Atrial natriuretic peptide (ANP) as a neuropeptide: interaction with angiotensin II on volume control and renal sodium handling

Long Term Impact of Epicardial Left Atrial Appendage Ligation on Systemic Hemostasis: LAA HOMEOSTASIS-2

Background: Recent data suggest that epicardial left atrial appendage closure (LAAC) is associated with several short-term neurohormonal effects. However, the long-term effects are currently unknown. Objective: To investigate the effects of percutaneous epicardial left atial appendage (LAA) exclusion using LARIAT on neurohormonal profiles at long-term follow-up. Methods: In a prospective single centre study, 60 patients with long-standing, persistent atrial fibrillation (AF) LARIAT were treated. The major hormones of the adrenergic system, renin-angiotensin-aldosterone system (RAAS), and natriuretic peptides were assessed before the intervention and at regular intervals during the following two years. Results: In patients with epicardial LAAC, atrial natriuretic peptide (ANP) levels were significantly increased from baseline at 24 h and decreased at 7 days, 1 month, and 3 months, while remaining unchanged at 12 and 24 months. Noradrenaline levels were significantly lower at 24 h, 7 days, 1 month, 6 months, 12 months, and 24 months, while epinephrine levels decreased significantly at 1 month, 6 months, 12 months, and 24 months. Plasma renin activity significantly decreased at 7 days, 1 month, 6 months, 12 months, and 24 months, while aldosterone levels significantly decreased at 6 months, 12 months, and 24 months. Endothelin-1 and vasopressin showed a significant increase and decrease, respectively, at 24 h, 7 days, 1 month, 6 months, 12 months, and 24 months. There was also a significant decrease in systolic and diastolic blood pressure at 3 months, 6 months, 1 year, and 2 years after the intervention. Conclusions: Epicardial LAAC in AF patients is associated with persistent neurohormonal changes favouring blood pressure reduction.

Dexamethasone-induced diuresis is associated with inhibition of the renin-angiotensin-aldosterone system in rats

In heart failure (HF) patients, diuretics remain the cornerstone of therapy to relieve fluid retention. However, the resulting volume loss activates the renin-angiotensin-aldosterone system (RAAS), which blunts the decline in volume depletion and blood pressure. RAAS activation, in turn, compromises the diuretic decongesting effect. Although corticosteroids can induce potent diuresis in HF patients, the effects of corticosteroids on RAAS activation remain unclear. Therefore, we assessed the effects of dexamethasone (Dex) on urine output and plasma angiotensin II and aldosterone levels in rats following water deprivation-induced dehydration, following induction of chronic HF (CHF), and following induction of CHF and volume expansion therapy. In the dehydration model, Dex significantly increased urine output and inhibited dehydration-induced RAAS activation. This favorable effect was abolished by the glucocorticoid receptor antagonist RU486, suggesting involvement of the glucocorticoid receptor. In the CHF model, Dex treatments doubled urine output without activating RAAS. Moreover, in acute volume expansion experiments, Dex pretreatments led to potent diuresis during the pretreatment period and restored renal adaptation to acute volume expansion without activating RAAS in rats with CHF. Collectively, these data show that corticosteroids induce potent diuresis without activating RAAS in rats.

Review: DNA methylation and alcohol use disorders: Progress and challenges

BACKGROUND AND OBJECTIVES

Risk for alcohol use disorders (AUDs) is influenced by gene-environment interactions. Environmental factors can affect gene expression through epigenetic mechanisms such as DNA methylation. This review outlines the findings regarding the association of DNA methylation and AUDs.

METHODS

We searched PubMed (by April 2016) and identified 29 studies that examined the association of DNA methylation and AUDs. We also evaluated the methods used in these studies.

RESULTS

Two studies demonstrated elevated global (repetitive element) DNA methylation levels in AUD subjects. Fifteen candidate gene studies showed hypermethylation of promoter regions of six genes (AVP, DNMT3B, HERP, HTR3A, OPRM1, and SNCA) or hypomethylation of the GDAP1 promoter region in AUD subjects. Five genome-wide DNA methylation studies demonstrated widespread DNA methylation changes across the genome in AUD subjects. Six studies showed significant correlations of DNA methylation with gene expression in AUD subjects. Three studies revealed interactive effects of genetic variation and DNA methylation on susceptibility to AUDs. Most studies analyzed AUD-associated DNA methylation changes in the peripheral blood; a few studies examined DNA methylation changes in postmortem brains of AUD subjects.

