Hormonal actions of the heart and of lungs on the isolated kidney

Toward a broader understanding of aldosterone in congestive heart failure

Discovered some 50 years ago, aldosterone (ALDO) has come to be recognised as a mineralocorticoid hormone with well-known endocrine properties in epithelial cells that contribute to the pathophysiology of congestive heart failure. This includes Na + resorption at the expense of K+ excretion in classic target tissues: kidneys, colon, sweat and salivary glands. Though less well known, Mg2+ excretion is likewise enhanced by ALDO, while adrenal ALDO secretion is regulated by extracellular Mg2+ ([Mg2+ ]o). An emerging body of information has and continues to identify other endocrine actions of ALDO receptor-ligand binding. They include: promoting an efflux of cytosolic free Mg2+, or [Mg2+]i, in exchange for Na+ in such non-epithelial cells as peripheral blood mononuclear cells; its influence on endothelial cell function; and its central actions that involve regulation of cerebrospinal fluid composition produced by epithelial cells of the choroid plexus, activity of the hypothalamic paraventricular nucleus involved in Na+ appetite, Na+ and H2O excretion and sympathetic nerve activity, and the regulation of TNF-α production from central and/or peripheral sources. Extra-adrenal steroidogenesi and auto/paracrine properties of ALDO generated de novo in the cardiovasculature are now under investigation and preliminary findings suggest they contribute to tissue repair. The past decade has witnessed a revival of interest in this steroid molecule. In years to come, an even broader understanding of ALDO's contribution to the pathophysiology of congestive heart failure will undoubtedly emerge.

Aldosteronism revisited: perspectives on less well-recognized actions of aldosterone

Aldosterone is a mineralocorticoid with protean actions in both epithelial and nonepithelial cells. These include endocrine properties of circulating aldosterone that promote Na(+) resorption at the expense of well-recognized K(+) excretion and less well-recognized Mg(2+) excretion in classic target tissues: kidneys, colon, and sweat and salivary glands. The regulation of adrenal aldosterone secretion by [Mg(2+)](o) is also less well appreciated. More recently recognized endocrine actions of aldosterone include induction of Mg(2+) efflux in exchange for Na(+) in such nonepithelial cells as peripheral-blood mononuclear cells and influence on epithelial cells of the choroid plexus, where aldosterone alters the composition of cerebrospinal fluid that contributes to blood-pressure regulation. An association between primary aldosteronism and idiopathic intracranial hypertension has recently been reported. Extraadrenal steroidogenesis with de novo aldosterone production by the cardiovasculature, where its auto-/paracrine properties may contribute to tissue repair at sites of injury, has been observed. These less well-recognized actions of aldosterone have led to a revival of interest in how this steroid molecule contributes to the pathophysiology of various clinical disorders.

Prevention of aortic and cardiac fibrosis by spironolactone in old normotensive rats

OBJECTIVES

Because the synthesis of aldosterone is mainly modulated by angiotensin II through type I receptor stimulation and because converting enzyme inhibition (CEI) does not modify aortic extracellular matrix in old normotensive rats, the aim of the present study was to determine whether inhibition of aldosterone formation was able to prevent aortic fibrosis in old Sprague-Dawley normotensive rats.

BACKGROUND

We have previously shown that long-term aldosterone antagonism prevents the age-related increase in aortic collagen accumulation in young spontaneously hypertensive rats, independent of blood pressure changes. In contrast, we reported that the positive effects of CEI in the prevention of aortic collagen accumulation were related to the inhibition of angiotensin II actions on angiotensin II type I receptors.

METHODS

For this purpose, we studied the histomorphometric and stiffness (echo-tracking technique) changes of an eight-week treatment with the aldosterone antagonist spironolactone by comparison with placebo.

RESULTS

At the end of treatment, spironolactone in conscious animals did not change intra-arterial blood pressure, aortic and carotid wall thickness, and cardiac weight. Cardiac collagen density and, to a lesser extent, carotid collagen and elastin densities and contents were significantly decreased in association with an increase of carotid distensibility.

CONCLUSIONS

These results show that in old normotensive rats, spironolactone can markedly prevent cardiac and, to a lesser extent, arterial fibrosis and improve arterial stiffness, despite a lack of hypotensive effect.

