α2-Adrenoceptor signaling in cardiomyocytes of spontaneously hypertensive rats starts to impair already at early age

Insight into Cardioprotective Effects and Mechanisms of Dexmedetomidine

PURPOSE

Cardiovascular disease remains the leading cause of death worldwide. Dexmedetomidine is a highly selective α2 adrenergic receptor agonist with sedative, analgesic, anxiolytic, and sympatholytic properties, and several studies have shown its possible protective effects in cardiac injury. The aim of this review is to further elucidate the underlying cardioprotective mechanisms of dexmedetomidine, thus suggesting its potential in the clinical management of cardiac injury.

RESULTS AND CONCLUSION

Our review summarizes the findings related to the involvement of dexmedetomidine in cardiac injury and discusses the results in the light of different mechanisms. We found that numerous mechanisms may contribute to the cardioprotective effects of dexmedetomidine, including the regulation of programmed cell death, autophagy and fibrosis, alleviation of inflammatory response, endothelial dysfunction and microcirculatory derangements, improvement of mitochondrial dysregulation, hemodynamics, and arrhythmias. Dexmedetomidine may play a promising and beneficial role in the treatment of cardiovascular disease.

Cardiac biogenic amine profile and its relationship with parameters of cardiovascular disease in obesity

AIMS

To identify the cardiac biogenic amine profile of obese rats and associate these compounds with parameters of cardiovascular disease.

MAIN METHODS

Wistar rats (n = 20) were randomly distributed into two groups: control and obese. Obesity was induced by a high-sugar fat diet. Biochemical parameters were evaluated. Doppler Echocardiography and systolic blood pressure; interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-α), protein carbonylation, ferric reducing antioxidant power (FRAP), and catalase activity were measured in cardiac tissue. HPLC evaluated the cardiac biogenic profile. Data were compared using the Student's T or Mann-Whitney tests and Spearman's correlation at 5% significance. The principal component analysis (PCA) was performed.

KEY FINDINGS

Obesity generated hypertension, cardiac remodeling and dysfunction, and imbalanced all biochemical, inflammatory, and oxidative markers (p < 0.001). Eight biogenic amines were found in cardiac tissue. Obesity increased serotonin and decreased agmatine, putrescine, cadaverine, and spermidine. Serotonin (r = 0.534 to 0.808) was strong and positively correlated with obesity, biochemical parameters, cardiac inflammation, oxidative stress, hypertension, cardiac remodeling, and dysfunction (p < 0.001). Spermidine (r = -0.560 to -0.680), putrescine (r = -0.532 to -0.805), cadaverine (r = -0.534 to -0.860), and agmatine (r = -0.579 to -0.884) were inversely correlated with the same parameters (p < 0.001). PCA allowed for distinguishing the control and obese groups.

SIGNIFICANCE

There are strong correlations between cardiac biogenic amine levels, cardiac remodeling, and dysfunction resulting from obesity.

CONCLUSION

There is an association between cardiac biogenic amines and cardiovascular disease in obesity. In addition, agmatine, putrescine, cadaverine, and, mainly, serotonin may be new biomarkers for cardiovascular health in obesity and help to improve the diagnosis and treatment of CVD resulting or not from obesity. However, more research is needed to support this conclusion.

Detection and identification of factors in the atrium responsible for blood pressure regulation in patients with hypertension

Resection of the left atrial appendage reportedly improves blood pressure in patients with hypertension. This study aimed to validate the transcriptional profiles of atrial genes responsible for blood pressure regulation in patients with hypertension as well as to identify the molecular mechanisms in rat biological systems. RNA sequencing data of left atrial appendages from patients with (n = 6) and without (n = 6) hypertension were subjected to unsupervised principal component analysis (PCA). Reduction of blood pressure was reflected by third and ninth principal components PC3 and PC9, and that eighteen transcripts, including endothelin-1, were revealed by PCA-based pathway analysis. Resection of the left atrial appendage in hypertensive rats improved their blood pressure accompanied by a decrease in serum endothelin-1 concentration. Expression of the endothelin-1 gene in the atrium and atrial appendectomy could play roles in blood pressure regulation in humans and rats.

