after the stimulation of endothelin-1 (ET-1) in vitro. T to observe the effect of tubular epithelial cells activated by aldosterone (ALDO) on renal interstitial fibroblasts in co-culture system. (1) Human Proximal tubular epithelial cells of the line HKC were stimulated with ALDO at different concentrations and times, then reverse transcription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) were performed to detect TGF-beta1 expression; (2) HKC were co-stimulated with ET-1 (10(-9) mol/L) and spironolactone at different concentrations and times to evaluate the influence of endogenous ALDO on TGF-beta1 expression; (3) HKC which were activated by 10(-7) mol/L ALDO for 12 h, and hRIFs were co-cultured for 48 h with or without anti-TGF-beta1 antibody (1.0, 2.0 microg/ml) in the media, then the production of type I collagen (Col-I) in the cell layer of hRIFs was detected by ELISA. (1) After stimulation with ALDO, the expression of TGF-beta1 by HKC was up-regulated in a dose-and time-dependent manner. With 10(-9) or 10(-7) mol/L ALDO stimulation (mRNA determination at 12 h and protein at 48 h), the expression of TGF-beta1 was significantly increased (vs 0 mol/L ALDO, P < 0.05 or 0.01). With 10(-7) mol/L ALDO stimulated at different times (mRNA determination at 8 h, 12 h and 16 h and protein at 12 h, 24 h and 48 h), the expression of TGF-beta1 was also significantly increased (vs 0 h, P < 0.05 or 0.01). (2) After co-stimulation with ET-1 and spironolatone, the expression of TGF-beta1 by HKC was down-regulated in a dose-and-time dependent manner along with spironolatone. The expression of TGF-beta1 mRNA and protein was decreased in the 10(-9) or 10(-7) mol/L spironolatone groups compared with 0 mol/L group (P < 0.05 or 0.01). The expression of TGF-beta1 (mRNA and protein) was significantly decreased in 10(-9) mol/L ET-1 and 10(-7) mol/L spironolatone co-stimulation group compared with 10(-9) mol/L ET-1 stimulated group. (3) The production of Col-I by hRIFs which were co-cultured with activated HKC by ALDO, was significantly increased (vs control group in which hRIFs co-cultured with normal HKC, P < 0.01), and this effect was partially inhibited by 1.0 or 2.0 microg/ml anti-TGF-beta1 antibody (P < 0.05). The expression of TGF-beta1 in HKC cells can not only be up-regulated by exogenous ALDO, but also can be up-regulated by endogenous ALDO in an autocrine manner. The HKC cells activated by ALDO can promote the synthesis of Col-I in hRIFs by a "cross talking" way, and this effect is partially mediated by TGF-beta1.

Aldosterone signaling modifies capillary formation by human bone marrow endothelial cells

We investigated the regulation of the epithelial sodium channel (ENaC) in human bone marrow endothelial cells (HBMEC) responding to mineralocorticoid hormones and other accessory effectors. The message for both the mineralocorticoid receptor (MCR) and the alpha subunit of ENaC was expressed in HBMEC as predicted bands of 838 and 521 bp, respectively. In Western blots, the MCR of about 107 kDa was localized primarily in the cytoplasmic compartment but migrated to the nucleus when cell cultures were exposed to exogenous aldosterone. On the other hand, the αENaC was revealed as a membrane-bound protein of approximately 82 kDa, whose abundance increased after aldosterone treatment. Confocal microscopy confirmed the presence of both the MCR and ENaC as nucleocytoplasmic and membrane-bound proteins, respectively, and both colocalized with tubulin in situ. On Matrigel, the mineralocorticoid aldosterone, by itself, did not influence capillary formation by HBMEC, but the diuretic amiloride reduced the organization of HBMEC into capillary-like networks; curiously, aldosterone further exacerbated this inhibitory effect of amiloride. On the fibrin matrix, aldosterone had no influence at all on the length of the newly formed capillaries, but the capillary diameter was highly increased over the control. Aldosterone-mediated capillary swelling was totally reversed by amiloride, which, by itself, also inhibited capillary elongation by HBMEC. Thus, cell signaling by mineralocorticoid hormones in HBMEC appears to proceed in a manner very similar to that in the epithelial cell, thereby leading to an increase in the endothelial cell volume, which may underline the hypertensive state and which may also modify angiogenesis.