Prevention of aortic fibrosis by spironolactone in spontaneously hypertensive rats

We have previously shown that long-term angiotensin-converting enzyme (ACE) inhibition prevents the increase in aortic collagen in spontaneously hypertensive rats (SHRs), independent of blood pressure reduction. More recently, we reported that the effects of ACE inhibition in the prevention of aortic collagen accumulation were related to the inhibition of angiotensin II actions on angiotensin II type 1 receptors. Aldosterone, the synthesis of which is mainly modulated by angiotensin II through type 1 receptor stimulation, is known to promote cardiac fibrosis in different experimental models. The aim of the present study was to determine whether inhibition of aldosterone formation was able to prevent aortic fibrosis in SHRs. For this purpose, we compared the effects of a 4-month treatment with the aldosterone antagonist spironolactone with the ACE inhibitor quinapril in 4-week-old SHRs. Control SHRs and Wistar-Kyoto (WKY) rats received placebo for the same period of time. At the end of treatment, in conscious SHRs vs WKY controls, quinapril completely prevented the development of hypertension, whereas spironolactone produced only a slight but significant reduction in blood pressure. Aortic hypertrophy was significantly prevented by ACE inhibition but not by spironolactone. On the contrary, aortic collagen accumulation was completely prevented by both quinapril and spironolactone. In the latter case, collagen density was significantly below that of WKY controls. These results show that in SHRs, spironolactone can markedly prevent aortic fibrosis in the presence of a very slight antihypertensive effect. It is suggested that ACE inhibition or type 1 receptor antagonist-induced prevention of aortic collagen accumulation is at least partially related to aldosterone inhibition.

Some aspects of amoeboid microglia in the corpus callosum and neighbouring regions of neonatal rats

The distribution and form of amoeboid microglia in the brain of neonatal rats have been studied with the light and electron microscope. With the silver carbonate method of Rio-Hortega, two major 'colonies' of amoeboid microglia are identified: (1) in the supraventricular corpus callosum in which the nerve fibres are widely spaced, and (2) at the medial angle of the lateral ventricle inferior to the corpus callosum. Scattered amoeboid cells are also seen in the cavum septum pellucidum and in the lumen of the lateral ventricle. Associated with the subependyma forming the roof of the lateral ventricle there are also numerous amoeboid cells. Ultrastructural studies show that the subependyma includes cellular elements with features intermediate between those of immature subependymal cells and full-blown amoeboid microglia. It is suggested that the latter are derived from the subependymal cells and that, once they are formed, they leave the subependyma and migrate into the corpus callosum and elsewhere. With the metallic stain, the amoeboid microglia present a wide diversity of appearances, some of which bear a close resemblance to typical microglia. It is therefore suggested that amoeboid microglia change into typical microglia. The present study clearly demonstrates that amoeboid microglia are active phagocytes. Their cytoplasm is heavily loaded with secretory granules (lysosomes) and give a positive reaction with PAS and acid phosphatase.

Factors affecting the antidiuretic actions of the 18-monoacetate of (+)-aldosterone and of a substance secreted by eart muscle, in rats

The method for the assay of a steroid-like substance secreted by the heart (HS) in terms of the biological activity of the 18-monoacetate of (+)-aldosterone (18MA) has been improved. Rats were equipped with ascending carotid, descending external jugular and bladder polyethylene cannulae and the urethra was ligated, under pentobarbitone anaesthesia, 24–36 h before use. Assays were made in restrained animals during sustained water diuresis induced by an intravenous infusion of glucose, 5%, and NaCl, 0ṁ9%; 2: 1 at 9 mlh−1. Antidiuretic responses (measured as the area under the curve) to ascending carotid injections of 18MA and of HS, made at 0ṁ01 ml s−1, maximum 15 s, were obtained from single dilutions of HS and 18MA: urine flow per min was recorded from drop (0ṁ025 ml) counters. Denervation of the carotid sinus above the carotid cannula did not influence the antidiureses. Data obtained were analysed by normal statistical procedures. Ascending carotid injections of 18MA and HS did not influence mean systemic arterial pressures, the clearances of creatinine and of PAH or the urinary outputs of Na+ and K+. The antidiuresis produced was compatible with the release of ADH by HS and by 18MA. Marked seasonal variations in threshold sensitivity to 18MA and in the slopes of the log dose-effect curves for the antidiuretic actions of 18MA are described. Variations both in the threshold sensitivity and in the log dose-effect curves for the anti-diuresis caused by 18MA occur between rats of different strains.

