Escape from the sodium-retaining effects of mineralocorticoids: role of ANF and intrarenal hormone systems

Strategies to address diabetic kidney disease burden in Mexico: a narrative review by the Mexican College of Nephrologists

Chronic kidney disease (CKD) is a growing global public health challenge worldwide. In Mexico, CKD prevalence is alarmingly high and remains a leading cause of morbidity and mortality. Diabetic kidney disease (DKD), a severe complication of diabetes, is a leading determinant of CKD. The escalating diabetes prevalence and the complex regional landscape in Mexico underscore the pressing need for tailored strategies to reduce the burden of CKD. This narrative review, endorsed by the Mexican College of Nephrologists, aims to provide a brief overview and specific strategies for healthcare providers regarding preventing, screening, and treating CKD in patients living with diabetes in all care settings. The key topics covered in this review include the main cardiometabolic contributors of DKD (overweight/obesity, hyperglycemia, arterial hypertension, and dyslipidemia), the identification of kidney-related damage markers, and the benefit of novel pharmacological approaches based on Sodium-Glucose Co-Transporter-2 Inhibitors (SGLT2i) and Glucagon-Like Peptide-1 Receptor Agonists (GLP-1 RA). We also address the potential use of novel therapies based on Mineralocorticoid Receptor Antagonists (MRAs) and their future implications. Emphasizing the importance of multidisciplinary treatment, this narrative review aims to promote strategies that may be useful to alleviate the burden of DKD and its associated complications. It underscores the critical role of healthcare providers and advocates for collaborative efforts to enhance the quality of life for millions of patients affected by DKD.

Unilateral adrenalectomy for a drug-resistant bilateral primary aldosteronism with heart failure: pathophysiology and surgical indication

BACKGROUND

Patients with bilateral primary aldosteronism (PA) generally are treated with antihypertensive drugs, but optimal treatment for patients with complications due to refractory hypertension has not been established. In this report, we present a case with bilateral PA who presented with persistent hypertension, despite treatment with 6 drugs, and left-dominant heart failure, which was improved after unilateral adrenalectomy.

CASE PRESENTATION

A 61-year-old man was admitted to our hospital because of severe left-dominant heart failure. His heart rhythm was atrial fibrillation and the left ventricle was diffusely hypertrophic and hypokinetic. Coronary arteries were normal on coronary arteriogram. Primary aldosteronism was suspected based on severe hypokalemia (2.5 mEq/L) and plasma aldosterone concentration (PAC; 1,410 pg/mL). Although computed tomography (CT) showed a single left cortical nodule, adrenal vein sampling (AVS) indicated bilateral PA. Early in the case, heart failure and hyperkalemia in this patient were improved by treatment with a combination of 6 antihypertensive drugs (spironolactone 25 mg/day, eplerenone 100 mg/day, azosemide 60 mg/day, tolvaptan 7.5 mg/day, enalapril 5 mg/day, and bisoprolol fumarate 10 mg/day); however, heart failure relapsed after four months of treatment. We hypothesized that hypertension caused by excess aldosterone was inducing the patient's heart failure. In order to reduce aldosterone secretory tissue, a laparoscopic adrenalectomy was performed for the left adrenal gland, given the higher level of aldosterone from the left gland compared to the right. Following surgery, the patient's heart failure was successfully controlled despite the persistence of high PAC. Treatment with anti-hypertensive medications was reduced to two drugs (eplerenone 100 mg/day and bisoprolol fumarate 10 mg/day). In order to elucidate the mechanism of drug resistance, immunohistochemistry (IHC) and real time-polymerase chain reaction (RT-PCR) assays were performed to assess the expression of steroidogenic factor 1 (SF-1), a regulator of steroid synthesis in adrenal tissue. IHC and RT-PCR demonstrated that the expression of SF-1 in this patient (at both the protein and mRNA levels) was higher than that observed in unilateral PA cases that showed good responsivity to drug treatment.

CONCLUSIONS

Unilateral adrenalectomy to reduce aldosterone secretory tissue may be useful for patients with drug-refractory, bilateral PA. Elevated expression of SF-1 may be involved in drug resistance in PA.

Correlation between kidney sodium and potassium handling and the renin-angiotensin-aldosterone system in children with hypertensive disorders

BACKGROUND

Urine sodium and potassium are used as surrogate markers for dietary consumption in adults with hypertension, but their role in youth with hypertension and their association with components of the renin-angiotensin-aldosterone system (RAAS) are incompletely characterized. Some individuals with hypertension may have an abnormal RAAS response to dietary sodium and potassium intake, though this is incompletely described. Our objective was to investigate if plasma renin activity and serum aldosterone are associated with urine sodium and potassium in youth referred for hypertensive disorders.