α2C-Adrenergic Receptor Blockade Inhibits Langendorff-Isolated Rat Heart Work

We studied the effect of selective α2C-adrenergic receptor antagonist JP-1302 in concentrations of 10-9-10-6 M on inotropy, chronotropy, and coronary flow in the Langendorff-isolated rat heart. JP-1302 in all studied concentrations decreased the left-ventricular myocardium force contraction, HR, and coronary flow. The maximum inotropic, chronotropic, and vascular effects were observed when the antagonist was applied to the perfused solution in a concentration of 10-7 M. The least pronounced decrease in the studied parameters was observed at JP-1302 concentrations of 10-8 and 10-9 M. The obtained data indicate the participation of this subtype of α2-adrenergic receptors in the regulation of activity of isolated adult rats heart.

The Effect of α2-Adrenoreceptors Blockade on the Isolated Rat Heart during the Formation of Sympathetic Innervation

We studied the effects of the α₂-adrenergic receptor antagonist yohimbine (10^-9-10^-6 M) on inotropy, chronotropy, and coronary flow in the Langendorff-isolated heart from 3- and 6-week-old rats. Yohimbine affected all the studied functional parameters of the isolated heart. The force of contraction of the left ventricular myocardium, HR, and coronary flow decreased at all studied concentrations of the antagonist. The maximum chronotropic effect was observed in the heart from 6-week-old rats in the presence of 10^-6 M yohimbine in the perfused solution and in the heart from 3-week-old rats in the presence of 10^-9 M yohimbine. The minimum chronotropic and inotropic effect was recorded in the hearts from 6-week-old animals after application of 10^-9 M α₂-adrenergic receptor blocker and in the hearts from 3-week-old animals at yohimbine concentration of 10^-7 M. The least pronounced decrease in coronary flow in 3- and 6-week-old rats was observed at the minimum concentration of yohimbine.

Adrenergic receptors control frequency-dependent switching of the exocytosis mode between "full-collapse" and "kiss-and-run" in murine motor nerve terminal

AIMS

Neurotransmitter release from the synaptic vesicles can occur through two modes of exocytosis: "full-collapse" or "kiss-and-run". Here we investigated how increasing the nerve activity and pharmacological stimulation of adrenoceptors can influence the mode of exocytosis in the motor nerve terminal.

METHODS

Recording of endplate potentials with intracellular microelectrodes was used to estimate acetylcholine release. A fluorescent dye FM1-43 and its quenching with sulforhodamine 101 were utilized to visualize synaptic vesicle recycling.

KEY FINDINGS

An increase in the frequency of stimulation led to a decrease in the rate of FM1-43 unloading despite the higher number of quanta released. High frequency activity promoted neurotransmitter release via the kiss-and-run mechanism. This was confirmed by experiments utilizing (I) FM1-43 dye quencher, that is able to pass into the synaptic vesicle via fusion pore, and (II) loading of FM1-43 by compensatory endocytosis. Noradrenaline and specific α2-adrenoreceptors agonist, dexmedetomidine, controlled the mode of synaptic vesicle recycling at high frequency activity. Their applications favored neurotransmitter release via full-collapse exocytosis rather than the kiss-and-run pathway.

SIGNIFICANCE

At the diaphragm neuromuscular junctions, neuronal commands are translated into contractions necessary for respiration. During stress, an increase in discharge rate of the phrenic nerve shifts the exocytosis from the full-collapse to the kiss-and-run mode. The stress-related molecule, noradrenaline, restricts neurotransmitter release in response to a high frequency activity, and prevents the shift in the mode of exocytosis through α2-adrenoceptor activation. This may be a component of the mechanism that limits overstimulation of the respiratory system during stress.