The formation of a renally active peptide by cat lungs from gamma-globulin in vitro and the plasma concentrations of this peptide, in vivo

1. A substance (LS), extracted in aqueous acetone and separated by partition and thin-layer chromatography, has been obtained from lung perfusates and from the systemic blood of cats.2. LS is assayed biologically in rats during sustained saline diuresis by measurement of the muequiv Na retained. This parameter is linearly related to the log concentration of LS infused.3. Lungs perfused with Tyrode fluid neither contain nor produce LS. Production of LS begins when gamma-globulins (in cat plasma, mixed ox globulins or equine Cohn II) are present in the perfusing fluid.4. The proteinase inhibitor trasylol does not prevent the formation of LS by lung; trasylol protects LS from break-down during re-perfusion and during isolation from perfusates or from blood.5. In cats under chloralose anaesthesia LS is present during haemorrhage in systemic arterial and mixed venous blood, the arterial concentration of LS is approximately four times the venous.

The isolation of a renally active substance from arterial blood

1. A substance (Art. HS) which resembles the 18-monoacetate of D-aldosterone (18 MA) in its biological actions is found in arterial blood of cats and sheep: Art. HS is assayed in terms of antidiuretic activity equivalent to synthetic 18 MA.2. In cats under chloralose anaesthesia, dialysis of arterial blood (2-3 ml./min) in a small external circuit (8-15 ml.) without disturbance of heart rate, blood pressure or respiration, predicts a physiological concentration of Art. HS equivalent to 31.5-51.9 ng 18 MA/100 ml. Efficiency of dialysis assumed in this calculation is 100%.3. Art. HS is almost evenly distributed throughout the plasma and formed elements of blood.4. Concentrations of Art. HS found during severe arterial haemorrhage are equivalent to 188 +/- 6.7 and 151 +/- 9.2 ng 18 MA/100 ml. in cats and sheep respectively.5. Art. HS has been isolated from 27.6 l. sheep arterial blood by ethyl acetate: chloroform 1:1 extraction, defatting by partitioning between methanol and petroleum ether and purifying by seven-stage thin layer chromatography on MN Kieselgel UV(254). Final yield was equivalent in activity to 21.6 mug 18 MA. Synthetic 18 MA was used as R(F) marker. Spots of 2 mug 18 MA are visible on MN Kieselgel UV under U.V. Art. HS activity equivalent to 21.6 mug 18 MA cannot be seen.6. Art. HS was not detectable in IVC blood of cats under chloralose anaesthesia during haemorrhage. The threshold for detection was the equivalent of 15-20 ng 18 MA/100 ml.7. Art. HS resembles a substance liberated by the heart (Lockett & Retallack, 1970a, b, 1971) in chromatographic properties, biological properties and stability in aqueous solution. Art. HS is very much more stable in aqueous solution than 18 MA.

The separation of renal activity from lung and from the venous effluent from perfused lungs

1. Antidiuretic and salt-retaining activity has been separated from cat and ox lung, and from the venous effluent of blood-perfused cat lungs, by acetone extraction, gel filtration, partition and thin-layer chromatography.2. The chromatographic properties of the renally active substance from lung and from pulmonary venous blood are similar.3. The renal actions of these substances, demonstrable in vivo and in the isolated organ, are characterized by reduction in the excretion of water and Na. Renal blood flow, glomerular filtration rate and the urinary Na/K are not significantly affected.4. Concentrations of the lung substance which equate with angiotensin II-val(5)-amide in reduction of urinary Na in rats during water diuresis and under alcohol sedation do not raise the mean arterial pressure of the anaesthetized rat nor contract the superfused rat colon. At these dose levels angiotensin II is markedly vasopressor and contracts the superfused rat colon.