METHODS

This pilot study was a cross-sectional analysis of baseline data from 44 youth evaluated for hypertensive disorders in a Hypertension Clinic. We recorded urine sodium and potassium concentrations normalized to urine creatinine, plasma renin activity, and serum aldosterone and calculated the sodium/potassium (UNaK) and aldosterone/renin ratios. We used multivariable generalized linear models to estimate the associations of renin and aldosterone with urine sodium and potassium.

RESULTS

Our cohort was diverse (37% non-Hispanic Black, 14% Hispanic), 66% were male, and median age was 15.3 years; 77% had obesity and 9% had a secondary etiology. Aldosterone was associated inversely with urine sodium/creatinine (β: -0.34, 95% CI -0.62 to -0.06) and UNaK (β: -0.09, 95% CI -0.16 to -0.03), and adjusted for estimated glomerular filtration rate and serum potassium.

CONCLUSIONS

Higher serum aldosterone levels, but not plasma renin activity, were associated with lower urine sodium/creatinine and UNaK at baseline in youth referred for hypertensive disorders. Further characterization of the RAAS could help define hypertension phenotypes and guide management. A higher resolution version of the Graphical abstract is available as supplementary information.

Uncommon presentation of primary hyperaldosteronism with severe hypomagnesemia: a Gitelman syndrome mimic

Primary hyperaldosteronism (PA) usually presents with moderate to severe hypertension with or without hypokalemia in adults. However, PA is not commonly associated with severe hypomagnesemia. By contrast, Gitelman syndrome usually presents with clinical manifestations of hypokalemia and hypocalcemia due to hypomagnesemia. Here, we present the case of a 44-year-old woman who first presented with peripheral paresthesia. Her laboratory tests revealed severe hypokalemia, metabolic alkalosis, severe hypomagnesemia, hypocalcemia and secondary hyperparathyroidism. The patient took high dose KCL tablets and Mg tablets to maintain normal values. She took only low-dose hydralazine to maintain normal blood pressure. Further investigations revealed PA with a left adrenal tumor. After left adrenalectomy, she remained in a normotensive, normokalemic and normomagnesemic state without any medical supplements. Thus, PA should be considered in patients with severe hypomagnesemia without moderate to severe hypertension.

Physiological changes in pregnancy

Physiological changes occur in pregnancy to nurture the developing foetus and prepare the mother for labour and delivery. Some of these changes influence normal biochemical values while others may mimic symptoms of medical disease. It is important to differentiate between normal physiological changes and disease pathology. This review highlights the important changes that take place during normal pregnancy.

Salt, aldosterone and extrarenal Na+ - sensitive responses in pregnancy

Outside of pregnancy excessive salt consumption is known to be harmful being linked to increased blood pressure and cardiovascular disease. However, pregnancy represents a major change to a woman's physiology resulting in an intimate adaptation to environmental conditions. It is now becoming apparent that salt is essential for a number of these changes during pregnancy including haematological, cardiac adaptations as well as directly influencing placental development and the uteroplacental immune environment. The present review discusses the important role that salt has during normal pregnancy and evidence will also be presented to show how the placenta may act as a salt sensing organ temporarily, yet substantially regulating maternal blood pressure.

•

The placenta may function as an extrarenal regulator of maternal blood pressure.

•

Na⁺handling in pregnancy is completely different to the non-pregnant situation.

•

Na⁺may actually lower blood pressure in pregnancy affected with pre-eclampsia.

•

Aldosterone is an important regulator of placental and fetal development.

•

Na⁺ may compensate for aldosterone deficiency in pregnancy.

