Escape from the sodium-retaining effects of mineralocorticoids

A noninvasive method to study the evolution of extracellular fluid volume in mice using time-domain nuclear magnetic resonance

Maintaining water homeostasis is fundamental for cellular function. Many diseases and drugs affect water balance and plasma osmolality. Water homeostasis studies in small animals require the use of invasive or terminal methods that make intracellular fluid volume and extracellular fluid volume (ECF) monitoring over time stressful and time consuming. We examined the feasibility of monitoring mouse ECF by a noninvasive method using time-domain nuclear magnetic resonance (TD-NMR). This technique allows differentiation of protons in a liquid environment (free fluid) from protons in soft tissues containing a majority of either small molecules (lean) or large molecules (fat). Moreover, this apparatus enables rapid, noninvasive, and repeated measurements on the same animal. We assessed the feasibility of coupling TD-NMR analysis to a longitudinal metabolic cage study by monitoring mice daily. We determined the effect of 24-h water deprivation on mouse body parameters and detected a sequential and overlapping decrease in free fluid and lean mass during water deprivation. Finally, we studied the effect of mineralocorticoids that are known to induce a transient increase in ECF but for which no direct measurements have been performed in mice. We showed, for the first time, that mineralocorticoids induced a transient ~15% increase in free fluid in conscious mice. TD-NMR is, therefore, the first method to allow direct measurement of discrete changes in ECF in conscious small animals. This method allows analysis of kinetic changes to stimuli before investigating with terminal methods and will allow further understanding of fluid disorders.

U-shaped relationship between left ventricular mass index and estimated glomerular filtration rate in patients with primary aldosteronism

Estimated glomerular filtration rate (eGFR) is an important topic in patients with primary aldosteronism (PA). However, the relationship between left ventricular structure and eGFR is unclear. We conducted a prospective, observational, and cross-sectional study to analyze 168 patients with PA and 168 propensity score-matched patients with essential hypertension (EH) as the control group, matched by age, gender, and systolic blood pressure. In the patients with PA, the eGFR was not correlated with left ventricular mass index (LVMI; r=-0.065, p=0.404), while in the patients with EH, the eGFR was negatively correlated with LVMI (r=-0.309, p<0.001). To test whether eGFR had a non-linear relationship with LVMI among the patients with PA, we stratified the patients with PA according to the tertile of eGFR (low, medium, and high tertile). The medium tertile of patients had a significantly lower LVMI than those in the other two tertiles (LVMI: 143.5±41.6, 120.5±40.5, and 133.1±34.3 g/m², from the lowest to highest tertile of eGFR; analysis of covariance p=0.032). The medium tertile of eGFR is associated with lowest LVMI. Patients with PA with high and low eGFR were associated with higher LVMI. The findings implied that the reasons for an increased LVMI in patients with PA may be different to those in patients with EH.

Evaluation of a low-dose desoxycorticosterone pivalate treatment protocol for long-term management of dogs with primary hypoadrenocorticism

Background

Lowering the dose of desoxycorticosterone pivalate (DOCP) for the treatment of dogs with primary hypoadrenocorticism (PH) decreases costs and could lead to increased owner motivation to treat their affected dogs.

Objective

To evaluate the efficacy of a low‐dose DOCP treatment protocol in dogs with PH.

Animals

Prospective study, 17 client‐owned dogs with naturally occurring PH (12 newly diagnosed, 5 previously treated with fludrocortisone acetate [FC]).

Methods

Dogs with newly diagnosed PH were started on 1.5 mg/kg DOCP SC; dogs previously treated with FC were started on 1.0‐1.8 mg/kg DOCP SC. Reevaluations took place at regular intervals for a minimum of 3 months and included clinical examination and determination of serum sodium and potassium concentrations. The DOCP dosage was adjusted to obtain an injection interval of 28‐30 days and to keep serum electrolyte concentrations within the reference interval.

Results

Median (range) follow‐up was 16.2 months (4.5‐32.3 months). The starting dosage was sufficient in all but 2 dogs and had to be significantly decreased after 2‐3 months to a median dosage (range) of 1.1 mg/kg (0.7‐1.8). Dogs 3 years of age or younger needed significantly higher dosages compared to older dogs. None of them, however, needed the 2.2 mg/kg DOCP dosage, recommended by the manufacturer.

Conclusions and Clinical Importance

A starting dosage of 1.5 mg/kg DOCP is effective in controlling clinical signs and serum electrolyte concentrations in the majority of dogs with PH. An additional dose reduction often is needed to maintain an injection interval of 28‐30 days. Young and growing animals seem to need higher dosages.

Primary Adrenal Insufficiency: Managing Mineralocorticoid Replacement Therapy

CONTEXT

Mineralocorticoid (MC) replacement therapy in patients with primary adrenal insufficiency (PAI) was introduced more than 60 years ago. Still, there are limited data on how MC substitution should be optimized, because MC dosing regimens have only been systematically investigated in a few studies. We review the management of current standard MC replacement therapy in PAI and its plausible impact on outcome.

DESIGN

Using PubMed, we conducted a systematic review of the literature from 1939 to 2017, with the following keywords: adrenal insufficiency, MC deficiency, aldosterone, cardiovascular disease, hypertension, and heart failure.

RESULTS

The current standard treatment consists of fludrocortisone (FC) given once daily in the morning, aiming at normotension, normokalemia, and plasma renin activity in the upper normal range. Available data suggest that patients with PAI may be underreplaced with FC as symptoms and signs indicating chronic MC underreplacement, such as salt craving and postural dizziness persist, in many treated patients with PAI. Data acquired from large registry-based studies show that glucocorticoid doses for replacement in PAI are higher than those estimated from endogenous production. Glucocorticoid overreplacement may reduce the need of MC replacement but may also be a consequence of inadequate MC replacement.

CONCLUSIONS

The commonly used MC replacement in PAI may not be adequate in some patients. Insufficient MC substitution may be responsible for poor cardiometabolic outcome and the failure to restore well-being adequately in patients with PAI. Well-designed studies oriented at optimizing MC replacement therapy are urgently needed.

