Mechanisms of noradrenaline release in the anoxic heart of the rat

Nandrolone Plus Moderate Exercise Increases the Susceptibility to Lethal Arrhythmias

Background:

Until now, no experimental study has directly assessed the arrhythmogenesis of chronic consumption of anabolic androgenic steroids along with moderate-intensity endurance exercise.

Objectives:

We evaluated the influence of integration of anabolic androgenic steroids along with moderate-intensity endurance exercise on susceptibility to lethal ventricular arrhythmias in rat.

Materials and Methods:

The animal groups were as follows: control group (CTL); exercise group (EX) which were under 6 weeks of treadmill exercise; nandrolone group (Nan) which received 5 mg/kg of nandrolone decanoate twice a week; vehicle group (Arach) which received Arachis oil (solvent of nandrolone); trained vehicle group (Arach + Ex); and trained nandrolone group (Nan + Ex). One day after ending of the intervention period, arrhythmia was inducted by intravenous infusion of aconitine and ventricular arrhythmias were recorded. Then malondialdehyde (MDA) and glutathione peroxidase (GPX) of heart tissue were measured.

Results:

Nandrolone, exercise, and their combination were associated with heart hypertrophy. Exercise could prevent the incremental effect of nandrolone on MDA/GPX ratio. Chronic administration of nandrolone with moderate-intensity endurance exercise had no significant effect on blood pressure, heart rate, and basal electrocardiographic parameters. Combination of nandrolone and exercise significantly increased the incidence of ventricular fibrillation (VF) and reduced the VF latency (P < 0.05).

Conclusions:

The findings suggest that chronic coadministration of nandrolone with moderate-intensity endurance exercise facilitates the VF occurrence in rat. Complementary studies are needed to elucidate the involved mechanisms of this abnormality.

Anabolic Androgenic Steroid (AAS) related deaths: autoptic, histopathological and toxicological findings

Anabolic androgenic steroids (AASs) represent a large group of synthetic derivatives of testosterone, produced to maximize anabolic effects and minimize the androgenic ones. AAS can be administered orally, parenterally by intramuscular injection and transdermally. Androgens act by binding to the nuclear androgen receptor (AR) in the cytoplasm and then translocate into the nucleus. This binding results in sequential conformational changes of the receptor affecting the interaction between receptor and protein, and receptor and DNA. Skeletal muscle can be considered as the main target tissue for the anabolic effects of AAS, which are mediated by ARs which after exposure to AASs are up-regulated and their number increases with body building. Therefore, AASs determine an increase in muscle size as a consequence of a dose-dependent hypertrophy resulting in an increase of the cross-sectional areas of both type I and type II muscle fibers and myonuclear domains. Moreover, it has been reported that AASs can increase tolerance to exercise by making the muscles more capable to overload therefore shielding them from muscle fiber damage and improving the level of protein synthesis during recovery. Despite some therapeutic use of AASs, there is also wide abuse among athletes especially bodybuilders in order to improve their performances and to increase muscle growth and lean body mass, taking into account the significant anabolic effects of these drugs. The prolonged misuse and abuse of AASs can determine several adverse effects, some of which may be even fatal especially on the cardiovascular system because they may increase the risk of sudden cardiac death (SCD), myocardial infarction, altered serum lipoproteins, and cardiac hypertrophy. The aim of this review is to focus on deaths related to AAS abuse, trying to evaluate the autoptic, histopathological and toxicological findings in order to investigate the pathophysiological mechanism that underlines this type of death, which is still obscure in several aspects. The review of the literature allowed us to identify 19 fatal cases between 1990 and 2012, in which the autopsy excluded in all cases, extracardiac causes of death.

Nandrolone Potentiates Arrhythmogenic Effects of Cardiac Ischemia in the Rat

Anabolic steroid abuse has been associated with thrombosis and arteriosclerosis, both of which predispose to myocardial ischemia and infarction. However, there are reports of sudden cardiac death in the absence of thrombus and atheroma following anabolic steroid use. Although treatment with the commonly abused steroid, nandrolone, has been shown to decrease recovery of systolic function following ischemia in isolated rat hearts, it is unknown whether anabolic steroids can increase the incidence of fatal arrhythmia associated with cardiac ischemia. Anesthetized male Sprague-Dawley rats were administered vehicle or nandrolone (10-160 microg/kg/min iv) 10 min prior to 15-min occlusion of the left anterior descending coronary artery followed by 10-min reperfusion. Nandrolone, in this dose range, did not significantly change heart rate, blood pressure, or cardiac rhythm in the absence of ischemia. However, the fraction of rats surviving ischemia was significantly (p < 0.05) decreased by nandrolone at both 40 and 160 microg/kg/min, while survival time during ischemia was decreased significantly (p < 0.001) by nandrolone 160 microg/kg/min. An increase (p < 0.05) in the duration of ventricular fibrillation was noted at the highest compared to the lowest dose of nandrolone, corresponding to a significant increase in the fraction of rats experiencing ventricular fibrillation (p < 0.01). Nandrolone had no effect on the frequency or duration of ventricular fibrillation or survival time during reperfusion. Although the mechanisms underlying these effects are currently unclear, they indicate that exposure to anabolic steroids in combination with transient reductions in coronary blood flow may explain some reports of sudden cardiac death in anabolic steroid users.