Thiazolidinediones and Edema: Recent Advances in the Pathogenesis of Thiazolidinediones-Induced Renal Sodium Retention

Thiazolidinediones (TZDs) are one of the major classes of antidiabetic drugs that are used widely. TZDs improve insulin resistance by activating peroxisome proliferator-activated receptor gamma (PPARγ) and ameliorate diabetic and other nephropathies, at least, in experimental animals. However, TZDs have side effects, such as edema, congestive heart failure, and bone fracture, and may increase bladder cancer risk. Edema and heart failure, which both probably originate from renal sodium retention, are of great importance because these side effects make it difficult to continue the use of TZDs. However, the pathogenesis of edema remains a matter of controversy. Initially, upregulation of the epithelial sodium channel (ENaC) in the collecting ducts by TZDs was thought to be the primary cause of edema. However, the results of other studies do not support this view. Recent data suggest the involvement of transporters in the proximal tubule, such as sodium-bicarbonate cotransporter and sodium-proton exchanger. Other studies have suggested that sodium-potassium-chloride cotransporter 2 in the thick ascending limb of Henle and aquaporins are also possible targets for TZDs. This paper will discuss the recent advances in the pathogenesis of TZD-induced sodium reabsorption in the renal tubules and edema.

Hormones and hemodynamics in pregnancy

CONTEXT

Normal pregnancy is associated with sodium and water retention, which results in plasma volume expansion prior to placental implantation. The explanation offered for these events is that pregnancy 'resets' both volume and osmoreceptors.

EVIDENCE ACQUISITION

The mechanisms for such an enigmatic 'resetting' in pregnancy have not previously been explained. However, recent human pregnancy studies have demonstrated that the earliest hemodynamic change in pregnancy is primary systemic arterial vasodilation. This arterial underfilling is associated with a secondary increase in cardiac output and activation of the neurohumoral axis, including stimulation of the renin-angiotensin-aldosterone, sympathetic, and non-osmotic vasopressin systems. Resistance to the pressor effects of angiotensin and sympathetic stimulation in pregnancy is compatible with an increase in endothelial nitric oxide synthase activity.

RESULTS

In contrast to the sodium and water retention which occur secondary to the primary arterial vasodilation in cirrhosis, glomerular filtration and renal blood flow are significantly increased in normal pregnancy. A possible explanation for this difference in arterial vasodilation states is that relaxin, an arterial vasodilator which increases during pregnancy, has a potent effect on both systemic and renal circulation. Endothelial damage in pregnancy is pivotal in the pathogenesis of preeclampsia in pregnancy.

CONCLUSIONS

Against a background of the primary arterial vasodilation hypothesis, it is obvious that reversal of the systemic vasodilatation in pregnancy, without subsequent activation of the renin-angiotensin-aldosterone system (78), will evoke a reversal of all the links in the chain of events in normal pregnancy adaptation, thus, it may cause preeclampsia. Namely, a decrease of renal vasodilation will decrease glomerular filtration rate.

Role of renal proximal tubule transport in thiazolidinedione-induced volume expansion

Thiazolidinediones (TZDs), pharmacological activators of peroxisome-proliferator-activated receptors γ (PPARγ), significantly improve insulin resistance and lower plasma glucose concentrations. However, the use of TZDs is associated with plasma volume expansion, the mechanism of which has been a matter of controversy. Originally, PPARγ-mediated enhanced transcription of the epithelial Na channel (ENaC) γ subunit was thought to play a central role in TZD-induced volume expansion. However, later studies suggested that the activation of ENaC alone could not explain TZD-induced volume expansion. We have recently shown that TZDs rapidly stimulate sodium-coupled bicarbonate absorption from renal proximal tubule (PT) in vitro and in vivo. TZD-induced transport stimulation was dependent on PPARγ/Src/EGFR/ERK, and observed in rat, rabbit and human. However, this stimulation was not observed in mouse PTs where Src/EGFR is constitutively activated. Analysis in mouse embryonic fibroblast cells confirmed the existence of PPARγ/Src-dependent non-genomic signaling, which requires the ligand binding ability but not the transcriptional activity of PPARγ. The TZD-induced enhancement of association between PPARγ and Src supports an obligatory role for Src in this signaling. These results support the view that TZD-induced volume expansion is multifactorial. In addition to the PPARγ-dependent enhanced expression of the sodium transport system(s) in distal nephrons, the PPARγ-dependent non-genomic stimulation of renal proximal transport may be also involved in TZD-induced volume expansion.

Hyponatremic hypertensive syndrome in pediatric patients: is it really so rare?

BACKGROUND

Hyponatremic hypertensive syndrome (HHS) is characterized by unilateral renal artery stenosis with secondary hypertension and glomerular and tubular dysfunction due to hyperfiltration and activation of the renin-angiotensin system (RAS).

CASE-DIAGNOSIS/TREATMENT

We describe four children with HHS. All presented with polyuria and polydipsia, electrolyte disturbances, metabolic alkalosis, variable tubular dysfunction, and nephrotic range proteinuria along with hypertension. Interestingly, in one patient, glomerular and tubular abnormalities preceded the development of hypertension. All symptoms resolved after the underlying renal ischemia was corrected by percutaneous angioplasty.