Expression of urea transporters and their regulation

UT-A and UT-B families of urea transporters consist of multiple isoforms that are subject to regulation of both acutely and by long-term measures. This chapter provides a brief overview of the expression of the urea transporter forms and their locations in the kidney. Rapid regulation of UT-A1 results from the combination of phosphorylation and membrane accumulation. Phosphorylation of UT-A1 has been linked to vasopressin and hyperosmolality, although through different kinases. Other acute influences on urea transporter activity are ubiquitination and glycosylation, both of which influence the membrane association of the urea transporter, again through different mechanisms. Long-term regulation of urea transport is most closely associated with the environment that the kidney experiences. Low-protein diets may influence the amount of urea transporter available. Conditions of osmotic diuresis, where urea concentrations are low, will prompt an increase in urea transporter abundance. Although adrenal steroids affect urea transporter abundance, conflicting reports make conclusions tenuous. Urea transporters are upregulated when P2Y2 purinergic receptors are decreased, suggesting a role for these receptors in UT regulation. Hypercalcemia and hypokalemia both cause urine concentration deficiencies. Urea transporter abundances are reduced in aging animals and animals with angiotensin-converting enzyme deficiencies. This chapter will provide information about both rapid and long-term regulation of urea transporters and provide an introduction into the literature.

A urine-concentrating defect in 11β-hydroxysteroid dehydrogenase type 2 null mice

In aldosterone target tissues, 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) is coexpressed with mineralocorticoid receptors (MR) and protects the receptor from activation by glucocorticoids. Null mutations in the encoding gene, HSD11B2, cause apparent mineralocorticoid excess, in which hypertension is thought to reflect volume expansion secondary to sodium retention. Hsd11b2(-/-) mice are indeed hypertensive, but impaired natriuretic capacity is associated with significant volume contraction, suggestive of a urine concentrating defect. Water turnover and the urine concentrating response to a 24-h water deprivation challenge were therefore assessed in Hsd11b2(-/-) mice and controls. Hsd11b2(-/-) mice have a severe and progressive polyuric/polydipsic phenotype. In younger mice (∼2 mo of age), polyuria was associated with decreased abundance of aqp2 and aqp3 mRNA. The expression of other genes involved in water transport (aqp4, slc14a2, and slc12a2) was not changed. The kidney was structurally normal, and the concentrating response to water deprivation was intact. In older Hsd11b2(-/-) mice (>6 mo), polyuria was associated with a severe atrophy of the renal medulla and downregulation of aqp2, aqp3, aqp4, slc14a2, and slc12a2. The concentrating response to water deprivation was impaired, and the natriuretic effect of the loop diuretic bumetanide was lost. In older Hsd11b2(-/-) mice, the V2 receptor agonist desmopressin did not restore full urine concentrating capacity. We find that Hsd11b2(-/-) mice develop nephrogenic diabetes insipidus. Gross changes to renal structure are observed, but these were probably secondary to sustained polyuria, rather than of developmental origin.

Intrinsic control of sodium excretion in the distal nephron by inhibitory purinergic regulation of the epithelial Na(+) channel

PURPOSE OF REVIEW

This review summarizes the new evidence for an intrinsic control system in the aldosterone-sensitive distal nephron in which purinergic signaling regulates sodium transport and governs renal sodium excretion.

RECENT FINDINGS

Electrophysiological studies identify epithelial Na(+) channels (ENaC) as final effectors of purinergic signaling via P2Y(2) receptors in the distal nephron. Inhibition of ENaC by autocrine/paracrine purinergic signaling reduces sodium reabsorption allowing an appropriately graded pressure-natriuresis response when delivery of sodium to the distal nephron is high. Disruption of this intrinsic control mechanism decreases sodium excretion and therefore has a prohypertensive effect. Because purinergic inhibition of ENaC is tonic yet submaximal, its enhancement increases sodium excretion and therefore has an antihypertensive action.

SUMMARY

Purinergic inhibitory regulation of ENaC is a key component of an intrinsic control system that enables the distal nephron to respond appropriately to the delivered load of sodium. This control system is physiologically important and functions in parallel with extrinsic control by the renin-angiotensin-aldosterone system, enabling sodium excretion to keep pace with sodium intake, especially when intake is high, and thereby maintaining arterial blood pressure. Disruption of intrinsic control of sodium transport by the distal nephron likely contributes to diseases such as arterial hypertension.

Urea transport in the kidney

Urea transport proteins were initially proposed to exist in the kidney in the late 1980s when studies of urea permeability revealed values in excess of those predicted by simple lipid-phase diffusion and paracellular transport. Less than a decade later, the first urea transporter was cloned. Currently, the SLC14A family of urea transporters contains two major subgroups: SLC14A1, the UT-B urea transporter originally isolated from erythrocytes; and SLC14A2, the UT-A group with six distinct isoforms described to date. In the kidney, UT-A1 and UT-A3 are found in the inner medullary collecting duct; UT-A2 is located in the thin descending limb, and UT-B is located primarily in the descending vasa recta; all are glycoproteins. These transporters are crucial to the kidney's ability to concentrate urine. UT-A1 and UT-A3 are acutely regulated by vasopressin. UT-A1 has also been shown to be regulated by hypertonicity, angiotensin II, and oxytocin. Acute regulation of these transporters is through phosphorylation. Both UT-A1 and UT-A3 rapidly accumulate in the plasma membrane in response to stimulation by vasopressin or hypertonicity. Long-term regulation involves altering protein abundance in response to changes in hydration status, low protein diets, adrenal steroids, sustained diuresis, or antidiuresis. Urea transporters have been studied using animal models of disease including diabetes mellitus, lithium intoxication, hypertension, and nephrotoxic drug responses. Exciting new animal models are being developed to study these transporters and search for active urea transporters. Here we introduce urea and describe the current knowledge of the urea transporter proteins, their regulation, and their role in the kidney.