Differential effects of acidosis, high potassium concentrations, and metabolic inhibition on noradrenaline release and its presynaptic muscarinic regulation

It was the aim of the present study to characterize the effect of single components of ischaemia, such as inhibition of aerobic and anaerobic energy production by combined anoxic and glucose-free perfusion (metabolic inhibition), high extracellular potassium concentrations (hyperkalaemia), and acidosis, on (1). the stimulated release of noradrenaline from the in situ perfused guinea-pig heart and (2). its presynaptic modulation by the muscarinic agonist carbachol. The release of endogenous noradrenaline from efferent cardiac sympathetic nerve endings was induced by electrical stimulation of the left stellate ganglion (1 min, 5 V, 12 Hz) and quantified in the coronary venous effluent by high-performance liquid chromatography. Under control conditions, two consecutive electrical stimulations (S1, S2) elicited a similar noradrenaline overflow (S2/S1: 0.98 plus minus 0.05). After 10 min of global myocardial ischaemia overflow of endogenous noradrenaline was significantly reduced (S2/S1: 0.18 plus minus 0.03; P< 0.05). When studied separately, metabolic inhibition, hyperkalaemia (16 mM), and acidosis (pH 6.0) each markedly attenuated stimulated noradrenaline overflow (S2/S1: 0.65 plus minus 0.05, 0.43 plus minus 0.14, and 0.37 plus minus 0.09, respectively; P< 0.05). The muscarinic agonist carbachol (10 microM) inhibited stimulated noradrenaline release under normoxic conditions (S2/S1: 0.41 plus minus 0.07; P< 0.05). However, after 10 min of global myocardial ischaemia the inhibitory effect of carbachol on noradrenaline overflow was completely lost. Single components of ischaemia had a differential effect on presynaptic muscarinic modulation. Whereas hyperkalaemia (8-16 mM) did not affect muscarinic inhibition of noradrenaline release, carbachol lost its inhibitory effect during acidosis and metabolic inhibition. In conclusion, hyperkalaemia, metabolic inhibition, and severe acidosis each contribute to reduced overflow of noradrenaline after 10 min of myocardial ischaemia. However, presynaptic muscarinic inhibition of noradrenaline release was not affected by hyperkalaemia, but was sensitive to metabolic inhibition and low degrees of acidosis.

Hypoxic enhancement of evoked noradrenaline release from the human neuroblastoma SH-SY5Y

The effects of chronic hypoxia (2.5% O(2), 24 h) on [3H]noradrenaline ([3H]NA) release evoked from human neuroblastoma SH-SY5Y cells by depolarisation and by activation of muscarinic receptors was investigated. Depolarization of cells with 100 mM K(+) evoked [3H]NA release, and chronic hypoxia enhanced this release significantly. In fluorimetric studies, the K(+)-evoked rises of [Ca(2+)](i) observed in response to 100 mM K(+) were also significantly enhanced. Muscarine-evoked [3H]NA release was also dramatically enhanced by chronic hypoxia. However, muscarine-induced release of Ca(2+) from intracellular stores and subsequent capacitative Ca(2+) entry was unaffected. The protein kinase C inhibitors GF 109 203X and RO-31-8220 did not prevent the enhancement of muscarine-evoked release caused by chronic hypoxia. These findings indicate that chronic hypoxia increases release of [3H]NA from human neuroblastoma SH-SY5Y cells. Enhancement of K(+)-evoked release was attributable to an enhancement of depolarisation-mediated Ca(2+) influx. In contrast, the larger enhancement of muscarine-evoked [3H]NA release was not due to greater release of Ca(2+) from internal stores, nor due to enhanced Ca(2+) influx. Furthermore, it was not attributable to activation of protein kinase C. These findings suggest that enhancement of sympathetic output, known to occur following prolonged hypoxia, may be mediated in part by enhancement of exocytosis.