Regulation of collecting duct AQP3 expression: response to mineralocorticoid.

Adrenocortical steroid hormones are importantly involved in the regulation of extracellular fluid volume. The present study was aimed at examining whether aldosterone and/or glucocorticoid regulates the abundance of aquaporin-3 (AQP3), -2, and -1 in rat kidney. In protocol 1, rats were adrenalectomized, followed by aldosterone replacement, dexamethasone replacement, or combined aldosterone and dexamethasone replacement (rats had free access to water but received a fixed amount of food). Protocol 2 was identical to protocol 1, except that all groups received fixed daily food and water intake. In both protocols 1 and 2, aldosterone deficiency was associated with increased fractional Na excretion and severe hyperkalemia. Semiquantitative immunoblotting revealed that aldosterone deficiency was associated with a dramatic downregulation of AQP3 abundance. Consistent with this, immunocytochemistry and immunoelectron microscopy revealed a marked decrease in AQP3 labeling in the basolateral plasma membranes of collecting duct principal cells. In contrast, AQP1 and AQP2 abundance and distribution were unchanged. Glucocorticoid deficiency revealed no changes in AQP3, -2, or -1 abundance. In protocol 3, Na restriction (to increase endogenous aldosterone levels) or exogenous aldosterone infusion in either normal rats or vasopressin-deficient Brattleboro rats was associated with a major increase in AQP3 abundance. In protocol 4, aldosterone levels were clamped by infusion of aldosterone, while Na intake was altered from a low to a high level. Under these circumstances, there were no changes in AQP3 or AQP2 abundance, although the level of the thiazide-sensitive Na-Cl cotransporter was decreased. In conclusion, the results uniformly demonstrate that aldosterone regulates AQP3 abundance independently of Na intake. In contrast, changes in glucocorticoid levels in these models do not influence AQP3 or AQP2 abundance. Therefore, in the collecting duct aldosterone may regulate, at least in part, AQP3 expression in addition to regulating Na and K transport.

Aldosterone mediates the changes in hexose transport induced by low sodium intake in chicken distal intestine.

1. In chickens, low Na+ diets markedly decrease the hexose transport in the rectal segment of the large intestine; transport in the ileum shows a lower, but significant reduction and transport in the jejunum is unaffected. These effects involve both apical (SGLT1) and basolateral (GLUT2) hexose transporters. 2. The role of the renin-angiotensin-aldosterone axis (RAAS) in the epithelial response to Na+ intake was studied in chickens fed high-NaCl (HS) and low-NaCl (LS) diets. The V(max) of alpha-methyl-D-glucoside and D-glucose were determined in vesicles from the brush-border (BBMVs) and basolateral (BLMVs) membranes, respectively. The binding of phlorizin to BBMV and cytochalasin B to BLMV were used as indicators of the abundance of SGLT1 and GLUT2, respectively. 3. In HS-adapted chickens, the serum concentration of aldosterone (means +/- S.E.M.) was 35 +/- 5 pg ml(-1) (n = 6) and that of renin was 20 +/- 2 ng ml(-1) (n = 3). In LS-fed birds, these values were 166 +/- 12 pg ml(-1) (n = 6) and 122 +/- 5 ng ml(-1) (n = 3), respectively. Administration of captopril, the inhibitor of the angiotensin-converting enzyme (ACE), to LS-chickens lowered the aldosterone serum concentration without affecting the renin concentration. Captopril also prevented the reduction of apical and basolateral hexose transport in ileum and rectum characteristic of the intestinal response to LS adaptation. 4. Administration of the aldosterone antagonist spironolactone to LS-adapted chickens did not affect the serum concentrations of aldosterone, but prevented the effects of LS intake on hexose transport in both apical and basolateral membranes. This suggests that the effects of aldosterone are mediated by cytosolic mineralcorticoid receptors. 5. Administration of exogenous aldosterone to HS-fed birds induced hexose transport and binding properties typical of the LS-adapted animals. These findings support the view that aldosterone, besides its primary role in controlling intestinal Na+ absorption, can also modulate the expression of apical and basolateral glucose transporters in the chicken distal intestine.

