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

Nocturia and obstructive sleep apnoea

Nocturia, the need to urinate at night, is a common symptom in patients with obstructive sleep apnoea (OSA). Continuous positive airway pressure treatment can reduce nocturia in some patients, but the underlying mechanisms are complex and not fully understood. OSA affects the autonomic nervous system, oxidative stress and endothelial damage. Furthermore, the commonly held theory attributing polyuria to a false signal of cardiac overload and response natriuresis has limitations. A comprehensive approach to the management of nocturia in OSA, considering factors such as comorbidities, medication use, alcohol consumption and lifestyle, is needed. Effective management of nocturia in OSA requires a multidisciplinary approach, and urologists should be aware of the potential effect of OSA on physiology and refer patients for further testing at a sleep centre. In addition to continuous positive airway pressure, other interventions such as oral appliances and surgical obstruction treatment could be beneficial for some patients. Overall, understanding the complex interplay between OSA and nocturia is crucial for optimizing patient outcomes.

Transcriptome Analysis Reveals Biosynthesis of Important Bioactive Constituents and Mechanism of Stem Formation of Dendrobium huoshanense

The stem of Dendrobium huoshanense C.Z. Tang and S.J. Cheng was widely used as a medicinal herb in health care products due to its broad pharmacological activities. However, the molecular regulation mechanism of stem development and biosynthetic pathways of important bioactive substances are still unclear in D. huoshanense. In this study, the bioactive compounds in leaves, stems and roots, and the identification of candidate genes involved in stem formation and biosynthesis of active compounds via transcriptome sequence were analyzed. The accumulation of total polysaccharides and flavonoids were varied significantly in different tissues. A comparative transcriptomic analysis revealed several differentially expressed genes (DEGs) involved in polysaccharides biosynthesis (103 genes), including fructose and mannose related genes (29 genes) and glycosyltransferase genes (74 genes), and flavonoids biosynthesis (15 genes). Some candidate genes that participated in photoperiod regulation (27 genes), starch and sucrose metabolism (46 genes), and hormone-induced activation of signaling pathways (38 genes) may be involved in stem formation. In sum, this study provides a foundation for investigating the molecular processes in the biosynthesis of active compounds and stem development. The transcriptome data presented here provides an important resource for the future studies of the molecular genetics and functional genomics in D. huoshanense and optimized control of the active compounds produced by D. huoshanense.

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.

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.

Is aldosterone the missing link in refractory hypertension?: aldosterone-to-renin ratio as a marker of inappropriate aldosterone activity

Use of the random aldosterone-to-renin ratio (ARR) as a reliable marker of inappropriate aldosterone activity has led to primary aldosteronism (PA) being increasingly diagnosed in hypertensive patients. At least 10% of hypertensives have been found to have PA, the majority of whom presumably have bilateral adrenal hyperplasia or idiopathic hyperaldosteronism as an aetiology for PA. Whilst these patients clearly have excess aldosterone activity, they have in common many features that are found in hypertensive patients in general, amongst which include heightened angiotensin II adrenal sensitivity. Whether these individuals belong within the spectrum of 'essential hypertension' is being debated, but is probably irrelevant clinically since they appear to respond favourably to spironolactone treatment. In addition, there is recent evidence suggesting that these patients overexpress a key enzyme involved in aldosterone production, the aldosterone synthase, the activity of which appears to relate to its genotypic variation.

Atrial natriuretic factor significantly contributes to the mineralocorticoid escape phenomenon. Evidence for a guanylate cyclase-mediated pathway

The mechanism underlying the mineralocorticoid escape phenomenon remains unknown. To assess the possible contribution of natriuretic peptides to mineralocorticoid escape, rats were injected with 5 mg deoxycorticosterone acetate for 3 d. Plasma atrial natriuretic factor (ANF) rose to twice basal levels and atrial ANF content decreased significantly by 24 h of treatment. This coincided with renal escape and with a significant increase in urinary cGMP excretion. Plasma ANF remained elevated and atrial ANF content continued to decline by 48 and 72 h while atrial ANF mRNA levels increased significantly only at 72 h. Plasma brain natriuretic peptide did not increase during escape although atrial brain natriuretic peptide mRNA levels increased significantly. Chronically administered HS-142-1 (HS), a specific antagonist of the guanylate cyclase-coupled natriuretic peptide receptors, significantly and dose-dependently impaired the escape phenomenon. The highest dose of HS completely suppressed the increase in urinary cGMP. Despite the continued suppression, partial escape was observed by the end of the observation period. HS alone influenced neither plasma nor tissue or urine parameters. These findings show that despite activation of atrial ANF, blockade of the guanylate cyclase-coupled natriuretic peptide receptors impairs the ability of the kidney to escape the Na+ retaining effect of excess mineralocorticoid in a dose-dependent fashion. Later-acting, unknown mechanisms eventually come into play to mediate the escape phenomenon through a guanylate cyclase-independent pathway. Therefore, ANF of cardiac origin appears to be a major factor initiating mineralocorticoid escape through a guanylate cyclase-dependent pathway.

