Dopamine receptor subtypes in the human pulmonary arterial tree

Spiperone Stimulates Regeneration in Pulmonary Endothelium Damaged by Cigarette Smoke and Lipopolysaccharide

Background

Endothelial dysfunction and destruction of the pulmonary microcirculation are important pathogenic factors in chronic obstructive pulmonary disease (COPD). In COPD, bronchial obstruction is associated with endothelial dysfunction. Thus, new pharmacological treatment options aimed at restoring the pulmonary endothelium represent a clinical need in COPD therapy. Notch1 has been shown to protect cells against apoptosis, inflammation, and oxidative stress caused by cigarette smoke extract (CSE). Therefore, drug which effect on Notch1 may be a potential therapeutic target for COPD in the future.

Methods

In this study, we assessed the potential of spiperone to mediate regeneration of pulmonary endothelium in model of pulmonary emphysema induced by a CSE and lipopolysaccharide (LPS) in female C57BL/6 mice.

Results

Spiperone increased the number of capillaries as well as the expression of the CD31 in the alveolar tissue compared to the controls. Moreover, application of spiperone prevented alveolar wall destruction (DI), and reduced the area of emphysema. Lastly, we demonstrated that spiperone positively influenced mobilization and migration of endothelial progenitor cells (EPC, CD45⁻CD34⁺CD31⁺), CD309⁺-endothelial cells, and angiogenesis precursors (CD45⁻CD117⁺CD309⁺) into the lung. Spiperone administration significantly reduced the number Notch1 positive CD309⁺-endothelial cells and Notch1+ EPCs.

Conclusion

Overall, our results suggest that spiperone mediates endothelial regeneration in an animal model of COPD. Thus, it could represent a novel therapeutic approach for treatment of emphysema associated with COPD.

The Effects of Statins on Neurotransmission and Their Neuroprotective Role in Neurological and Psychiatric Disorders

Statins are among the most widely used drug classes in the world. Apart from their basic mechanism of action, which is lowering cholesterol levels, many pleiotropic effects have been described so far, such as anti-inflammatory and antiatherosclerotic effects. A growing number of scientific reports have proven that these drugs have a beneficial effect on the functioning of the nervous system. The first reports proving that lipid-lowering therapy can influence the development of neurological and psychiatric diseases appeared in the 1990s. Despite numerous studies about the mechanisms by which statins may affect the functioning of the central nervous system (CNS), there are still no clear data explaining this effect. Most studies have focused on the metabolic effects of this group of drugs, however authors have also described the pleiotropic effects of statins, pointing to their probable impact on the neurotransmitter system and neuroprotective effects. The aim of this paper was to review the literature describing the impacts of statins on dopamine, serotonin, acetylcholine, and glutamate neurotransmission, as well as their neuroprotective role. This paper focuses on the mechanisms by which statins affect neurotransmission, as well as on their impacts on neurological and psychiatric diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), vascular dementia (VD), stroke, and depression. The pleiotropic effects of statin usage could potentially open floodgates for research in these treatment domains, catching the attention of researchers and clinicians across the globe.

Perivascular Innervation of the Pulmonary Artery in Human and Swine: A Comparative Study for the Development of an Experimental Model of Denervation

For studying the possibility of using catheter denervation of the pulmonary artery for the treatment of pulmonary hypertension, large animals, such as pigs, are more suitable, because the diameter of the pulmonary artery in this case allows manipulation of the ablation catheter. The study of the perivascular adipose tissue of the trunk and bifurcation of the pulmonary artery in humans and pigs revealed differences in the density and diameter of nerve fibers, but their depth did not differ. Immunohistochemical analysis with different markers of the autonomic nervous system receptors revealed similar receptor profile in human and pigs, though the expression of all studied markers in pigs was less pronounced than in humans. These findings attest to similarity of the innervation of the pulmonary arteries in humans and pigs under normal conditions.