Role of aldosterone in the remnant kidney model in the rat.

The renin-angiotensin-aldosterone system (RAAS) participates in the injury sustained by the remnant kidney. Our studies assessed the importance of aldosterone in that model and the response of aldosterone to drugs interfering with the RAAS. Initially, four groups of rats were studied: SHAM-operated rats, untreated remnant rats (REM), REM rats treated with losartan and enalapril (REM AIIA), and REM AIIA rats infused with exogenous aldosterone (REM AIIA + ALDO). The last group was maintained with aldosterone levels comparable to those in untreated REM rats by constant infusion of exogenous aldosterone. REM rats had larger adrenal glands and a > 10-fold elevation in plasma aldosterone compared to SHAM. REM AIIA rats demonstrated significant suppression of the hyperaldosteronism as well as marked attenuation of proteinuria, hypertension, and glomerulosclerosis compared to REM. REM AIIA + ALDO rats manifested greater proteinuria, hypertension, and glomerulosclerosis than REM AIIA rats. Indeed, by 4 wk of observation all of these features of the experimental disease were similar in magnitude in REM AIIA + ALDO and untreated REM. In separate REM rats spironolactone administration did not reduce glomerular sclerosis but did transiently reduce proteinuria, lowered arterial pressure, and lessened cardiac hypertrophy. In summary, aldosterone contributes to hypertension and renal injury in the remnant kidney model.

Effects of adding spironolactone to an angiotensin-converting enzyme inhibitor in chronic congestive heart failure secondary to coronary artery disease

In chronic heart failure, a diuretic plus an angiotensin-converting enzyme (ACE) inhibitor only partially suppresses aldosterone despite the fact that aldosterone has many harmful effects independent of angiotensin II. These possible harmful effects of aldosterone are magnesium loss, increased cardiac sympathetic activity, and increased ventricular arrhythmias. We have therefore assessed whether adding the aldosterone antagonist, spironolactone, to a loop diuretic and ACE inhibitor reverses any of these potentially harmful effects of residual aldosterone. In a preliminary animal study, we found that exogenous aldosterone reduced myocardial norepinephrine uptake by 24% in anesthetized rats in vivo. In our main study, 42 patients with New York Heart Association II to III congestive heart failure were randomized to spironolactone (50 to 100 mg/ day, titrated to blood pressure and plasma potassium) or placebo in a double-blind fashion. Our principal finding is that cardiac norepinephrine uptake as assessed by 123I-metaiodobenzylguanidine scintigraphy increased with spironolactone (p < 0.01). Spironolactone also elevated plasma magnesium (p < 0.05), reduced urinary magnesium excretion (p < 0.05), and caused a reduction in ventricular arrhythmias on 24-hour ambulatory electrocardiography (p < 0.05). Spironolactone increased plasma renin activity, plasma aldosterone (p < 0.01), 24-hour urinary sodium excretion (p < 0.05), and urinary sodium/potassium ratio (p < 0.01). Echocardiographic-determined measurements of left ventricular systolic and diastolic function were unaltered by spironolactone. Therefore, spironolactone has potentially beneficial effects on cardiac adrenergic tone, divalent cation balance, and ventricular arrhythmias in patients with chronic heart failure who are already receiving standard doses of ACE inhibitors. All of these factors could be significant in the prevention of sudden cardiac death in this population.

Metoclopramide stimulates kaliuresis during felodipine without affecting its natriuresis.

