Altered regulation of renal nitric oxide, atrial natriuretic peptide and cyclooxygenase systems in aldosterone escape in rats

Dietary sodium alters aldosterone's effect on renal sodium transporter expression and distal convoluted tubule remodelling

Aldosterone is responsible for maintaining volume and potassium homeostasis. Although high salt consumption should suppress aldosterone production, individuals with hyperaldosteronism lose this regulation, leading to a state of high aldosterone despite dietary sodium consumption. The present study examines the effects of elevated aldosterone, with or without high salt consumption, on the expression of key Na+ transporters and remodelling in the distal nephron. Epithelial sodium channel (ENaC) α-subunit expression was increased with aldosterone regardless of Na+ intake. However, ENaC β- and γ-subunits unexpectedly increased at both a transcript and protein level with aldosterone when high salt was present. Expression of total and phosphorylated Na+ Cl- cotransporter (NCC) significantly increased with aldosterone, in association with decreased blood [K+ ], but the addition of high salt markedly attenuated the aldosterone-dependent NCC increase, despite equally severe hypokalaemia. We hypothesized this was a result of differences in distal convoluted tubule length when salt was given with aldosterone. Imaging and measurement of the entire pNCC-positive tubule revealed that aldosterone alone caused a shortening of this segment, although the tubule had a larger cross-sectional diameter. This was not true when salt was given with aldosterone because the combination was associated with a lengthening of the tubule in addition to increased diameter, suggesting that differences in the pNCC-positive area are not responsible for differences in NCC expression. Together, our results suggest the actions of aldosterone, and the subsequent changes related to hypokalaemia, are altered in the presence of high dietary Na+ . KEY POINTS: Aldosterone regulates volume and potassium homeostasis through effects on transporters in the kidney; its production can be dysregulated, preventing its suppression by high dietary sodium intake. Here, we examined how chronic high sodium consumption affects aldosterone's regulation of sodium transporters in the distal nephron. Our results suggest that high sodium consumption with aldosterone is associated with increased expression of all three epithelial sodium channel subunits, rather than just the alpha subunit. Aldosterone and its associated decrease in blood [K+ ] lead to an increased expression of Na-Cl cotransporter (NCC); the addition of high sodium consumption with aldosterone partially attenuates this NCC expression, despite similarly low blood [K+ ]. Upstream kinase regulators and tubule remodelling do not explain these results.

The emerging role of aldosterone/mineralocorticoid receptors in the pathogenesis of erectile dysfunction

PURPOSE

Aldosterone is an old hormone that has been discovered for more than fifty years. The clinical application of its receptors' inhibitors, especially spirolactone, has benifited patients for decades worldwide. In this review, we briefly summarized the molecular mechanism of aldosterone/mineralocorticoid receptors (Ald-MRs) signaling in cardiovascular diseases and its emerging role in erectile dysfunction.

METHODS

We searched PubMed, Web of Science, and Scopus for manuscripts published prior to December 2017 using key words " aldosterone " AND " erectile dysfunction " OR " cardiovascular disease " OR " mineralocorticoid receptors ". Related literature and clinical perspectives were collated, summarized and discussed in this review.

RESULTS

The increase of reactive oxygen species production, inhibition of endothelial nitric oxide synthase system, and induction of inflammation are ubiquitous in vascular endothelial cells or vascular smooth muscle cells after the activation of Ald-MRs pathway. In addition, in cardiovascular diseases with over-active Ald-MRs signaling, MRs blockade could reverse the injury and improve the prognosis. Notably, multiple studies have correlated aldosterone and MRs to the pathogenesis of erectile function, while the mechanism is largely unperfectly identified.

CONCLUSION

In conclusion, we summarize the current evidence to highlight the potential role of aldosterone in erectile dysfunction and provide critical insights into the treatment of the disease.

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.