Low-Frequency (20 kHz) Ultrasonic Modulation of Drug Action

We tested the effect of low-frequency ultrasound (LUS, 20 kHz, 4 W/cm²) on the function of rat mesentery and human pulmonary arteries with wire myography. The vessels were induced to contract with either noradrenaline or physiologic saline solution (PSS) with a high potassium concentration (KPSS) and then incubated with capsaicin (2.1 × 10^-7 M, TRPV1 [transient receptor potential vanilloid 1] activator), dopamine (1 × 10^-4 M, dopamine and α₂-receptor activator), or fenoldopam (dopamine_A1 receptor agonist, 1 × 10^-4 M) with and without glibenclamide (1 μM, KATP [adenosine triphosphate {sensitive potassium channel (ATP)}-sensitive potassium channel] inhibitor and α₂-receptor modulator), and insonated. Vessels were incubated in Ca²⁺-free PSS and induced to contract with added extracellular Ca²⁺ and noradrenaline. Pulmonary arteries were induced to contract with KPSS and dopamine. Then the vessels were insonated. LUS inhibited the influx of external Ca²⁺, inhibited the dopamine-induced vasoconstriction in the KPSS (glibenclamide reversible), reduced the capsaicin-induced vasorelaxation, increased the gentamicin-induced vasorelaxation and increased the dopamine-induced contraction in the KPSS in human pulmonary arteries.

Blockade of Dopamine D2 Receptors as a Novel Approach to Stimulation of Notch1+ Endothelial Progenitor Cells and Angiogenesis in C57BL/6 Mice with Pulmonary Emphysema Induced by Proteases and Deficiency of α1-Antitrypsin

We studied the effects of spiperone, a selective blocker of dopamine D2 receptors, on the model of pulmonary emphysema provoked by administration of elastase and D-galactosamine hydrochloride to female C57BL/6 mice and characterized by activation of proteases in the lungs and systemic deficiency of its inhibitor α1-antitrypsin. In this model, spiperone prevented the development of inflammatory reaction and reduced the area of emphysematous expanded alveolar tissue. The expression of angiogenic marker CD31 in the lungs increased under these conditions. Regeneration of the damaged microvascular bed under the action of spiperone resulted from recruiting of Notch1⁺ endothelial progenitor cells (CD45^-CD31⁺CD34⁺) into the lungs and blockade of the inhibitory effect of dopamine on phosphorylation of VEGF-2 receptors in endothelial cells of different maturity. In addition, spiperone produced a protective effect on hepatocytes and restored the production and secretion of α1-antitrypsin by these cells.

Intra-pulmonary arteriovenous anastomoses and pulmonary gas exchange: evaluation by microspheres, contrast echocardiography and inert gas elimination

KEY POINTS

Imaging techniques such as contrast echocardiography suggest that anatomical intra-pulmonary arteriovenous anastomoses (IPAVAs) are present at rest and are recruited to a greater extent in conditions such as exercise. IPAVAs have the potential to act as a shunt, although gas exchange methods have not demonstrated significant shunt in the normal lung. To evaluate this discrepancy, we compared anatomical shunt with 25-µm microspheres to contrast echocardiography, and gas exchange shunt measured by the multiple inert gas elimination technique (MIGET). Intra-pulmonary shunt measured by 25-µm microspheres was not significantly different from gas exchange shunt determined by MIGET, suggesting that MIGET does not underestimate the gas exchange consequences of anatomical shunt. A positive agitated saline contrast echocardiography score was associated with anatomical shunt measured by microspheres. Agitated saline contrast echocardiography had high sensitivity but low specificity to detect a ≥1% anatomical shunt, frequently detecting small shunts inconsequential for gas exchange.

ABSTRACT

The echocardiographic visualization of transpulmonary agitated saline microbubbles suggests that anatomical intra-pulmonary arteriovenous anastomoses are recruited during exercise, in hypoxia, and when cardiac output is increased pharmacologically. However, the multiple inert gas elimination technique (MIGET) shows insignificant right-to-left gas exchange shunt in normal humans and canines. To evaluate this discrepancy, we measured anatomical shunt with 25-µm microspheres and compared the results to contrast echocardiography and MIGET-determined gas exchange shunt in nine anaesthetized, ventilated canines. Data were acquired under the following conditions: (1) at baseline, (2) 2 µg kg-1  min-1 i.v. dopamine, (3) 10 µg kg-1  min-1 i.v. dobutamine, and (4) following creation of an intra-atrial shunt (in four animals). Right to left anatomical shunt was quantified by the number of 25-µm microspheres recovered in systemic arterial blood. Ventilation-perfusion mismatch and gas exchange shunt were quantified by MIGET and cardiac output by direct Fick. Left ventricular contrast scores were assessed by agitated saline bubble counts, and separately by appearance of 25-µm microspheres. Across all conditions, anatomical shunt measured by 25-µm microspheres was not different from gas exchange shunt measured by MIGET (microspheres: 2.3 ± 7.4%; MIGET: 2.6 ± 6.1%, P = 0.64). Saline contrast bubble score was associated with microsphere shunt (ρ = 0.60, P < 0.001). Agitated saline contrast score had high sensitivity (100%) to detect a ≥1% shunt, but low specificity (22-48%). Gas exchange shunt by MIGET does not underestimate anatomical shunt measured using 25-µm microspheres. Contrast echocardiography is extremely sensitive, but not specific, often detecting small anatomical shunts which are inconsequential for gas exchange.