Purinergic inhibition of ENaC produces aldosterone escape

The mechanisms underlying "aldosterone escape," which refers to the excretion of sodium (Na(+)) during high Na(+) intake despite inappropriately increased levels of mineralocorticoids, are incompletely understood. Because local purinergic tone in the aldosterone-sensitive distal nephron downregulates epithelial Na(+) channel (ENaC) activity, we tested whether this mechanism mediates aldosterone escape. Here, urinary ATP concentration increased with dietary Na(+) intake in mice. Physiologic concentrations of ATP decreased ENaC activity in a dosage-dependent manner. P2Y(2)(-/-) mice, which lack the purinergic receptor, had significantly less increased Na(+) excretion than wild-type mice in response to high-Na(+) intake. Exogenous deoxycorticosterone acetate and deletion of the P2Y(2) receptor each modestly increased the resistance of ENaC to changes in Na(+) intake; together, they markedly increased resistance. Under the latter condition, ENaC could not respond to changes in Na(+) intake. In contrast, as a result of aldosterone escape, wild-type mice had increased Na(+) excretion in response to high-Na(+) intake regardless of the presence of high deoxycorticosterone acetate. These data suggest that control of ENaC by purinergic signaling is necessary for aldosterone escape.

Aldosterone and refractory hypertension

PURPOSE OF REVIEW

Evidence from clinical trials suggests that refractory hypertension is increasingly common. The underlying mechanisms are largely unknown but recent data have implicated increased aldosterone activity as an important mediator of resistance to routinely used antihypertensive agents.

RECENT FINDINGS

Epidemiological studies have suggested a significant rise in the prevalence of primary aldosteronism among patients with hypertension. This reflects the increasing use of an aldosterone-to-renin ratio as a screening tool. Recent reports have demonstrated that relative aldosterone excess is common in individuals with refractory hypertension, and that the use of aldosterone antagonists leads to better blood pressure control in such patients.

SUMMARY

These data highlight the potential role of aldosterone in the pathogenesis of hypertension. The syndrome of primary aldosteronism, however, encompasses a wide spectrum of disorders that will require better definition. Similarly, although aldosterone blockade is apparently beneficial in individuals with refractory hypertension, this evidence is not currently based on robust randomized, double-blind trial.

Functional and structural postglomerular alterations in the kidney of prehypertensive spontaneously hypertensive rats

The kidney plays a major role in the development of hypertension. Following the Borst-Guyton theory of an altered set-point for fluid and electrolyte homeostasis we aim to investigate functional and structural renal parameter during the development of hypertension. Therefore we focus on counter current exchange related factors. We compared 4 and 8 weeks old Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) concerning basic renal parameters as creatinine and phosphorus clearance and urinary osmolality. Mean arterial pressure (MAP) was measured intra-arterially. Vasa recta were investigated using immunohistochemistry for alpha-smooth-muscle actin (ASMA) and plastification for geometric analyses. Blood pressure was not yet significantly elevated in SHR at 4 weeks but at 8 weeks it was higher in SHR (116+/-7 vs. 102+/-4 mm Hg; p<0.01). Kidney weight/body weight ratio was lower in SHR at both ages. In 4 weeks old SHR, phosphorus clearance and urinary osmolality were decreased compared to WKY [0.02+/-0.01 vs. 0.05+/-0.02 (ml/min* 100 g BW) p < 0.03; 14.2+/-2.2 vs. 18.9+/-2.9 (osmol/kg*24 h urine) p < 0.051 indicating reduced tubular reabsorption. At 8 weeks phosphorus clearance and urinary osmolality were comparable to WKY. alpha-Actin was found in vasa recta in a 4-times higher degree in SHR with a predominant location in the outer medulla. Radii of vasa recta in the outer medulla decreased during development. In plastificated sections vasa recta of SHR revealed sphincter-like pattern. Functional and structural alterations related to the counter current exchanger are already evident in prehypertensive SHR. During development of hypertension both factors get adapted to higher blood pressure level. Sphincter-like structures in vasa recta suggest contractility of pericytes/vascular smooth muscle cells (vSMC). As these were just seen in SHR that might allude to a higher potential to contract. We conclude that differences in postglomerular structure and function may contribute to the development of hypertension in SHR.

Relative glomerular hyperfiltration in primary aldosteronism

Experimental and clinical data suggest that primary aldosteronism (PA) may be associated with cardiovascular hypertrophy and fibrosis, in part independent of the BP level. Whether PA may also result in specific deleterious effects on the kidneys was less studied. In 25 patients with tumoral PA, renal studies (urinary excretion of proteins, GFR, and effective renal plasma flow [ERPF], as clearances of technetium-labeled diethylene triaminopentaacetic acid and 131I-ortho iodohippurate, respectively) were performed both before and 6 mo after surgical cure. A control group consisting of patients with essential hypertension (EH) was studied before and after 6 mo of antihypertensive therapy. At baseline, PA and EH patients were similar with respect to demographic data, duration and level of hypertension, and GFR and ERPF. Urinary excretion of albumin and beta2 microglobulin were higher in PA than EH (88 +/- 26 versus 39 +/- 12 and 0.91 +/- 0.23 versus 0.26 +/- 0.19 mg/24 h, respectively; both P < 0.05). Adrenalectomy was followed by a decrease in arterial BP (by 28 +/- 3/13 +/- 2 mmHg), urinary excretion of albumin and beta2 microglobulin (by 48 +/- 19 and 0.53 +/- 0.21 mg/24 h, respectively), and GFR and ERPF (by 15 +/- 3 and 54 +/- 15 ml/min per 1.73 m(2), respectively). In EH, a similar decrease in pressure was associated with a decrease in albuminuria but no change in GFR or ERPF. In 17 of the 25 PA patients who received a 6-mo treatment of spironolactone, both GFR and ERPF decreased in parallel with BP, similar to what was observed after surgery. These data suggest that PA was associated with relative hyperfiltration, unmasked after suppression of aldosterone excess.