DISCUSSION AND CONCLUSIONS

Chronic alcohol consumption may result in DNA methylation changes, leading to neuroadaptations that may underlie some of the mechanisms of AUD risk and persistence. Future studies are needed to confirm the few existing results, and then to elucidate whether DNA methylation changes are the cause or consequence of AUDs.

SCIENTIFIC SIGNIFICANCE

DNA methylation profiles may be used to assess AUD status or monitor AUD treatment response. (Am J Addict 2017;26:502-515).

Action of C-type natriuretic peptide (CNP) on passive avoidance learning in rats: involvement of transmitters

The action of C-type of natriuretic peptide (CNP) was tested on one-way passive avoidance learning in rats. The involvement of transmitters was investigated by pretreating the animals with different receptor blockers. CNP administered into the lateral brain ventricle caused a dose-dependent facilitation of learning and consolidation of passive avoidance learning, but was ineffective on retrieval. Pretreatment of the animals with atropine, haloperidol or the nitric oxide synthase inhibitor nitro-L-arginine abolished the action of CNP. Phenoxybenzamine, naloxone, bicuculline, propranolol and methysergide were ineffective in modifying the action of CNP on consolidation. The results suggest that CNP is able to improve the learning and consolidation of learning in a passive avoidance paradigm, but is ineffective on retrieval processes. In the action of CNP, dopamine, acetylcholine and nitric oxide could be the mediating transmitters.

Angiotensin as neuromodulator/neurotransmitter in central control of body fluid and electrolyte homeostasis

Stimulation of central angiotensin receptors promotes, among others, drinking behaviour, stimulation of natriuresis and increased release of vasopressin. Angiotensin (ANG II)-containing pathways in the lamina terminalis and the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei, brain areas involved in the regulation of body fluid homeostasis, have been described. All these areas express predominantly AT1 receptors. The drinking response and the vasopressin release to centrally administered ANG II are mediated by AT1 receptors, while AT2 receptors exert inhibitory effects. Evidence for the involvement of the catecholaminergic and angiotensinergic pathways in the PVN and SON in mediating the ANG II-induced release of vasopressin is presented. ANG II is released in the PVN upon local osmotic stimulation and water deprivation. Finally, we present evidence that activation of central angiotensinergic receptors, water deprivation, or hypertonicity induce transcription of immediate-early genes and expression of the respective proteins in the lamina terminalis and in the PVN and SON. The summarized data implicate ANG II as a neuromodulator/neurotransmitter in central control of body fluid and electrolyte homeostasis.

Inefficiency of intracerebroventricular ANP to alter haemodynamic, plasma vasopressin and renin responses to haemorrhage in sheep

Whether intracerebroventricular (i.c.v.) infusion of atrial natriuretic peptide (human-ANP, 1-28) 25 pmol min-1 influences the tolerance to blood loss and haemorrhage induced cardiovascular, vasopressin and renin responses were studied in five conscious sheep. The i.c.v. infusion was started 60 min prior to a slow (0.7 ml kg-1 min-1) venous haemorrhage, was run concurrently with bleeding, and for 90 min thereafter. Venous blood was removed until the mean systemic arterial pressure suddenly fell to about 50 mmHg. There were no statistically significant differences in either the bleeding volume necessary to induce the sudden decrease in blood pressure, or in cardiovascular parameters measured by venous heart thermodilution catheterization, compared with control experiments with i.c.v. infusion of artificial CSF. The plasma protein and vasopressin concentrations and renin activity were unaffected by the i.c.v. infusion of ANP as were the changes in these parameters occurring during the subsequent haemorrhage. The same negative findings were obtained with a three times higher dose of ANP(1-28) (75 pmol min-1), tested in three of the animals. Thus the i.c.v. infusion of ANP(1-28), in amounts expected to elevate the CSF concentration far above basal levels does apparently not influence normal blood pressure regulation or alter haemodynamic, vasopressin and renin responses to haemorrhage in conscious sheep.