Miniaturized neural system for chronic, local intracerebral drug delivery

Recent advances in medications for neurodegenerative disorders are expanding opportunities for improving the debilitating symptoms suffered by patients. Existing pharmacologic treatments, however, often rely on systemic drug administration, which result in broad drug distribution and consequent increased risk for toxicity. Given that many key neural circuitries have sub-cubic millimeter volumes and cell-specific characteristics, small-volume drug administration into affected brain areas with minimal diffusion and leakage is essential. We report the development of an implantable, remotely controllable, miniaturized neural drug delivery system permitting dynamic adjustment of therapy with pinpoint spatial accuracy. We demonstrate that this device can chemically modulate local neuronal activity in small (rodent) and large (nonhuman primate) animal models, while simultaneously allowing the recording of neural activity to enable feedback control.

Dopamine outside the brain: The eye, cardiovascular system and endocrine pancreas

Dopamine (DA) and DA receptors (DR) have been extensively studied in the central nervous system (CNS), but their role in the periphery is still poorly understood. Here we summarize data on DA and DRs in the eye, cardiovascular system and endocrine pancreas, three districts where DA and DA-related drugs have been studied and the expression of DR documented. In the eye, DA modulates ciliary blood flow and aqueous production, which impacts on intraocular pressure and glaucoma. In the cardiovascular system, DA increases blood pressure and heart activity, mostly through a stimulation of adrenoceptors, and induces vasodilatation in the renal circulation, possibly through D1R stimulation. In pancreatic islets, beta cells store DA and co-release it with insulin. D1R is mainly expressed in beta cells, where it stimulates insulin release, while D2R is expressed in both beta and delta cells (in the latter at higher level), where it inhibits, respectively, insulin and somatostatin release. The formation of D2R-somatostatin receptor 5 heteromers (documented in the CNS), might add complexity to the system. DA may exert both direct autocrine effects on beta cells, and indirect paracrine effects through delta cells and somatostatin. Bromocriptine, an FDA approved drug for diabetes, endowed with both D1R (antagonistic) and D2R (agonistic) actions, may exert complex effects, resulting from the integration of direct effects on beta cells and paracrine effects from delta cells. A full comprehension of peripheral DA signaling deserves further studies that may generate innovative therapeutic drugs to manage conditions such as glaucoma, cardiovascular diseases and diabetes.

Dopaminergic receptor-ligand binding assays based on molecularly imprinted polymers on quartz crystal microbalance sensors

Molecularly imprinted polymers (MIPs) have been successfully applied as selective materials for assessing the binding activity of agonist and antagonist of dopamine D1 receptor (D1R) by using quartz crystal microbalance (QCM). In this study, D1R derived from rat hypothalamus was used as a template and thus self-organized on stamps. Those were pressed into an oligomer film consisting of acrylic acid: N-vinylpyrrolidone: N,N'-(1,2-dihydroxyethylene) bis-acrylamide in a ratio of 2:3:12 spin coated onto a dual electrode QCM. Such we obtained one D1R-MIP-QCM electrode, whereas the other electrode carried the non-imprinted control polymer (NIP) that had remained untreated. Successful imprinting of D1R was confirmed by AFM. The polymer can re-incorporate D1R leading to frequency responses of 100-1200Hz in a concentration range of 5.9-47.2µM. In a further step such frequency changes proved inherently useful for examining the binding properties of test ligands to D1R. The resulting mass-sensitive measurements revealed Kd of dopamine∙HCl, haloperidol, and (+)-SCH23390 at 0.874, 25.6, and 0.004nM, respectively. These results correlate well with the values determined in radio ligand binding assays. Our experiments revealed that D1R-MIP sensors are useful for estimating the strength of ligand binding to the active single site. Therefore, we have developed a biomimetic surface imprinting strategy for QCM studies of D1R-ligand binding and presented a new method to ligand binding assay for D1R.