Aldosterone biosynthesis, regulation, and classical mechanism of action

Circulating aldosterone is principally made in the glomerulosa zone of the adrenal cortex by a series of enzyme steps leading to the conversion of cholesterol to aldosterone. Uniquely, aldosterone's production is regulated at two critical enzyme steps: (1) early in its biosynthetic pathway (the conversion of cholesterol to pregnenolone cholesterol side chain cleavage enzyme) and (2) late (the conversion of corticosterone to aldosterone by aldosterone synthase). A variety of factors modify aldosterone secretion--the most important are angiotensin II (AngII), the end-product of the renin-angiotensin system (RAS), and potassium. However ACTH, neural mediators and natriuretic factors also contribute at least over the short run. Aldosterone's classical epithelial effect is to increase the transport of sodium across the cell in exchange for potassium and hydrogen ions. Although still controversial, there is an increasing body of data that supports the hypothesis that aldosterone can be synthesized in tissues outside of the adrenal cortex, specifically in the heart and the vasculature. Aldosterone's biosynthesis appears to be regulated in these tissues similar to what occurs in the adrenal cortex. The role of this extra adrenal aldosterone production in health and disease is as of yet undetermined.

Hyponatremia in critically ill neurological patients

BACKGROUND

Hyponatremia is the most common and important electrolyte disorder encountered in the neurologic intensive care unit (NICU). Advances in our knowledge of the pathophysiological mechanisms at play in patients with acute neurologic disease have improved our understanding of this derangement.

REVIEW SUMMARY

Evaluation of hyponatremia requires a structured approach beginning with the measurement of serum and urine osmolalities. Most cases of hyponatremia in the NICU are associated with serum hypotonicity. Iatrogenic causes, most conspicuously inadequate tonicity of intravenous fluids, should be promptly identified and removed when possible. Two main mechanisms are responsible for most non-iatrogenic cases of hyponatremia in patients with neurologic or neurosurgical disease: inappropriate secretion of antidiuretic hormone (SIADH) and cerebral salt wasting syndrome (CSW). Distinction between these two syndromes may be difficult and must be based on an accurate assessment of the patient's volume status. SIADH is associated with normal or slightly expanded volume status and should be treated with fluid restriction. Patients with CSW are hypovolemic and require adequate fluid and sodium replacement. Correction of hyponatremia should not exceed 8 to 10 mmol/L over any 24-hour period to avoid the risk of osmotic demyelination.

CONCLUSIONS

Hyponatremia may complicate the clinical course of many acute neurologic and neurosurgical disorders. It is most often iatrogenic causes, CSW, or SIADH. Physicians working with critically ill neurologic patients should be familiar with management strategies addressing these underlying pathophysiological mechanisms.

Potassium supplementation improves the natriuretic response to central volume expansion in primary aldosteronism

Potassium depletion induced by dietary potassium restriction is known to cause sodium retention, while potassium supplementation is known to increase urinary sodium excretion. However, the ability of potassium deficiency to affect mineralocorticoid-induced sodium retention in aldosterone-producing adenoma (APA) subjects has not been extensively investigated, neither in baseline conditions nor when facilitating natriuresis through a physiological manoeuver such as central blood volume expansion. With the aim of testing the hypothesis that potassium supplementation would attenuate the mineralocorticoid-induced sodium retention, in 7 APA patients elevation of serum potassium was obtained by infusion of isosmotic potassium chloride (KCl) at a constant rate of 36 mmol/h for a 2-hour period for 5 consecutive days. The same patients were also submitted to acute central volume expansion by head-out water immersion (WI) associated with either low or normal serum potassium levels. The assessment of natriuresis in baseline condition and during WI was also performed in 10 age-matched control subjects. Central hypervolemia by WI induced a significant natriuretic response in APA hypokalemic subjects; on the other hand, in the same APA subjects giving potassium supplementation, WI-induced urinary sodium excretion was significantly higher (P <.001) than that obtained during WI at normal potassium intake (hypokalemic condition). Blood pressure responses and hormonal profiles were almost superimposable during the 2 WI experiments performed at different serum potassium levels. By confirming that amelioration of hypokalemia attenuates mineralocorticoid-induced sodium retention, this study also suggests that potassium intake may represent an important determinant of mineralocorticoid escape.

Regulation of NHE3, NKCC2, and NCC abundance in kidney during aldosterone escape phenomenon: role of NO

Escape from aldosterone-induced renal NaCl retention is an important homeostatic mechanism in pathophysiological states in which plasma aldosterone levels are inappropriately elevated, e.g., in primary aldosteronism. Our previous studies demonstrated that the escape process occurs largely as a result of a marked suppression of the abundance of the thiazide-sensitive Na-Cl cotransporter (NCC) of the distal convoluted tubule but have also demonstrated a paradoxical increase in the protein abundance of the apical Na/H exchanger of the proximal tubule (NHE3). In the present study, we confirmed the increase in NHE3 and also showed that a similar increase in NHE3 protein abundance occurs in escape from ANG II-mediated NaCl retention. To investigate the potential role of nitric oxide (NO) in the observed upregulation of NHE3, we repeated the aldosterone escape experiment with a superimposed infusion of a NO synthase inhibitor, NG-nitro-l-arginine methyl ester (l-NAME). l-NAME infusion abolished the increase in NHE3 protein abundance. Furthermore, in a different experiment, NO synthase inhibition uncovered an associated decrease in the abundance of the Na-K-2Cl cotransporter (NKCC2) of the thick ascending limb, not seen with simple aldosterone escape. However, NO synthase inhibition did not block the decrease in NCC abundance normally seen with aldosterone escape. Furthermore, l-NAME infusion in aldosterone-treated rats markedly decreased both NHE3 and NKCC2 protein abundance, without changes in the corresponding mRNA levels. We conclude that NHE3 and NKCC2 protein abundances in kidney are positively regulated by NO and that the increase in NHE3 abundance seen in the aldosterone escape phenomenon is NO dependent.

