Dopamine D2 receptor stimulation inhibits angiotensin II-induced hypertrophy in cultured neonatal rat ventricular myocytes

Anti-Inflammatory Effects of Peripheral Dopamine

Dopamine is synthesized in the nervous system where it acts as a neurotransmitter. Dopamine is also synthesized in a number of peripheral organs as well as in several types of cells and has organ-specific functions and, as demonstrated more recently, is involved in the regulation of the immune response and inflammatory reaction. In particular, the renal dopaminergic system is very important in the regulation of sodium transport and blood pressure and is particularly sensitive to stimuli that cause oxidative stress and inflammation. This review is focused on how dopamine is synthesized in organs and tissues and the mechanisms by which dopamine and its receptors exert their effects on the inflammatory response.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

The effect and mechanism of dopamine D1 receptors on the proliferation of osteosarcoma cells

The physiological and pathological roles of dopamine D1 receptors (DR1) in the regulation of functions in tissues and organs have been recognized. However, whether DR1 are expressed in the osteosarcoma cells and inhibit the proliferation of these cells is unknown. In the present study, we found that DR1 were expressed in the osteosarcoma cells (OS732 cells). SKF-38393 (DR1 agonist) and the overexpression of DR1 decreased the proliferation of OS732 cells; SCH-23390 (DR1 antagonist) and the knockdown of DR1 increased the proliferation of OS732 cells, and both SCH-23390 and the knockdown of DR1 abolished the effect of SKF-38393 on the proliferation of OS732 cells. In addition, SKF-38393 down-regulated the phosphorylation of ERK1/2, PI3K, and Akt; SCH-23390 up-regulated the phosphorylation of ERK1/2, PI3K, and Akt, and SCH-23390 cancelled the effect of SKF-38393. The effect of SKF-38393 on the phosphorylation of ERK1/2, PI3K, and Akt and the proliferation of OS732 cells was similar to PD98059 (an ERK inhibitor) or LY294002 (a PI3K inhibitor), respectively. In conclusion, our results suggest that DR1 are expressed in the osteosarcoma cells and inhibit the proliferation of osteosarcoma cells by the down-regulation of the ERK1/2 and PI3K-Akt pathways. These findings provide a novel target for the treatment of the osteosarcoma.

Pharmacological analysis of dopamine modulation in the Drosophila melanogaster larval heart

Dopamine (DA) and other neurotransmitters affect nonneuronal tissues in insects by circulating in the hemolymph. In several organisms, DA has been shown to modulate distinct aspects of cardiac function but the signal transduction pathways that mediate dopaminergic effects on the heart are not well characterized. Here, we used a semiintact Drosophila melanogaster larva preparation and drugs targeting DA receptors and canonical second messenger pathways to identify signaling cascades that mediate the effect of DA on a myogenic heart. DA has a positive chronotropic effect that is mimicked by SKF38393 (type-1 DA receptor agonist) and quinpirole (type-2 DA receptor agonist). SCH23390 and spiperone (type-1 and type-2 DA receptor antagonists) are moderately effective at inhibiting DA's effect. An adenylate cyclase inhibitor (SQ,22536) is also effective at blocking the stimulatory effect of DA but the drug has its own dose-dependent effect. Activation of protein kinase C with a diacylglycerol analog has a stimulatory effect on heart rate (HR). These results suggest that (1) both DA receptor subtypes are expressed in third instar larva cardiac myocytes to increase HR in response to rising levels of DA in the hemolymph, and (2) canonical second messenger pathways modulate HR in D. melanogaster larvae. Having these disparate signaling cascades converge toward a common modulatory function appears redundant, but in the context of multiple cardioactive chemicals this redundancy is likely to increase the fidelity of signal transduction.

D2 dopamine receptor antagonist raclopride induces non-canonical autophagy in cardiac myocytes

Cell death by autophagy is an important means of maintaining cellular homeostasis in adult cardiac myocytes. Autophagy was previously shown to exert a cardioprotective effect, suggesting that modulation of autophagy pathways is a potential therapeutic strategy in the treatment of heart disease. Although dopamine is known to induce autophagy in neuroblastoma cells, the underlying mechanism and the types of dopamine receptors involved in this process remain unclear. In this study, we used various dopamine receptor antagonists and agonists to identify the specific dopamine receptor that mediates induction of autophagy. We evaluated autophagy induction by the expression of autophagy markers in neonatal rat ventricular cardiac myocytes. We evaluated intracellular calcium levels using Fluo-3/AM and demonstrated autophagy-induced morphological changes in cardiac myocytes using electron microscopy. We also examined the pathway for dopamine-induced autophagy using RNAi-mediated gene knockdown. Raclopride, the well-documented D2 receptor antagonist, significantly upregulated autophagy in cardiac myocytes via an mTOR-independent pathway. There was no difference in intracellular calcium levels between raclopride-treated cells and untreated cells. siRNA-mediated knockdown of Rab9 resulted in decreased expression of autophagy markers in raclopride-treated cells. Interestingly, siRNA-mediated knockdown of Atg7 resulted in a significant increase in Rab9 levels in raclopride-treated cells, suggesting that blocking the classical autophagy pathway results in activation of an alternative pathway. Our study suggests that (1) the D2 dopamine receptor plays a role in autophagy and (2) raclopride mediated a non-canonical autophagy pathway in cardiac myocytes via Rab9.