Factors controlling the secretion of a substance biologically resembling the 18-monoacetate of D-aldosterone by heart muscle

1. Previous work has demonstrated that the cat heart secretes a substance which resembles the 18-monoacetate of D-aldosterone (18 MA) in chromatographic properties and biological actions. This substance (HS) releases ADH from the neurohypophysis and, in higher concentration, causes renal retention of salt and water. HS is extracted from blood, separated chromatographically and assayed in terms of equivalent 18 MA activity either by inhibition of water diuresis in rats or by reduction of the excretion of Na by the isolated kidney. Positive correlation has been demonstrated between heart rate and HS secretion.2. Heart-lung preparations from cats have been used to disclose additional factors controlling the rate of secretion of HS from heart muscle.3. Positive inotropic effects produced by administration of digoxin or adrenaline or by increase in peripheral resistance are associated with increases in the secretion of HS.4. Negative inotropic effects produced by high concentrations of procaine hydrochloride or by increase in venous return without change in external work are associated with decrease in HS secretion.

The isolation of a substance very closely resembling the 18-monoacetate of D-aldosterone from the venous blood of activated muscle and from contracting muscle

1. A renally active substance can be extracted in detectable quantity from 150 g flash-frozen active but not from 150 g flash-frozen flaccid striped muscle. This substance is identical to the 18-monoacetate of D-aldosterone (18-MA) in R(F) value in three solvent systems and in biological activity.2. The renally active substance is secreted into the blood stream by active but not by flaccid muscles.3. Bilateral stimulation of decentralized sciatic nerves causes diuresis, natriuresis, a rise in the clearances of creatinine and PAH without change in heart or respiratory rates, in cats under chloralose anaesthesia. These changes can be matched by I.V. infusion of ADH, 0.3-0.45 m-u./kg.min.4. The urinary changes caused by sciatic stimulation are not prevented by transection of the spinal cord but are abolished by hypophysectomy.5. Hence, like 18-MA, the muscle substance liberates ADH from the neurohypophysis.

Changes in the flow and composition of the urine induced by the 18 monoacetate of D-aldosterone, in cats

1. Isolated hearts release a steroid-like substance into the blood stream when venous return is decreased. This substance very closely resembles the 18 monoacetate of D-aldosterone (18 MA) in physicochemical and biological properties.2. Hence the changes in the flow and composition of the urine caused by infusions of the 18 MA have been examined in cats.3. The threshold effect of both 18 MA and of antidiuretic hormone (ADH) may be antidiuretic, but higher concentrations of both substances usually produce diuresis in cats under chloralose anaesthesia.4. Both ADH and 18 MA are antidiuretic in decerebrate cats.5. In decerebrate cats and in cats under chloralose anaesthesia the renal actions of 18 MA, 0.003-0.02 mug/kg.min are abolished by hypophysectomy: responses to ADH remain unchanged.6. 18 MA, 0.012 mug/kg.min causes the appearance of thioglycollate labile antidiuretic activity in blood taken from the terminal descending portion of the left lateral sinus.7. 18 MA, 0.05-0.15 mug/kg.min causes diuresis followed by antidiuresis in cats under chloralose anaesthesia. Hypophysectomy abolishes the diuretic phase of the response and uncovers the short latency of the antidiuretic. The antidiuresis is accompanied by reduction in the concentration of urinary Na and a fall in the ratio Na/K of the urine.

A renally active substance from heart muscle and from blood

1. A steroid-like compound has been isolated from cat heart muscle by thin-layer chromatography.2. This compound has been characterized by measurement of its R(F) values in two solvent systems.3. No similar substance could be detected in the 1 hr venous outputs of cat adrenals.4. It could not be detected in heart-lung circuit blood when the heart had been perfusing for 1(1/4)-1(1/2) hr at constant venous input and peripheral resistance. The compound was however extractable from the circuit blood 10-15 min after reduction in venous input.5. The actions of this compound on the isolated kidney resemble those of aldosterone but are of much shorter latency.6. The heart substance differs from aldosterone in R(F) values and has more than 10 times the renal activity of aldosterone when the two substances are equated (visually) for ability to reduce blue tetrazolium.