Molecular approaches to urea transporters

Urea plays a critical role in the urine-concentrating mechanism in the inner medulla. Physiologic data provided evidence that urea transport in red blood cells and kidney inner medulla was mediated by specific urea transporter proteins. Molecular approaches during the past decade resulted in the cloning of two gene families for facilitated urea transporters, UT-A and UT-B, encoding several urea transporter cDNA isoforms in humans, rodents, and several nonmammalian species. Polyclonal antibodies have been generated to the cloned urea transporter proteins, and the use of these antibodies in integrative animal studies has resulted in several novel findings, including: (1) the surprising finding that UT-A1 protein abundance and urea transport are increased in the inner medulla during conditions in which urine concentrating ability is reduced; (2) vasopressin increases UT-A1 phosphorylation in rat inner medullary collecting duct; (3) UT-A protein abundance is upregulated in uremia in both liver and heart; and (4) UT-B is expressed in many nonrenal tissues and endothelial cells. This review will summarize the knowledge gained from using molecular approaches to perform integrative studies into urea transporter protein regulation, both in normal animals and in animal models of human diseases, including studies of uremic rats in which urea transporter protein is upregulated in liver and heart.

Mineralocorticoid regulation of cyclooxygenase-2 expression in rat renal medulla

The renal inner medulla and its distal one-third, the papilla, are major sites of prostanoid synthesis involved in water and electrolyte homeostasis. These sites contain variable levels of cyclooxygenase (COX)-2, a key prostaglandin synthase enzyme that is sensitive to adrenal steroids. Immunoreactive renal medullary COX-2, restricted to interstitial cells in control adult rats, shows a gradient of intense staining at the tip of the papilla that gradually diminishes to undetectable levels in the proximal inner medulla. We used adrenalectomy (ADX) and steroid replacement to investigate the effects of steroids on papillary COX-2. Immunoblots demonstrate that papillary COX-2 was reduced by one-half after 2 wk ADX; glucocorticoid replacement ameliorated the decline but not to control levels. Mineralocorticoid (deoxycorticosterone acetate; DOCA) replacement stimulated papillary COX-2 more than fivefold over control; both the intensity of immunostaining and the numbers of COX-2-positive cells in the inner medulla increased. Similar stimulation of papillary COX-2 resulted from DOCA treatment of normal control rats, but the response was blunted in rats fed a low-salt diet and absent in Brattleboro rats. DOCA treatment of mouse renal medullary interstitial cells in culture had no effect, but increased tonicity of the culture medium with NaCl caused strong upregulation of COX-2. Urea, a permeant molecule, had no effect. Together, these results suggest that mineralocorticoids lead to upregulation of COX-2 in rat renal medulla by indirect pathways, probably involving induced electrolyte hypertonicity in the interstitial fluid.

Mammalian urea transporters

Urea plays a key role in the urine-concentrating mechanism. Physiologic and molecular data demonstrate that urea transport in kidney and red blood cells occurs by specific urea transporter proteins. Two gene families for facilitated urea transporters, UT-A and UT-B, and several urea transporter cDNA isoforms have been cloned from human, rat, mouse, and several non-mammalian species. Polyclonal antibodies have been generated to many of the urea transporter proteins, and several novel findings have resulted from their use in integrative animal studies. For example, (a) vasopressin increases the phosphorylation of UT-A1 in rat inner medullary collecting duct; (b) UT-A1 protein abundance is increased in the rat inner medulla during conditions in which urine-concentrating ability is reduced; and (c) urea transporters are expressed in non-renal tissues, and UT-A protein abundance is up-regulated in uremia in both liver and heart. In addition to the facilitated urea transporters, functional evidence exists for active urea transport in the kidney collecting duct. This review summarizes the physiologic evidence for the existence of facilitated and active urea transporters, the molecular biology of the facilitated urea transporter gene families and cDNAs, and integrative studies into urea transporter protein regulation, both in the kidney and in other organs.

GH increases extracellular volume by stimulating sodium reabsorption in the distal nephron and preventing pressure natriuresis

Although sodium retention and volume expansion occur during GH administration, blood pressure is decreased or unchanged. The aim was to study the effect of short- and long-term GH replacement in adults on sodium balance, renal hemodynamics, and blood pressure. Ten adults with severe GH deficiency were included into a 7-d, randomized, placebo-controlled, cross-over trial followed by 12 months of open GH replacement. All measurements were performed under metabolic ward conditions. Extracellular water (ECW) was determined using multifrequency bioelectrical impedance analysis. Renal plasma flow and glomerular filtration rate were assessed using renal paraminohippurate and Cr(51) EDTA clearances, respectively. Renal tubular sodium reabsorption was assessed using lithium clearance. Plasma renin activity (PRA), plasma concentrations of angiotensin II, aldosterone, atrial natriuretic peptides and brain natriuretic peptides (BNP) and 24-h urinary norepinephrine excretion were measured. Seven days of GH treatment decreased urinary sodium excretion. Lithium clearance as a marker of proximal renal tubular sodium reabsorption was unaffected by GH treatment. ECW was increased after both short- and long-term treatment. This increase was inversely correlated to the decrease in diastolic blood pressure (r = -0.70, P = 0.02) between baseline and 12 months. Short-term treatment increased PRA and decreased BNP. The increase in PRA correlated with an increase in 24-h urinary norepinephrine excretion (r = 0.77, P < 0.01). Glomerular filtration rate and renal plasma flow did not change during treatment. The sodium- and water-retaining effect of GH takes place in the distal nephron. The sustained increase in ECW in response to GH is associated with an unchanged or decreased blood pressure. This together with unchanged or decreased atrial natriuretic peptides and BNP may prevent pressure-induced escape of sodium.

Hyperaldosteronism in a cat with metastasised adrenocortical tumour

In a 12-year-old male shorthaired cat with attacks of hypokalaemic muscular weakness in spite of oral potassium supplementation, highly elevated plasma aldosterone concentrations in combination with low plasma renin activity pointed to primary hyperaldosteronism. Ultrasonography and computed tomography revealed a large left-sided adrenal tumour growing into the phrenicoabdominal vein and the caudal vena cava. The tumour and its intravascular extension were surgically removed, but the subsequent stenosis of the caudal vena cava caused congestion and renal failure. At autopsy pulmonary micrometastases of the aldosteronoma were found.