Calcium entry blockers such as felodipine induce natriuresis without a parallel rise of potassium excretion. Previous studies with exogenous aldosterone and felodipine have suggested that the absence of kaliuresis might be explained by a felodipine-induced inhibition of aldosterone release. The natriuresis with calcium entry blockers could not be attributed to a similar mechanism but might be due to the stimulation of intrarenal natriuretic systems such as the dopaminergic system. We studied whether the aselective dopamine antagonist metoclopramide prevents the natriuresis with low and therapeutic felodipine doses and whether metoclopramide-induced aldosterone release promotes kaliuresis with felodipine. Twelve healthy male volunteers participated in a randomized, placebo-controlled, crossover study comparing felodipine infusion during metoclopramide with felodipine alone. Metoclopramide had no significant influence on the pronounced and dose-dependent increases of renal plasma flow and urinary sodium excretion with felodipine. Metoclopramide increased plasma aldosterone concentration from 0.17 +/- 0.03 to 0.60 +/- 0.14 nmol/L, and subsequent felodipine infusion clearly increased urinary potassium excretion by 23 +/- 6 and 35 +/- 8 mumol/min (low and therapeutic doses, respectively). In contrast, potassium excretion remained stable with felodipine alone (+5 +/- 4 and +7 +/- 5 mumol/min, respectively). In conclusion, the natriuretic action of calcium entry blockers cannot be blocked by the aselective dopamine antagonist metoclopramide. This natriuresis is accompanied by kaliuresis only in the presence of elevated endogenous aldosterone concentrations. The ability of calcium entry blockers to prevent a rise of plasma aldosterone thus seems essential for the prevention of urinary potassium losses.

Regulation of the Na-K pump of the rat cortical collecting tubule by aldosterone.

Activities of Na channels and Na pumps were studied in the rat cortical collecting tubule (CCT) during manipulation of the animals' mineralocorticoid status in vivo using a low-Na diet, diuretics, or administration of exogenous aldosterone. Tubules were isolated and split open to expose the luminal membrane surface. Using the whole-cell patch-clamp technique, activities of the apical Na channels and the basolateral Na pumps were measured in principal cells as the currents inhibited by amiloride (10 microM) and ouabain (1 mM), respectively. Na channel current (INa) was not measurable in CCTs from control animals on a normal diet. INa was approximately 200 pA/cell in CCTs from animals on a low-Na diet or infused with aldosterone using osmotic minipumps. Currents attributable to the Na pump (Ipump) were similar in control animals and animals on a low-Na diet. Maximal currents were approximately 35 pA/cell in both groups, and decreased with hyperpolarization of the cell membrane. In contrast, administration of exogenous aldosterone increased Ipump fourfold. Coinfusion of aldosterone and amiloride in vivo through the minipumps did not affect the induction of INa but reduced the induction of Ipump by 80%. We conclude that the induction of channel activity in this tissue is a direct action of aldosterone, whereas the induction of pump activity may be a consequence of the increased Na traffic through the epithelial cells.

Aldosterone mediates an increase in [ 3H]ouabain binding at Na +, K + -ATPase sites in the mammalian inner ear

Na+,K(+)-ATPase has been implicated in the maintenance of high [K+], low [Na+] in endolymph of the inner ear, ionic properties considered to support transduction by the receptor cells. In exocrine ion-transporting epithelia, Na+,K(+)-ATPase activity is modulated by aldosterone, a mineralocorticoid hormone. In the present study, the effect of alteration of serum aldosterone levels on Na+,K(+)-ATPase in ion-transporting regions of the mammalian inner ear was investigated. A high Na+/low K+ diet offered ad libitum for 5 days was utilized to significantly decrease serum aldosterone in male Hartley guinea pigs compared to controls. An injection of aldosterone (10 micrograms/100 g b.wt.) 21 h prior to sacrifice resulted in significant elevation of serum aldosterone over that obtained with the high Na+/low K+ diet. Binding of [3H]ouabain, a specific inhibitor of Na+,K(+)-ATPase, was significantly elevated in microdissected lateral wall of the basal turn of the cochlea and in the ampulla of the semicircular canal, for aldosterone-injected vs. vehicle-injected animals. Serum [Na+] and [Cl-] were elevated in animals on the high Na+/low K+ diet and unaltered by administration of exogenous aldosterone. The enhancement of ouabain binding in inner ear tissues observed in aldosterone-injected animals, therefore, did not appear to reflect an alteration of serum electrolytes per se. The results of these experiments are consistent with the hypothesis that aldosterone increases the number of Na+,K(+)-ATPase sites in ion-transporting epithelia of the mammalian cochlea and semicircular canal.