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.

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.

Effects of atrial natriuretic peptide on distal tubule function in humans

To characterize the actions of atrial natriuretic peptide (ANP) in the human distal nephron, we studied interactions between ANP (0.02 micrograms/kg.min i.v.) and acutely administered substances acting in the distal nephron, that is, amiloride and aldosterone, in six healthy humans during maximal water diuresis. ANP increased NaCl excretion, fractional lithium excretion (FELi) and decreased diluting segment reabsorption estimated from free water clearance. Amiloride increased natriuresis, had no effect on FELi, but decreased diluting segment reabsorption. Aldosterone had the opposite effect. When infused in addition to amiloride, ANP still increased NaCl excretion, the changes in sodium handling parameters being comparable to those seen after ANP alone. Amiloride did not increase the further natriuretic response to ANP. These findings suggest that ANP increases distal sodium delivery, and decreases sodium reabsorption in distal segments by a mechanism also sensitive to amiloride. ANP abolished much of the antinatriuretic effect of aldosterone, which may also be explained by assuming a partial overlap of the target segments of ANP and aldosterone in the distal nephron. Remarkably, in neither of these experiments was the natriuresis after ANP accompanied by a kaliuresis, for which the explanation remains obscure.

Blunted natriuretic response and low blood pressure after atrial natriuretic factor in early cirrhosis

We compared the natriuretic response to a standard dose of atrial natriuretic factor in nine patients with early cirrhosis (no ascites or edema) with the response in normal subjects displaying a range of baseline sodium excretions due to different sodium intakes (20 mmoles per day, n = 9; 100 mmoles per day, n = 9, and 200 mmoles per day, n = 9). In these normal subjects, sodium output rose, in the same order, from 49 +/- 12 to 177 +/- 26, from 116 +/- 21 to 365 +/- 106 and from 228 +/- 29 to 901 +/- 85 mumoles per min in the first 20 min after 100 micrograms atrial natriuretic factor (human atrial natriuretic factor 99-126). Thus, irrespective of basal excretion, natriuresis rose by at least 2-fold. In the cirrhotic patients, natriuresis rose from 173 +/- 42 to 305 +/- 77 mumoles per min, that is by hardly 1-fold, significantly less than in the normal subjects (p less than 0.01). Renal function studies indicated that atrial natriuretic factor caused less rise in glomerular filtration rate and in fractional sodium excretion. Atrial natriuretic factor induced a fall in blood pressure only in the cirrhotic group, from 130 +/- 4/81 +/- 2 to 108 +/- 4/68 +/- 3 mmHg (p less than 0.001). Plasma atrial natriuretic factor was not low in the cirrhotic patients. Although these data are compatible with a primary disturbance of sodium excretion in early cirrhosis without ascites, such an explanation is complicated by the concomitant drop in blood pressure after atrial natriuretic factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Opposite effects of enalapril and nitrendipine on natriuretic response to atrial natriuretic factor. Renal function evaluated with clearance studies in humans

In clearance studies, we analyzed the effect of Ca2+ entry blockade with nitrendipine treatment (20 mg b.i.d. for 4 days) and of converting enzyme inhibition with enalapril treatment (20 mg b.i.d. for 4 days) on renal response to atrial natriuretic factor (ANF) (25 micrograms bolus followed by an infusion of 0.03 microgram/kg/min for 90 minutes) in six healthy volunteers who were taking 300 mmol sodium daily. In a control study ANF was administered without Ca2+ entry blockade or converting enzyme inhibition. Natriuresis rose from 239 +/- 38 to 605 +/- 137 mumol/min in the control study (p less than 0.05), from 330 +/- 53 to 943 +/- 152 mumol/min with Ca2+ entry blockade (p less than 0.05), and from 236 +/- 22 to 344 +/- 39 mumol/min with converting enzyme inhibition (NS). ANF induced a rise in maximal free water clearance, inulin clearance, and in the excretion of multiple electrolytes except potassium. Fractional lithium reabsorption fell. In general, these effects were stronger during Ca2+ entry blockade and blunted during converting enzyme inhibition. p-Aminohippurate clearance tended to decrease during the control study (NS), remained constant during Ca2+ entry blockade, and decreased significantly when ANF was infused during converting enzyme inhibition (p less than 0.05 vs. control and vs. Ca2+ entry blockade study). Blood pressure was lowered by Ca2+ entry blockade and, to a somewhat greater extent, by converting enzyme inhibition, but ANF administration induced no additional fall except for a short-term drop during Ca2+ entry blockade.(ABSTRACT TRUNCATED AT 250 WORDS)