Role of nitric oxide in modulating renal function and arterial pressure during chronic aldosterone excess

Chronic aldosterone (Aldo) excess is associated with transient sodium retention, extracellular fluid volume expansion, renal vasodilation, and hypertension. The purpose of this study was to determine the role of nitric oxide (NO) in mediating the renal vasodilation and the escape from the sodium-retaining actions of Aldo. To achieve this goal, we examined the long-term effects of Aldo (15 microgram. kg-1. min-1 for 7 days) in conscious, chronically instrumented control dogs (n = 9) and in dogs (n = 12) pretreated with the NO synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 10 microgram. kg-1. min-1). In control dogs, Aldo caused a transient sodium retention (126 +/- 6 to 56 +/- 2 meq/day) followed by a return of sodium excretion to normal levels. Aldo also increased renal plasma flow by 15% (205 +/- 13 to 233 +/- 16 ml/min), glomerular filtration rate by 20% (72 +/- 3 to 87 +/- 5 ml/min), and arterial pressure from 90 +/- 3 to 102 +/- 3 mmHg. Aldo increased urinary nitrate/nitrite excretion by 60% in the control dogs. Although the sodium-retaining (144 +/- 7 to 56 +/- 7 meq/day) and arterial pressure (122 +/- 6 to 136 +/- 5 mmHg) responses to Aldo were the same in dogs pretreated with L-NAME compared with control, the renal hemodynamic response was markedly attenuated. The results of this study suggest that NO plays an important role in mediating the renal vasodilation during chronic Aldo excess.

Effect of dibutyryl cyclic AMP on plasma renin activity in normal men and patients with primary aldosteronism

Dibutyryl cyclic AMP (DBcAMP) directly stimulates the release of renin from the juxtaglomerular (JG) cells in vitro. We investigated the effect of DBcAMP on plasma renin activity (PRA) in 6 normal men and in 8 patients with primary aldosteronism (PA). A 20-min infusion of 0.33 mg/kg/min of DBcAMP significantly increased PRA in normal men, but had little effect on PRA in patients with PA. Infusion of DBcAMP significantly reduced the blood pressure and the levels of serum sodium and potassium in normal men and the patients with PA. Infusion of DBcAMP significantly increased urine volume in normal men, but not in patients with PA. Urinary excretion of sodium increased in both groups after the infusion of DBcAMP. Thus, DBcAMP did not stimulate renin release in patients with PA, suggesting that the chronic excess production of aldosterone suppresses the release of renin from JG cells.

The resistance of the Wistar/Furth rat strain to steroid hypertension

We have previously reported that the Wistar/Furth (W/Fu) rat strain is resistant to mineralocorticoid hypertension. In the current study, we have examined renal mRNA levels for mineralocorticoid receptor (MR), glucocorticoid receptor (GR), renin and Na+, K(+)-ATPase in response to treatment with mineralocorticoids. Uninephrectomized male Wistar (WI) and W/Fu rats were treated with aldosterone or deoxycorticosterone acetate (DOCA) and were given 1% NaCl to drink. Rats were sacrificed after 1, 3 or 7 days of treatment. Renal MR and ATPase mRNA levels were significantly reduced in aldosterone and DOCA-treated WI rats (e.g. MR was 30% on day 3 and ATPase was 50% of control on day 7 of aldosterone treatment). Unexpectedly, GR mRNA levels paralleled the changes in MR. In W/Fu rats the level of message was either unchanged or only moderately altered by this treatment. In vivo administration of the MR antagonist RU28318 or the GR antagonist RU38486 to WI rats for 4 days reduced renal mRNA levels for both subunits of ATPase. In the W/Fu rat, this treatment resulted in no change in the alpha subunit and an increase in the beta subunit of ATPase. In preliminary studies, we have determined that the W/Fu rat is also resistant to dexamethasone-induced hypertension. These studies suggest that altered MR- and GR-mediated mechanisms may contribute to the resistance of the W/Fu rat strain to steroid-induced hypertension.

Interactions between glucocorticoids and mineralocorticoids in the regulation of renal electrolyte transport

The enzyme 11 beta-hydroxy steroid dehydrogenase (11 beta-OHSD) was described and its location in various organs noted more than 30 years ago (Mahesh and Ulrich, 1960; Jenkins, 1966). 11 beta-OHSD inactivates circulating glucocorticoids by transforming the hydroxyl group at the 11-carbon to a keto group. This chemical reaction has taken on a greater degree of physiologic and clinical significance in recent years. It has been suggested that 11 beta-OHSD, present in mineralocorticoid target tissues, can act as a 'guardian' over the mineralocorticoid receptor by transforming circulating endogenous glucocorticoids to their respective 'biologically inert' 11-dehydro derivatives (Edwards et al., 1988; Funder et al., 1988). These derivatives do not bind to mineralocorticoid receptors (MR) while both their parent compounds and mineralocorticoids bind to cloned MR with equal affinity (Arriza et al., 1987). 11 beta-OHSD has generated a growing sense of scientific excitement since this enzyme may represent one of a family of metabolic pathways or mechanisms which can regulate steroid induced renal reabsorption of sodium. Such 'protective' enzymatic pathways, present in the kidney and elsewhere, may not only control the access of glucocorticoids to MR, but control the access of glucocorticoids to glucocorticoid receptors (GR) (Teelucksingh et al., 1990; Monder, 1990) as well as access of mineralocorticoids to their own receptors. This review will focus on this concept of a family of protective enzymatic pathways and the possible physiological implications.

Potassium supplementation ameliorates mineralocorticoid-induced sodium retention

Potassium depletion induced by dietary potassium restriction causes sodium retention while potassium supplementation augments urinary sodium excretion. The role of external potassium balance in modulating mineralocorticoid-induced sodium retention in humans is unknown. Accordingly, eight healthy subjects were studied at the Clinical Research Center receiving a constant diet providing (per kg body wt) sodium 2.5 mmol, potassium 1.1 mmol daily. After establishing basal sodium and potassium balance over three days, each subject received 9 alpha-fludrocortisone 0.4 mg/day for 10 days. Subjects were studied twice, four to eight weeks apart, in a double blind, randomized crossover design receiving either placebo or additional KCl (80 mmol/day) over the 10 day study period. Serum potassium concentrations were unchanged from basal values on KCl while the values fell (4.1 +/- 0.1 vs. 3.4 +/- 0.1 mmol/liter, P = 0.01) on placebo. Urinary sodium excretion decreased with fludrocortisone administration in both groups, but this decrease reached significance only in the placebo group. Furthermore, during fludrocortisone administration the sodium excretion rates on KCl were significantly higher compared to the values noted on placebo (134 +/- 8 vs. 112 +/- 13 mmol/day, P = 0.01). Body weight recorded after 10 days of fludrocortisone administration was higher on placebo compared to KCl (72.3 +/- 2.8 vs. 71.6 +/- 2.8 kg, P = 0.01). Plasma renin activity, and aldosterone concentrations decreased on fludrocortisone while atrial natriuretic peptide levels increased. These studies suggest that amelioration of hypokalemia attenuates mineralocorticoid-induced sodium retention. Therefore, potassium depletion may contribute to the mineralocorticoid-induced sodium retention.