Cocaine enhances HIV-1 gp120-induced lymphatic endothelial dysfunction in the lung

Pulmonary complications are common in both AIDS patients and cocaine users. We addressed the cellular and molecular mechanisms by which HIV and cocaine may partner to induce their deleterious effects. Using primary lung lymphatic endothelial cells (L-LECs), we examined how cocaine and HIV-1 gp120, alone and together, modulate signaling and functional properties of L-LECs. We found that brief cocaine exposure activated paxillin and induced cytoskeletal rearrangement, while sustained exposure increased fibronectin (FN) expression, decreased Robo4 expression, and enhanced the permeability of L-LEC monolayers. Moreover, incubating L-LECs with both cocaine and HIV-1 gp120 exacerbated hyperpermeability, significantly enhanced apoptosis, and further impaired in vitro wound healing as compared with cocaine alone. Our studies also suggested that the sigma-1 receptor (Sigma-1R) and the dopamine-4 receptor (D4R) are involved in cocaine-induced pathology in L-LECs. Seeking clinical correlation, we found that FN levels in sera and lung tissue of HIV(+) donors were significantly elevated as compared to HIV(-) donors. Our in vitro data demonstrate that cocaine and HIV-1 gp120 induce dysfunction and damage of lung lymphatics, and suggest that cocaine use may exacerbate pulmonary edema and fibrosis associated with HIV infection. Continued exploration of the interplay between cocaine and HIV should assist the design of therapeutics to ameliorate HIV-induced pulmonary disorders within the drug using population.

Ion channels and transporters as therapeutic targets in the pulmonary circulation

Pulmonary circulation is a low pressure, low resistance, high flow system. The low resting vascular tone is maintained by the concerted action of ion channels, exchangers and pumps. Under physiological as well as pathophysiological conditions, they are targets of locally secreted or circulating vasodilators and/or vasoconstrictors, leading to changes in expression or to posttranslational modifications. Both structural changes in the pulmonary arteries and a sustained increase in pulmonary vascular tone result in pulmonary vascular remodeling contributing to morbidity and mortality in pediatric and adult patients. There is increasing evidence demonstrating the pivotal role of ion channels such as K(+) and Cl(-) or transient receptor potential channels in different cell types which are thought to play a key role in vasoconstrictive remodeling. This review focuses on ion channels, exchangers and pumps in the pulmonary circulation and summarizes their putative pathophysiological as well as therapeutic role in pulmonary vascular remodeling. A better understanding of the mechanisms of their actions may allow for the development of new options for attenuating acute and chronic pulmonary vasoconstriction and remodeling treating the devastating disease pulmonary hypertension.

Dopamine D₄ receptors inhibit proliferation and migration of vascular smooth muscle cells induced by insulin via down-regulation of insulin receptor expression

Vascular smooth muscle cells (VSMCs) proliferation and migration, which are central in the development of vascular diseases, are regulated by numerous hormones and humoral factors. Activation of the insulin receptor stimulates VSMCs proliferation while dopamine receptors, via D₁ and D₃ receptors, inhibit the stimulatory effects of norepinephrine on VSMCs proliferation. We hypothesize that activation of the D₄ dopamine receptor may also inhibit the proliferation and migration of VSMCs, therefore, inhibit atherosclerosis. Our current study found that insulin increased the proliferation and migration of A10 cells, an effect that was reduced in the presence of a D₄ receptor agonist, PD168077. The negative effect of the D₄ receptor on insulin’s action may be via decreasing insulin receptor expression, because activation of the D₄ receptor inhibited insulin receptor protein and mRNA expressions, indicating that the regulation occured at the transcriptional or post-transcriptional levels. To determine whether or not the inhibition of D₄ receptor on insulin-mediated proliferation and migration of VSMCs has physiological significance, hyper-insulinemic Sprague–Dawley rats with balloon-injured carotid artery were treated with a D₄ agonist, PD168077, (6 mg/kg/d) for 14 days. We found that PD168077 significantly inhibited neointimal formation by inhibition of VSMC proliferation. This study suggests that activation of the D₄ receptor suppresses the proliferation and migration of VSMCs, therefore, inhibit atherosclerosis. The D₄ receptor may be a potential therapeutic target to reduce the effects of insulin on artery remodeling.