Discordant aspects of aldosterone resistance in potassium depletion.

Aldosterone resistance, defined as absent kaliuretic response to exogenous hormone, has been described in K depletion. It is not clear whether the absent kaliuresis is due to activation of K-conserving mechanisms or to failure of activation of the Na-K pump in cortical collecting tubules (CCT) by mineralocorticoids. Adrenalectomized male Sprague-Dawley rats were allocated to either a normal or low-K diet. Na-K pump activity (pmol.mm-1.h-1) in microdissected CCT and medullary collecting tubules (MCT, inner stripe of the outer medulla) was determined at 7 or 21 days after allocation to the dietary groups before and after exogenous aldosterone (50 micrograms twice daily, for 3 days). K depletion led to progressive hypertrophic changes in the CCT and MCT manifest in an increase in basal Na-K pump activity. In both K repletion and short-term K depletion (7 days), aldosterone led to the expected increase in CCT Na-K pump activity. With long-term K depletion, the CCT Na-K pump response to aldosterone was blunted. In the MCT where under normal conditions the Na-K pump is aldosterone unresponsive, an increasing aberrant responsiveness to the mineralocorticoid was observed with progressive K depletion. We conclude that apparent aldosterone resistance in short-term K depletion is likely due to activation of K-conserving mechanisms with early preservation of the CCT biochemical response to the hormone. With long-term K depletion, a blunted biochemical response to aldosterone may contribute to the absent kaliuretic response. In the MCT, K depletion led to the development of aberrant responsiveness to aldosterone.

Regulation of amiloride-sensitive Na + absorption in the lizard ( gallotia galloti) colon by aldosterone

1. 1. Acute (AT) or chronic (CT) administration of exogenous aldosterone brought about a considerable increase in transmural potential difference (PD), short-circuit current (Isc) and net sodium flux ( J net Na ). 2. 2. A good relationship between Isc and J m- s Na was observed in CT but not in AT or UC (untreated controls). 3. 3. Addition of mucosal amiloride reduced Isc in AT and CT colons, but did not cause any change in UC colons. The relationship between Isc and J m- s Na , observed in CT was totally suppressed by the diuretic. 4. 4. J net Na was reduced in AT tissues and abolished in CT colons by amiloride. 5. 5. The present results strongly suggest that aldosterone levels quantitatively and qualitatively modify sodium absorption across colonie mucosa in a dose-dependent fashion and that lower levels of the hormone are required to induce the electrogenic Na absorption than to suppress the electroneutral transport.

Renal effects of aldosterone in the sodium bicarbonate infused rat.

The present study investigated the renal function in male Sprague-Dawley rats receiving continuous NaHCO3 (0.077 M) infusion. The renal effects of aldosterone administration in this preparation were also examined. Continuous NaHCO3 infusion significantly (p less than 0.01) depressed plasma aldosterone concentration to 2.36 +/- 1.22 nmol (n = 8) when compared to saline infused rats (4.36 +/- 0.72 nmol, n = 7). The low plasma aldosterone levels in HCO3- infused rats was associated with renal loss of large amounts of K+ and hypokalaemia. Aldosterone administration (42 pmol/min) for 2 h significantly (p less than 0.01) reduced the Na+ excretion rate in bicarbonate infused rats from a mean peak of 9.82 +/- 1.16 to 5.16 +/- 1.20 mumol/min (n = 8). Aldosterone administration did not alter renal excretion in saline-infused rats. It is concluded that NaHCO3 loading depressed endogenous aldosterone secretion, and that this lowered endogenous plasma aldosterone level allows the mineralocortoid effect of exogenous aldosterone to be observed.