Diuretic and natriuretic responses to ANF in the presence and absence of renal nerves in DOCA-salt hypertensive rats

To determine if renal nerves contributes in the renal response to atrial natriuretic factor (ANF) in DOCA-salt hypertensive rats, diuretic and natriuretic responses to ANF were measured in Inactin (0.1 g/kg, i.p) anesthetized rats with unilateral renal denervation. Rats were assigned to either a control group (108 +/- 6 mmHg), or one of two DOCA-salt groups (injected with deoxycorticosterone acetate, DOCA, 25 mg/week, and given 0.9% saline to drink for 4 weeks); a) DOCA-salt group (137 +/- 6 mmHg) and b) DOCA-salt-BPC group (with blood pressure controlled at the level of the femoral artery (102 +/- 3 mmHg) by an occluder on the abdominal aorta proximal to the right renal artery). Urine flow and sodium excretion in response to ANF infusion (0.3 micrograms/min/kg) were measured from intact and denervated kidneys of control and DOCA-salt treated rats. ANF infusion produced a significant increase in diuresis and natriuresis in all three groups of rats. Urine flow and sodium excretion in response to ANF were significantly less in the intact kidney but not the denervated kidneys of the DOCA-salt rats compared to control rats. These results indicate that renal nerves contribute to the blunted renal responses to ANF in DOCA-salt rats. Renal responses also were significantly smaller in both intact and denervated kidneys of DOCA-salt-BPC rats (in which arterial pressure was reduced) compared to DOCA-salt rats. Overall, these results indicate that both renal nerves and arterial pressure determine the natriuretic and diuretic actions of ANF in DOCA-salt hypertensive rats.

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.

Abnormal pressure natriuresis. A cause or a consequence of hypertension?

In all forms of chronic hypertension, the renal-pressure natriuresis mechanism is abnormal because sodium excretion is the same as in normotension despite the increased blood pressure. However, the importance of this resetting of pressure natriuresis as a cause of hypertension is controversial. Theoretically, a resetting of pressure natriuresis could necessitate increased blood pressure to maintain sodium balance or it could occur secondarily to hypertension. Recent studies indicate that, in several models of experimental hypertension (including angiotensin II, aldosterone, adrenocorticotrophic hormone, and norepinephrine hypertension), a primary shift of renal-pressure natriuresis necessitates increased arterial pressure to maintain sodium and water balance. In genetic animal models of hypertension, there also appears to be a resetting of pressure natriuresis before the development of hypertension. Likewise, essential hypertensive patients exhibit abnormal pressure natriuresis, although the precise cause of this defect is not clear. It is likely that multiple renal defects contribute to resetting of pressure natriuresis in essential hypertensive patients. With long-standing hypertension, pathological changes that occur secondary to hypertension must also be considered. By analyzing the characteristics of pressure natriuresis in hypertensive patients and by comparing these curves to those observed in various forms of experimental hypertension of known origin, it is possible to gain insight into the etiology of this disease.

The effect of adrenal surgery on plasma atrial natriuretic factor and sodium escape phenomenon in patients with primary aldosteronism

Plasma concentrations of atrial natriuretic factor and some vasoactive substances were determined in 8 patients with aldosterone-producing adenoma, 10 with idiopathic adrenal hyperplasia, 10 normotensive subjects and 12 patients with essential hypertension. Plasma atrial natriuretic factor concentration in patients with aldosterone-producing adenoma was the highest among the examined groups. Adrenal surgery reduced plasma concentrations of atrial natriuretic factor and aldosterone concomitant with the elevation in urinary sodium excretion, plasma renin activity and urinary sodium-to-potassium ratio. Withdrawal of trilostane (3 beta-hydroxysteroid dehydrogenase inhibitor) in patients with idiopathic adrenal hyperplasia increased plasma concentrations of atrial natriuretic factor and aldosterone, and decreased the urinary sodium-to-potassium ratio, plasma renin activity and urinary sodium excretion. However, reduced urinary sodium excretion following trilostane treatment returned to the control level successively despite the high levels of plasma atrial natriuretic factor and aldosterone. Acute infusion of saline remarkably increased plasma atrial natriuretic factor concentration in patients with idiopathic adrenal hyperplasia and aldosterone-producing adenoma. These results suggest that a high level of atrial natriuretic factor is a characteristic feature in patients with aldosterone-producing adenoma caused chiefly by the expansion of extracellular fluid volume, and circulating atrial natriuretic factor may contribute to regulation of the sodium escape phenomenon in patients with aldosterone-producing adenoma or idiopathic adrenal hyperplasia.