Role of dopamine D2 receptors in ischemia/reperfusion induced apoptosis of cultured neonatal rat cardiomyocytes

Background

Myocardial ischemia/reperfusion injury is the major cause of morbidity and mortality for cardiovascular diseases. Dopamine D₂ receptors are expressed in cardiac tissues. However, the roles of dopamine D₂ receptors in myocardial ischemia/reperfusion injury and cardiomyocyte apoptosis are unclear. Here we investigated the effects of both dopamine D₂ receptors agonist (bromocriptine) and antagonist (haloperidol) on apoptosis of cultured neonatal rat ventricular myocytes induced by ischemia/reperfusion injury.

Methods

Myocardial ischemia/reperfusion injury was simulated by incubating primarily cultured neonatal rat cardiomyocytes in ischemic (hypoxic) buffer solution for 2 h. Thereafter, these cells were incubated for 24 h in normal culture medium.

Results

Treatment of the cardiomyocytes with 10 μM bromocriptine significantly decreased lactate dehydrogenase activity, increased superoxide dismutase activity, and decreased malondialdehyde content in the culture medium. Bromocriptine significantly inhibited the release of cytochrome c, accumulation of [Ca²⁺]_i, and apoptosis induced by ischemia/reperfusion injury. Bromocriptine also down-regulated the expression of caspase-3 and -9, Fas and Fas ligand, and up-regulated Bcl-2 expression. In contrast, haloperidol (10 μM) had no significant effects on the apoptosis of cultured cardiomyocytes under the aforementioned conditions.

Conclusions

These data suggest that activation of dopamine D₂ receptors can inhibit apoptosis of cardiomyocytes encountered during ischemia/reperfusion damage through various pathways.

Increased expression of calcium-sensing receptors induced by ox-LDL amplifies apoptosis of cardiomyocytes during simulated ischaemia-reperfusion

1. Acute myocardial infarction (AMI) is strongly associated with atherosclerosis, and is responsible for significant morbidity and mortality worldwide. The pathogenic mechanisms that underlie atherosclerosis and AMI are undefined at present. The calcium-sensing receptor (CaSR) is a member of the superfamily of G-protein coupled receptors. It has been demonstrated previously that the expression of CaSR is increased in atherosclerotic cardiac tissue of rats. It has also been suggested that CaSR has a crucial role in cardiac ischaemia-reperfusion injury, apoptosis and hypertrophy. However, it remains to be determined whether an increase in the expression of CaSR influences the sensitivity of cardiomyocytes to AMI. 2. The present study used cultured ventricular cardiomyocytes from neonatal rats to investigate the effect of oxidized low-density lipoprotein (ox-LDL), ischaemia-reperfusion, GdCl(3) (an agonist of CaSR) and NPS-2390 (an antagonist of CaSR) on the expression of CaSR. The amount of apoptosis, alterations in the morphology of the cells, the intracellular calcium concentration ([Ca(2+)](i)) and components of critical mitochondrial pathways were also analysed. 3. Cardiomyocytes treated with ox-LDL showed upregulated expression of CaSR, cytochrome c (cyt-c), Bax and activated caspase 3 (17 kD) and downregulated expression of Bcl-2, as well as elevated [Ca(2+)](i) and apoptosis. Application of GdCl(3) augmented these effects, and NPS-2390 decreased the expression of CaSR and reduced apoptosis. 4. In conclusion, ox-LDL was found to increase the expression of CaSR in a manner that was dependent on time and dose. It also augmented apoptosis during simulated ischaemia-reperfusion in cultured ventricular cardiomyocytes from neonatal rats.

Effects of dietary fat and enterostatin on dopamine and 5-hydroxytrytamine release from rat striatal slices

Studies have demonstrated defects of DA and 5HT neurotransmission in dietary fat induced obese animals. In the present study, we used a perfusion system to assay the release of DA and 5HT from striatal slices preloaded with [(3)H]-DA or [(3)H]-5HT. The release of both DA and 5HT from striatal slices of rats fed a high fat diet for 10 days, but not 3 days, was reduced when compared to striatal slices taken from rats fed a low fat diet. Enterostatin, an endogenous pentapeptide inhibits dietary fat intake when administered peripherally and centrally in animals. The central mechanism for the action of enterostatin is not yet determined even though several mechanisms have been suggested. We have shown that enterostatin enhanced [(3)H]-DA release, but not [(3)H]-5HT release from striatal slices of rats that had been adapted to high fat diet for 10 days. The enterostatin-induced increase in [(3)H]-DA release was blocked by nomifensine. Enterostatin did not alter [(3)H]-DA or [(3)H]-5HT release from striatal slices of rats adapted to high fat or low fat diet feeding for 3 days. These findings suggest that enterostatin may inhibit dietary fat intake by blocking dopamine reuptake transport to increase central striatal DA release from rats that have acquired diminished dopamine signal after an adaptive period of fat consumption.