Differential up- and down-regulation of Type I and Type II receptors for adrenocorticosteroid hormones in mouse brain

Adult female mice were adrenalectomized and ovariectomized and the concentration of Type I and Type II receptors in whole brain, kidney, and liver cytosol determined at various time thereafter by incubation with [ 3H]aldosterone (+ RU 26988 to prevent binding to Type II receptors) or [ 3H]dexamethasone, respectively. Type I receptor binding in brain was found to undergo a dramatic biphasic up-regulation, with levels six times that of intact levels by 24 h post-surgery and a doubling again by 4–8 days post-surgery. By 16 days, however, Type I specific binding had returned to intact levels. Similar, but less dramatic fluctuations were seen in kidney and liver, whereas much smaller fluctuations were seen fot Type II receptors in all three tissues. In a follow-up study with Scatchard analyses we observed a similar transient up- and down-regulation in maximal binding for Type I, and to a lesser extent Type II receptors in all three tissues. As expected, the apparent binding affinity for both receptors increased after surgical removal of competing endogenous steroids. Radioimmunoassays revealed that plasma concentrations of corticosterone were reduced to near undetectable levels by 24 h post-surgery. A direct comparison of male and female mice revealed no sex-related differences in Type I receptor binding capacity fluctuations in brain cytosol after adrenalectomy-gonadectomy. Lastly, treatment with exogenous aldosterone or corticosterone was found to prevent adrenalectomy-gonadectomy-induced up-regulation of Type I and, to a lesser extent, Type II receptors in brain. Somewhat surprisingly, the potency of these two adrenocorticosteroids appeared to be very similar for both receptor types.

Water and electrolyte transport by the avian ceca.

In galliform birds with well developed ceca, these are functionally important components of the lower intestinal complex, which is capable as a whole of substantial, hormone-regulated homeostatic modification of mixed urine and intestinal luminal fluid before final excretion. Active Na+ transport drives Na-linked absorption of water and Cl- and secretion of K+; there are also lesser Na-independent components of the latter fluxes. These transport processes are appropriately enhanced by dehydration, Na depletion, or exogenous aldosterone.

Urinary excretion of aldosterone metabolite Kelly-M1 in patients with adrenal dysfunction

Using tetrahydroaldosterone antibody a radioimmunoassay was developed to measure substance Kelly-M1 (K-M1) in human urine. The normal values were lower than observed by Kelly et al. who discovered the catabolite after giving large doses of exogenous aldosterone. While in essential hypertension the excretion of K-M1 was predominantly within the normal range, elevated values were found in most cases of 21-hydroxylase deficiency, both the simple virilizing and salt losing form, primary aldosteronism, renal hypertension and cystinosis. Our findings suggest that K-M1 may be formed from 21-deoxyaldosterone and/or by microbial intervention from aldosterone or its metabolites.

Decreased diuretic response to furosemide in rats with acute hepatic failure.

Furosemide diuresis is occasionally reduced in cirrhotic patients with ascites. To define this phenomenon, the amounts of water, electrolytes, and furosemide excreted in urine were measured in control and CCl4-induced acute hepatic failure (AHF) rats. The diuretic action of furosemide (10 mg/kg, i.v.) was reduced in AHF rats, accompanied by increased plasma aldosterone concentration and accelerated urinary K+ excretion rate. Furosemide transiently increased the urinary inulin excretion rate (UVIN) in both control and AHF rats. Then the UVIN quickly returned to the baseline value in control rats, but rapidly dropped below the baseline in AHF rats. To clarify the contribution of aldosterone in these phenomena, AHF rats was adrenalectomized (ADX) and treated with or without exogenous aldosterone. The UVIN in ADX rats given no infusion or a low-dose aldosterone infusion was similar in pattern to that of the control group, but the UVIN in the ADX rats given a high-dose aldosterone infusion showed a pattern similar to that of the AHF rats not adrenalectomized. These findings indicate that an increase in plasma aldosterone concentration is an important factor responsible for the decreased diuretic action of furosemide, along with the reduced glomerular filtration rate.