CONCLUSION

Hyponatremic hypertensive syndrome may be more common in children than previously thought. Clinicians should be alert of the signs and symptoms because cure is possible with timely diagnosis and treatment.

Thiazolidinediones enhance sodium-coupled bicarbonate absorption from renal proximal tubules via PPARγ-dependent nongenomic signaling

Thiazolidinediones (TZDs) improve insulin resistance by activating a nuclear hormone receptor, peroxisome proliferator-activated receptor γ (PPARγ). However, the use of TZDs is associated with plasma volume expansion through a mechanism that remains to be clarified. Here we showed that TZDs rapidly stimulate sodium-coupled bicarbonate absorption from the renal proximal tubule in vitro and in vivo. TZD-induced transport stimulation is dependent on PPARγ-Src-EGFR-ERK and observed in rat, rabbit and human, but not in mouse proximal tubules where Src-EGFR is constitutively activated. The existence of PPARγ-Src-dependent nongenomic signaling, which requires the ligand-binding ability, but not the transcriptional activity of PPARγ, is confirmed in mouse embryonic fibroblast cells. The enhancement of the association between PPARγ and Src by TZDs supports an indispensable role of Src in this signaling. These results suggest that the PPARγ-dependent nongenomic stimulation of renal proximal transport is also involved in TZD-induced volume expansion.

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.

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.

Stress reduction and preventing hypertension: preliminary support for a psychoneuroendocrine mechanism

Our objective was to identify endocrine-related mechanisms capable of mediating preventive effects of stress reduction in hypertensive heart disease. Since beneficial effects of stress reduction accrue over time, this cross-sectional, descriptive study sought differences between healthy students not practicing a systematic technique for reducing stress (the average stress, or AS, group, n = 33) and a similar group who for 8.5 years had practiced the Transcendental Meditation (TM) technique, used widely to reduce stress (the low stress, or LS, group, n = 22). The two groups of students, matched for age and area of study, performed timed collections of urine that included (separately) the entire waking and sleeping portions of 1 day. They also completed the Profile of Mood States and the State-Trait Anxiety Inventory, self-report instruments sensitive to subjective level of stress. Urine samples were analyzed for adrenocortical steroids by radioimmunoassay, for Na+, K+, Mg2+, Ca2+, and Zn2+ by atomic absorption spectrometry, and for neurotransmitter metabolites by reverse-phase, high-performance, liquid chromatography, and spectrophotometry. The two groups differed significantly on most measures. Specifically, the LS group was lower in cortisol and aldosterone and higher in dehydroepiandrosterone sulfate (DS) and the serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA). Excretion of sodium, calcium, zinc, and the norepinephrine metabolite, vanillylmandelic acid (VMA), was also lower in this group, as were Na+/K+ ratio, mood disturbance, and anxiety. In women practicing TM, cortisol correlated inversely and DS directly with number of months of TM practice. The results identify improvements in mood state, adrenocortical activity, and kidney function as probable factors in the preventive and treatment effects of stress reduction. Because suboptimal levels of these parameters result from chronic, subjective stress, the findings add mechanistic support to the contention that hypertensive heart disease is avoidable, even in modern industrialized societies.

Hormone-nuclear receptor interactions in health and disease. Mineralocorticoid resistance

Mineralocorticoid resistance, or pseudohypoaldosteronism (PHA), is a rare cause of salt wasting in young children. It may be inherited as an autosomal dominant or recessive trait, it may occur sporadically or, rarely, it may develop secondary to other conditions. It is characterized by episodes of dehydration and hyponatraemia in the face of high aldosterone levels. In most cases, after a short period of salt supplementation no further ill effects are experienced. The condition is of great interest because it provides insights into both the mechanisms by which salt and water balance are controlled and the actions of aldosterone. This article reviews the normal physiology of aldosterone, with particular reference to its biosynthesis and its actions in specific target tissues. Current knowledge regarding the molecular mechanisms involved in aldosterone action is discussed in some detail. The clinical features of PHA are reviewed and diagnostic issues and clinical management considered. Finally, current views regarding the pathophysiology of the condition are presented. Here, considerable uncertainty remains. Whilst in many cases of PHA there is greatly reduced binding of aldosterone to its receptor, the underlying abnormality is yet to be identified; in particular, in spite of strong reasons for suspecting a defect or defects in the mineralocorticoid receptor, there is so far no direct evidence to support this hypothesis. The article concludes with a discussion of other possible explanations for the underlying abnormality in PHA.