Evaluation of lithium clearance as a marker of proximal tubule sodium handling

Estimations of proximal tubule sodium reabsorption with the FELi method come closer to direct measurements than any other indirect method. There is little doubt that most lithium reabsorption takes place in the proximal tubules, very likely in proportion to the reabsorption of sodium and water. It is also likely that changes in proximal tubule sodium reabsorption due to changes in volume status are paralleled by changes in proximal tubule lithium reabsorption, at least in the superficial nephrons. Nonetheless, changes in FELi probably do not purely reflect changes in proximal reabsorption, since lithium is also handled beyond the proximal tubules. Acknowledged problems are lithium reabsorption in Henle's loop and in the late distal and collecting tubules. The latter occurs in the rat and the dog, but not or much less in men. Sodium restriction enhances this lithium transport considerably. It is as yet uncertain whether other conditions, such as increased vasopressin activity or lowering of renal perfusion pressure, also influence this transport. Amiloride appears to prevent this reabsorption of lithium. Therefore, this drug can be used in lithium clearance studies whenever unwanted "distal" lithium reabsorption is expected. Lithium reabsorption in Henle's loop forms a greater problem as it cannot be prevented by any drug without influencing proximal tubule reabsorption. It is estimated that about 7% of the filtered lithium (one-tenth of total lithium reabsorption) is normally taken up here, preferentially in deep nephrons. In view of studies with furosemide, this reabsorption probably varies with sodium intake, but the proportion of this variation to that of proximal tubule lithium reabsorption is obscure. This remains an uncertain factor in any circumstance where the lithium clearance method is used. In some conditions the change in FELi may be so large relative to the expected changes in proximal reabsorption, that use of FELi as marker of end-proximal solute delivery seems unjustified. Disproportionately large suppression is likely during mineralo-corticoid-induced volume expansion, and stimulation during prostaglandin synthesis inhibition and vasopressin. Based on observations in these conditions the potential range of lithium reabsorption in the loop of Henle would be 0 to 15% of filtered load. In this review attention was paid mainly to the validity of lithium clearance as a pure "proximal marker". Many of our interpretations suffer from incomplete certainty with respect to the renal effects of tested maneuvers, a problem which is acknowledged.(ABSTRACT TRUNCATED AT 400 WORDS)

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

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

Specific binding of atrial natriuretic factor to renal glomeruli in Doca- and Doca-salt-treated rats correlation with atrial and plasma levels

Since volume expansion and high blood pressure (BP) are known stimuli of atrial natriuretic factor (ANF) release, and since this peptide may be involved in mineralocorticoid escape, we investigated the effects of chronic deoxycorticosterone (DOCA) and DOCA-NaC1 treatment on renal glomerular ANF receptor density and affinity in relation to atrial and plasma ANF levels. An increase in plasma immunoreactive ANF (IR-ANF) was observed both after two and four weeks of treatment. IR-ANF concentrations were elevated in the left atrium only in four-week DOCA treated rats. Administration of the mineralocorticoid alone resulted in a decreased density of glomerular ANF receptors in both time periods investigated. DOCA-NaC1-treated animals presented an increased receptor density during the pre-hypertensive stage (2 weeks) and a reduced density in the later hypertensive period (4 weeks). Receptor affinity in both groups was identical to that in the controls after 2 weeks and was augmented after 4 weeks of treatment. Our data suggest that the down-regulation of renal glomerular ANF receptors during chronic DOCA-NaC1 administration may play a role in the maintenance of high BP in this model of volume-expanded hypertension.

Plasma atrial natriuretic peptide in DOCA-NaCl-treated rats

In order to assess the possible role of atrial natriuretic peptide (ANP) in the development of deoxycorticosterone (DOCA)-NaCl-induced hypertension, plasma immunoreactive ANP concentration was compared with sodium balance and blood pressure in NaCl- or DOCA-NaCl-treated rats. Both NaCl-and DOCA-NaCl-loading increased plasma ANP levels (to 86 +/- 8.1 and 105 +/- 12 pg ml-1 respectively; 47 +/- 6.7-60 +/- 4.6 pg ml-1 in controls), which were correlated to sodium intake and excretion. In DOCA-NaCl-treated rats, the highest ANP levels (105 +/- 12 pg ml-1) were found 4 weeks after the beginning of DOCA-NaCl treatments. Along with the development of DOCA-NaCl hypertension in 1-kidney-DOCA-NaCl-treated rats, however, plasma ANP concentration did not rise further. We conclude that secretion of ANP into the circulation is increased during DOCA-NaCl treatment. Elevated blood pressure does not stimulate ANP release in DOCA-NaCl-treated rats further.

Atrial natriuretic peptide transcription, secretion, and glomerular receptor activity during mineralocorticoid escape in the rat

The mechanisms that mediate renal "escape" from the sodium-retaining effects of mineralocorticoids are incompletely understood. This study was undertaken to determine whether atrial natriuretic peptide (ANP) may play a role in the escape phenomenon. Immunoreactive ANP in rat plasma increased 2.5-fold above baseline values at 12 and 24 h after a single depot injection of desoxycorticosterone acetate in oil and returned to baseline thereafter. In addition, specific pre-pro-ANP messenger RNA content in rat atria was significantly elevated as early as 12 h after mineralocorticoid administration and remained elevated at 24, 48, and 72 h, indicating a prompt and sustained increase in ANP biosynthesis. Renal glomerular ANP receptor density was down-regulated appropriately with rising plasma ANP levels, and receptor affinity was unchanged. Thus, mineralocorticoid administration in the rat is a powerful stimulus for ANP release and for atrial myocyte ANP synthesis, which suggests a potential role for this hormone in overriding mineralocorticoid-induced renal sodium retention.

Immunoreactive atrial natriuretic hormone levels increase in deoxycorticosterone acetate-treated pigs

Extensive evidence reported here and elsewhere indicates a hormonal role for atrial natriuretic factor. In the light of this evidence, it appears that atrial natriuretic hormone is a more appropriate term for these peptides than atrial natriuretic factor. Plasma levels of immunoreactive atrial natriuretic hormone were measured daily in seven pigs before and 1 week after subcutaneous implantation of deoxycorticosterone acetate (DOCA). Nine other animals underwent daily measurements of mean arterial pressure and central venous pressure during similar treatments. Plasma immunoreactive atrial natriuretic hormone levels rose progressively during the first 3 days after implantation, from a basal level of 60 +/- 9 pmol/L to a peak level of 159 +/- 21 pmol/L (p less than 0.05), and they remained significantly elevated throughout the rest of the 7-day observation period. In two animals that were restudied 6 weeks after DOCA implantation, plasma immunoreactive atrial natriuretic hormone had returned to preimplantation levels. The rise in plasma hormone levels after DOCA implantation closely paralleled the previously reported time course of mineralocorticoid escape. Whether atrial natriuretic hormone plays an important part in the escape phenomenon remains to be determined.