Hyponatremia: mechanisms and newer treatments

Severe hyponatremia in children: a review of the literature through instructive cases

Hyponatremia is the most common electrolyte disorder in the pediatric population. Symptoms are related to the time in which hyponatremia has developed. The acute presentation could be dramatic, with neurological symptoms like headache, seizure, impaired mental status and even coma. It is essential for the physician to be aware of the possible causes of hyponatremia in the child in order to start a prompt treatment.

Vasopressin Receptor Antagonists for the Correction of Hyponatremia in Chronic Heart Failure: An Underutilized Therapeutic Option in Current Clinical Practice?

In the congestive heart failure (CHF) setting, chronic hyponatremia is very common. The present review aims at addressing topics relevant to the pathophysiology of hyponatremia in the course of CHF as well as its optimal treatment, including the main advantages and the limitations resulting from the use of the available dietary and pharmacological measures approved for the treatment of this electrolytic trouble. A narrative review is carried out in order to represent the main modalities of therapy for chronic hyponatremia that frequently complicates CHF. The limits of usual therapies implemented for CHF-related chronic hyponatremia are outlined, while an original analysis of the main advancements achieved with the use of vasopressin receptor antagonists (VRAs) is also executed. The European regulatory restrictions that currently limit the use of VRAs in the management of CHF are substantially caused by financial concerns, i.e., the high costs of VRA therapy. A thoughtful reworking of current restrictions would be warranted in order to enable VRAs to be usefully associated to loop diuretics for decongestive treatment of CHF patients with hyponatremia.

Vasopressin receptor antagonists in patients with chronic heart failure

In this brief review, the pathophysiology of hyponatremia and its clinical significance in the course of chronic heart failure (CHF) are illustrated. Moreover, issues concerning the optimal treatment for hyponatremia during CHF are addressed and discussed. In addition, advantages and limitations resulting from the use of vasopressin receptor antagonists, drugs that have recently emerged as the best available resource against hyponatremia, are highlighted.

The 2.1 Å resolution structure of cyanopindolol-bound β1-adrenoceptor identifies an intramembrane Na+ ion that stabilises the ligand-free receptor

The β₁-adrenoceptor (β₁AR) is a G protein-coupled receptor (GPCR) that is activated by the endogenous agonists adrenaline and noradrenaline. We have determined the structure of an ultra-thermostable β₁AR mutant bound to the weak partial agonist cyanopindolol to 2.1 Å resolution. High-quality crystals (100 μm plates) were grown in lipidic cubic phase without the assistance of a T4 lysozyme or BRIL fusion in cytoplasmic loop 3, which is commonly employed for GPCR crystallisation. An intramembrane Na⁺ ion was identified co-ordinated to Asp87^2.50, Ser128^3.39 and 3 water molecules, which is part of a more extensive network of water molecules in a cavity formed between transmembrane helices 1, 2, 3, 6 and 7. Remarkably, this water network and Na⁺ ion is highly conserved between β₁AR and the adenosine A_2A receptor (rmsd of 0.3 Å), despite an overall rmsd of 2.4 Å for all Cα atoms and only 23% amino acid identity in the transmembrane regions. The affinity of agonist binding and nanobody Nb80 binding to β₁AR is unaffected by Na⁺ ions, but the stability of the receptor is decreased by 7.5°C in the absence of Na⁺. Mutation of amino acid side chains that are involved in the co-ordination of either Na⁺ or water molecules in the network decreases the stability of β₁AR by 5–10°C. The data suggest that the intramembrane Na⁺ and associated water network stabilise the ligand-free state of β₁AR, but still permits the receptor to form the activated state which involves the collapse of the Na⁺ binding pocket on agonist binding.

Pathophysiology of lower extremity edema in acute heart failure revisited

BACKGROUND

The pathophysiology and key determinants of lower extremity edema in patients with acute heart failure are poorly investigated.

METHODS

We prospectively enrolled 279 unselected patients presenting to the Emergency Department with acute heart failure. Lower extremity edema was quantified at predefined locations. Left ventricular ejection fraction, central venous pressure quantifying right ventricular failure, biomarkers to quantify hemodynamic cardiac stress (B-type natriuretic peptide), and the activity of the arginine-vasopressin system (copeptin) also were recorded.

RESULTS

Lower extremity edema was present in 218 (78%) patients and limited to the ankle in 22%, reaching the lower leg in 40%, reaching the upper leg in 11%, and was generalized (anasarca) in 3% of patients. Patients in the 4 strata according to the presence and extent of lower leg edema had comparable systolic blood pressure, left ventricular ejection fraction, central venous pressure, and B-type natriuretic peptide levels, as well as copeptin and glomerular filtration rate (P=NS for all). The duration of dyspnea preceding the presentation was longer in patients with more extensive edema (P=.006), while serum sodium (P=.02) and serum albumin (P=.03) was lower.

CONCLUSION

Central venous pressure, hemodynamic cardiac stress, left ventricular ejection fraction, and the activity of the arginine-vasopressin system do not seem to be key determinants of the presence or extent of lower extremity edema in acute heart failure.