Differential effects of ACE inhibitors and vasodilators on renal function curve in patients with primary hypertension

OBJECTIVE

In experimental studies differential effects of antihypertensive agents on the renal function curve have been observed: in SHR captopril lowered the slope of the renal function curve, i.e. blood pressure (BP) became salt sensitive, whereas hydralazine shifted the curve without changing its slope. To evaluate whether ACE inhibitors and vasodilators have different effects on salt sensitivity of BP in humans, we compared the effect of the ACE inhibitor cilazapril and the vasodilator dihydralazine on the renal function curve in a randomized prospective single blind cross-over study.

DESIGN

Nine patients (1 f, 8 m, mean age 41 +/- 4 y) with mild to moderate primary hypertension were put on low (20 mmol/d) and on high salt diet (200 mmol/d). Drugs were given in random low salt+cilazapril, high salt+cilazapril; low salt+dihydralazine, high salt+dihydralazine; or in reverse order.

RESULTS

All antihypertensive interventions lowered BP, but the averaged posttreatment MAP was significantly (p < 0.02) lower with cilazapril on low salt intake (83.6 +/- 2.8 mmHg) than with all of the following: cilazapril on high salt intake (86.4 +/- 2.9 mmHg), dihydralazine on low (91.6 +/- 3.2 mmHg) and high salt (90.1 +/- 3.3 mmHg) intake. Probably as a result of sympathetic activation, average daily heart rate was higher after dihydralazine on low (72.9 +/- 2.9 b/min) and high salt intake (72.4 +/- 2.8 b/min) than after cilazapril on either salt intake (68.7 +/- 3.1 and 62.7 +/- 3.2 b/min).

CONCLUSIONS

The results document that BP reduction after acute ACE inhibition is a function of salt intake, i.e. with ACE inhibitor therapy, BP is "salt sensitive". In contrast, vasodilators of the dihydralazine type have similar antihypertensive effects on low and high salt intake. To the extent that the findings of this short-term study can be extrapolated to long-term effects they suggest that intrarenal mechanisms, i.e. resetting of the pressure-natriuresis relationship, are involved in the long-term antihypertensive action of ACE inhibitors.

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.

Variability of atrial natriuretic peptide plasma levels in ascitic cirrhotics: pathophysiological and clinical implications

Ascitic cirrhotic patients are a heterogenous population with respect to factors that may affect plasma human atrial natriuretic peptide levels (such as degree of plasma volume and plasma levels of angiotensin II, vasopressin and norepinephrine). Thus the proven variability of plasma human atrial natriuretic peptide values in ascitic cirrhotic patients may be due also to the selection of patients, not only to the study conditions. The response to standardized stepped-care medical treatment of ascites makes it possible to characterize ascitic cirrhotic patients with different patterns of renal sodium excretion, intrarenal sodium handling, plasma renin activity, plasma aldosterone and thus, probably, effective circulating volume. Consequently, we evaluated human atrial natriuretic peptide plasma levels in controls (n = 23), in ascitic cirrhotic patients who underwent spontaneous diuresis (group A, n = 7) and in cirrhotic patients who required diuretic treatment (group B, n = 44). The last group was then divided into two subgroups. Subgroup B-R (n = 25) included patients who responded to spironolactone alone, whereas subgroup B-NR (n = 19) included patients who did not respond to 500 mg/day spironolactone. All patients were maintained on identical normocaloric restricted sodium intake (80 mEq/day) throughout the study. Ascitic cirrhotic patients, as a whole, had higher values of human atrial natriuretic peptide than did controls (70.8 +/- 46.6 pg/ml vs. 41.7 +/- 16.3 pg/ml, p < 0.025). No difference was found in human atrial natriuretic peptide/plasma renin activity between the two groups (87 +/- 160 pg/ng/hr vs. 44 +/- 73 pg/ng/hr, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Atrial natriuretic factor: its (patho)physiological significance in humans