Protection of neuronal uptake-1 inhibitors in ischemic and anoxic hearts by norepinephrine-dependent and -independent mechanisms

Cardiac ischemia and anoxia induce massive norepinephrine (NE) release, which is mediated by a reverse operation of uptake-1 and can be suppressed by uptake-1 inhibitors. We studied effects of uptake-1 inhibitors on incidence of ventricular fibrillation (VF%) and myocardial contracture in perfused rat hearts under ischemic or anoxic conditions. NE release occurred in hearts during ischemia or anoxia and was largely inhibited by desipramine, imipramine, and cocaine. The generation of inositol 1,4,5-trisphosphate (InsP3) during reperfusion also was abolished by desipramine. During anoxia/reoxygenation, VF (93 and 71%, respectively) and myocardial contracture occurred and were significantly inhibited by desipramine and by NE depletion. Regional ischemia and reperfusion induced high VF% (86 and 100%, respectively), which was reduced or abolished by desipramine and imipramine at 0.03 and 0.3 microM. During the ischemic phase, cocaine was similarly antiarrhythmic, as was a combination of timolol and prazosin, but NE depletion was not. In NE-depleted hearts, cocaine or the combination of timolol and prazosin showed limited effect on VF%, whereas both desipramine and imipramine abolished VF. In anesthetized rats in vivo, ischemic VF% was reduced by desipramine (30 vs. 92%; p < 0.01). In conclusion, uptake-1 inhibitors protect hearts against ischemia/reperfusion- and anoxia/reoxygenation-induced arrhythmias, partly because of the inhibition of locally mediated NE release. Other actions of desipramine and imipramine may contribute to the overall efficacy.

Effects of intracellular Ca2+ chelating on noradrenaline release in normoxic and anoxic hearts

1. Ischaemia and anoxia induce excessive noradrenaline (NA) release in the heart by a mechanism independent of both nerve activity and extracellular Ca2+. The present study was designed to examine the potential role of intracellular Ca2+ mobilization in anoxic NA release in the heart by chelating intracellular free Ca2+. 2. In normoxic hearts, preloading with an intracellular free Ca2+ chelator (BAPTA) reduced neuronal NA release by 65%, confirming the effectiveness of the loading protocol. Release of NA independent of nerve activity occurred in hearts subjected to a 40 min period of anoxic, substrate-free and nominal Ca(2+)-free perfusion. Loading hearts with BAPTA prior to anoxia failed to reduce NA overflow (1561 +/- 147 vs 1496 +/- 206 pmol/g over 40 min). Infusion with BAPTA (20 mumol/L) during the first 25 min of the anoxic period reduced the quantity of anoxic NA release by approximately 25% from 2013 +/- 124 to 1476 +/- 207 pmol/g (P < 0.05). 3. Our results confirm that anoxic NA release is predominantly a Ca(2+)-independent process with Ca2+ mobilization from endogenous storage playing only a minor contributing role.

Role of Ca2+ in metabolic inhibition-induced norepinephrine release in rat brain synaptosomes

Ischemia and simulated ischemic conditions induce enhanced release of norepinephrine (NE) in the brain and the heart. Although studies with neuronal preparations demonstrated a rise in [Ca2+]i under energy-depleted conditions, such release of NE in the heart appears to be predominantly Ca2+ independent. Since Ca2+ overload occurs in ischemia or energy depletion and since a rise in [Ca2+]i triggers exocytosis without membrane depolarization, we tested the possibility, using brain synaptosomes, that increased NE release could be, at least in part, a consequence of raised [Ca2+]i. Brain synaptosomes were incubated with Krebs-Henseleit medium, and ischemia was mimicked by treatment with metabolic inhibitors. NE content in incubation medium (supernatant) and synaptosomes was analyzed chromatographically. Treatment with metabolic inhibitors reduced ATP content by 75% and increased [Ca2+]i by more than fourfold within minutes. Metabolic inhibition elicited NE release, which started within 10 minutes and reached a maximum after 30 minutes, with a corresponding 55% reduction in synaptosomal NE content after 40 minutes. NE release, together with a marked increase in [Ca2+]i, was also induced in energy-depleted synaptosomes by Ca2+ repletion after incubation with the Ca(2+)-free medium. Effects on NE release of various interventions to prevent Ca2+ overload were tested. Omission of Ca2+ from the incubation medium or loading synaptosomes with the Ca2+ chelator BAPTA-AM (20 and 100 mumol/L) prevented NE release, indicating a Ca(2+)-dependent mechanism. Inhibition of Ca2+ channels with omega-conotoxin, cadmium, or nifedipine had no effect on NE release during energy depletion. In contrast, nickel and 3,4-dichlorobenzamil, Na(+)-Ca2+ exchange inhibitors, dose-dependently inhibited NE release. In conclusion, this study provides evidence that under energy-depleted conditions, Ca2+ overload in synaptosomes of noradrenergic neurons from the brain is an important mechanism for the enhanced release of NE and that a reversal of Na(+)-Ca2+ exchange may be the key pathway leading to intraneuronal Ca2+ overload.