Blockade of α2-Adrenergic Receptors Inhibits Functional Parameters of Langendorff-Isolated Rat Heart

We studied the effect of α2-adrenoreceptor antagonist yohimbine in concentrations of 10^-9-10^-6 M on the inotropy, chronotropy, and coronary flow of the Langendorff-isolated rat heart. It was found that antagonist of α2-adrenoreceptors yohimbine changes all the studied parameters of the isolated heart. The force of left ventricular myocardial contraction, HR, and coronary flow decreased after application of all concentrations of α2-adrenoreceptor antagonist. The maximum inotropic, chronotropic, and vascular effects were observed when the antagonist was applied to the perfused solution in a concentration of 10^-9 M. The minimum decrease in coronary flow and HR was observed when yohimbine was applied in a concentration of 10^-8 M; minimum effect on myocardial contractility was revealed at α2-adrenoreceptor blocker concentration of 10^-7 M.

Protein kinase C-mediated calcium signaling as the basis for cardiomyocyte plasticity

Protein kinase C is the superfamily of intracellular effector molecules which control crucial cellular functions. Here, we for the first time did the percentage estimation of all known PKC and PKC-related isozymes at the individual cadiomyocyte level. Broad spectrum of PKC transcripts is expressed in the left ventricular myocytes. In addition to the well-known 'heart-specific' PKCα, cardiomyocytes have the high expression levels of PKCN1, PKCδ, PKCD2, PKCε. In general, we detected all PKC isoforms excluding PKCη. In cardiomyocytes PKC activity tonically regulates voltage-gated Ca²⁺-currents, intracellular Ca²⁺ level and nitric oxide (NO) production. Imidazoline receptor of the first type (I₁R)-mediated induction of the PKC activity positively modulates Ca²⁺ release through ryanodine receptor (RyR), increasing the Ca²⁺ leakage in the cytosol. In cardiomyocytes with the Ca²⁺-overloaded regions of > 9-10 μm size, the local PKC-induced Ca²⁺ signaling is transformed to global accompanied by spontaneous Ca²⁺ waves propagation across the entire cell perimeter. Such switching of Ca²⁺ signaling in cardiac cells can be important for the development of several cardiovascular pathologies and/or myocardial plasticity at the cardiomyocyte level.

Androgen Effects on the Adrenergic System of the Vascular, Airway, and Cardiac Myocytes and Their Relevance in Pathological Processes

INTRODUCTION

Androgen signaling comprises nongenomic and genomic pathways. Nongenomic actions are not related to the binding of the androgen receptor (AR) and occur rapidly. The genomic effects implicate the binding to a cytosolic AR, leading to protein synthesis. Both events are independent of each other. Genomic effects have been associated with different pathologies such as vascular ischemia, hypertension, asthma, and cardiovascular diseases. Catecholamines play a crucial role in regulating vascular smooth muscle (VSM), airway smooth muscle (ASM), and cardiac muscle (CM) function and tone.

OBJECTIVE

The aim of this review is an updated analysis of the role of androgens in the adrenergic system of vascular, airway, and cardiac myocytes. Body. Testosterone (T) favors vasoconstriction, and its concentration fluctuation during life stages can affect the vascular tone and might contribute to the development of hypertension. In the VSM, T increases α1-adrenergic receptors (α ₁-ARs) and decreases adenylyl cyclase expression, favoring high blood pressure and hypertension. Androgens have also been associated with asthma. During puberty, girls are more susceptible to present asthma symptoms than boys because of the increment in the plasmatic concentrations of T in young men. In the ASM, β ₂-ARs are responsible for the bronchodilator effect, and T augments the expression of β ₂-ARs evoking an increase in the relaxing response to salbutamol. The levels of T are also associated with an increment in atherosclerosis and cardiovascular risk. In the CM, activation of α _1A-ARs and β ₂-ARs increases the ionotropic activity, leading to the development of contraction, and T upregulates the expression of both receptors and improves the myocardial performance.

CONCLUSIONS

Androgens play an essential role in the adrenergic system of vascular, airway, and cardiac myocytes, favoring either a state of health or disease. While the use of androgens as a therapeutic tool for treating asthma symptoms or heart disease is proposed, the vascular system is warmly affected.