The first human studies using relatively high-doses of ANF revealed similar effects as observed in the preceding animal reports, including effects on systemic vasculature (blood pressure fall, decrease in intravascular volume), renal vasculature (rise in GFR, fall in renal blood flow), renal electrolyte excretion (rises in many electrolytes), and changes in release of a number of different hormones. Whether all these changes are the result of direct ANF effects or secondary to a (single) primary event of the hormone remains to be determined. Certainly, it has been proven that more physiological doses of ANF fail to induce short-term changes in many of these parameters leaving only a rise in hematocrit, natriuresis and an inhibition of the RAAS as important detectable ANF effects in humans. This leads us to hypothesize that ANF is a "natriuretic" hormone with physiological significance. The primary function in humans is to regulate sodium homeostasis in response to changes in intravascular volume (cardiac atrial stretch). Induction of excess renal sodium excretion and extracellular volume shift appear to be the effector mechanisms. The exact mechanism of the natriuresis in humans still needs to be resolved. It appears however, that possibly a small rise in GFR, a reduction in proximal and distal tubular sodium reabsorption, as well as an ensuing medullary washout, are of importance. The pathophysiological role of ANF in human disease is unclear. One may find elevated plasma irANF levels and/or decreased responses to exogenous ANF in some disease states. Whether these findings are secondary to the disease state rather than the cause of the disease remains to be resolved. Therapeutic applications for ANF, or drugs that intervene in its production or receptor-binding, seem to be multiple. Most important could be the antihypertensive effect, although areas such as congestive heart failure, renal failure, liver cirrhosis and the nephrotic syndrome cannot be excluded. Although the data that have been gathered to date allowed us to draw some careful conclusions as to the (patho)physiological role of ANF, the exact place of ANF in sodium homeostatic control must still be better defined. To achieve this, we will need more carefully designed low-dose ANF infusion, as well as ANF-breakdown inhibitor studies. Even more promising, however, is the potential area of studies open to us when ANF-receptor (ant)agonists become available for human use.

Study of rat renal brush border membrane vesicles by flow cytometry

The rich heterogeneity of renal tubular membranes and cells continues to provide formidable challenges in the isolation of homogeneous membrane vesicle populations for study. The present study applies flow cytometry, the technique of fluorescence-activated cell sorting, to the study of brush border membrane vesicles. Direct comparison was made of enzymatic marker purity of rat renal cortical brush border membrane vesicles prepared by divalent ion precipitation, or flow cytometry sorting. Flow cytometry sorted membrane vesicles were characterized by greater brush border membrane markers, no detectable mitochondrial or basolateral markers, and greatly reduced Golgi and lysosomal markers. The flow sorted membrane vesicles were functional for transport studies as they took up at least as much 3H-proline and 3H-glucose per mg protein as divalent ion precipitation membrane vesicles. Preparation of membrane vesicles from superficial and deep cortex allowed us to image the different distributions of gamma-glutamyl transferase in membrane vesicles from these areas. Hence, membrane vesicle populations of exceptional purity can be separated according to fluorescent markers using flow cytometry. High speed observations on large numbers of individual vesicles allows identification of subpopulations, and statistical comparison, within a single heterogeneous sample.

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.

Renal medullary circulation: hormonal control

It is now becoming apparent that the medullary circulation in the kidney can be regulated separately from overall renal blood flow. This characteristic of the medullary circulation plays an important role in the kidney's ability to excrete a dilute or concentrated urine in concert with changes in water and sodium transport in the distal nephron secondary to the action of vasopressin, prostaglandins, the renal nerves, and other hormones without significant other renal hemodynamic changes. There is strong evidence that renal autocoids such as angiotensin II and prostaglandins uniquely affect regional blood flow in the inner medulla because of the special structure and organization of the microvasculature in this region. There is also evidence that this regional blood flow is in part regulated by circulating hormones, such as vasopressin and atrial natriuretic peptide, which are released in response to changes in extracellular fluid volume or osmolality. In addition, data are emerging to suggest that the kallikrein-kinin system, acetylcholine, the renal nerves and adenosine participate in this regulation. In addition to the role of the medullary circulation in the urinary concentrating operation, there are data to suggest that the medullary circulation either directly (by changes in physical forces) or indirectly (by regulating medullary toxicity) may influence sodium excretion in a variety of conditions. In this regard, activation of the renin-angiotensin system locally reduces blood flow in the papilla which may be necessary before sodium retention is fully expressed in salt retaining states. Future research looking at the microvasculature of the medulla and papilla and those factors that control the contractility of these vessels are necessary before a clearer picture emerges. Nevertheless, from the data already available it seems reasonable to suggest that the medullary circulation may be as important to kidney function during physiological and pathophysiological states as is the cortical circulation.