The dopamine D1 receptor is expressed and facilitates relaxation in airway smooth muscle

Background

Dopamine signaling is mediated by G_s protein-coupled “D₁-like” receptors (D₁ and D₅) and G_i-coupled “D₂-like” receptors (D_2-4). In asthmatic patients, inhaled dopamine induces bronchodilation. Although the G_i-coupled dopamine D₂ receptor is expressed and sensitizes adenylyl cyclase activity in airway smooth muscle (ASM) cells, the G_s-coupled dopamine D₁-like receptor subtypes have never been identified on these cells. Activation of G_s-coupled receptors stimulates cyclic AMP (cAMP) production through the stimulation of adenylyl cyclase, which promotes ASM relaxation. We questioned whether the dopamine D₁-like receptor is expressed on ASM, and modulates its function through G_s-coupling.

Methods

The mRNA and protein expression of dopamine D₁-like receptor subtypes in both native human and guinea pig ASM tissue and cultured human ASM (HASM) cells was measured. To characterize the stimulation of cAMP through the dopamine D₁ receptor, HASM cells were treated with dopamine or the dopamine D₁-like receptor agonists (A68930 or SKF38393) before cAMP measurements. To evaluate whether the activation of dopamine D₁ receptor induces ASM relaxation, guinea pig tracheal rings suspended under isometric tension in organ baths were treated with cumulatively increasing concentrations of dopamine or A68930, following an acetylcholine-induced contraction with or without the cAMP-dependent protein kinase (PKA) inhibitor Rp-cAMPS, the large-conductance calcium-activated potassium (BK_Ca) channel blocker iberiotoxin, or the exchange proteins directly activated by cAMP (Epac) antagonist NSC45576.

Results

Messenger RNA encoding the dopamine D₁ and D₅ receptors were detected in native human ASM tissue and cultured HASM cells. Immunoblots confirmed the protein expression of the dopamine D₁ receptor in both native human and guinea pig ASM tissue and cultured HASM cells. The dopamine D₁ receptor was also immunohistochemically localized to both human and guinea pig ASM. The dopamine D₁-like receptor agonists stimulated cAMP production in HASM cells, which was reversed by the selective dopamine D₁-like receptor antagonists SCH23390 or SCH39166. A68930 relaxed acetylcholine-contracted guinea pig tracheal rings, which was attenuated by Rp-cAMPS but not by iberiotoxin or NSC45576.

Conclusions

These results demonstrate that the dopamine D₁ receptors are expressed on ASM and regulate smooth muscle force via cAMP activation of PKA, and offer a novel target for therapeutic relaxation of ASM.

The effects of dobutamine and dopamine on intrapulmonary shunt and gas exchange in healthy humans

The development of intrapulmonary shunts with increased cardiac output during exercise in healthy humans has been reported in several recent studies, but mechanisms governing their recruitment remain unclear. Dobutamine and dopamine are inotropes commonly used to augment cardiac output; however, both can increase venous admixture/shunt fraction (Qs/Qt). It is possible that, as with exercise, intrapulmonary shunts are recruited with increased cardiac output during dobutamine and/or dopamine infusion that may contribute to the observed increase in Qs/Qt. The purpose of this study was to examine how dobutamine and dopamine affect intrapulmonary shunt and gas exchange. Nine resting healthy subjects received serial infusions of dobutamine and dopamine at incremental doses under normoxic and hyperoxic (inspired O(2) fraction = 1.0) conditions. At each step, alveolar-to-arterial Po(2) difference (A-aDo(2)) and Qs/Qt were calculated from arterial blood gas samples, intrapulmonary shunt was evaluated using contrast echocardiography, and cardiac output was calculated by Doppler echocardiography. Both dobutamine and dopamine increased cardiac output and Qs/Qt. Intrapulmonary shunt developed in most subjects with both drugs and paralleled the increase in Qs/Qt. A-aDo(2) was unchanged due to a concurrent rise in mixed venous oxygen content. Hyperoxia consistently eliminated intrapulmonary shunt. These findings contribute to our present understanding of the mechanisms governing recruitment of these intrapulmonary shunts as well as their impact on gas exchange. In addition, given the deleterious effect on Qs/Qt and the risk of neurological complications with intrapulmonary shunts, these findings could have important implications for use of dobutamine and dopamine in the clinical setting.

The dopamine D(2) receptor is expressed and sensitizes adenylyl cyclase activity in airway smooth muscle

Dopamine receptors are G protein-coupled receptors that are divided into two subgroups, "D(1)-like" receptors (D(1) and D(5)) that couple to the G(s) protein and "D(2)-like" receptors (D(2), D(3), and D(4)) that couple to G(i). Although inhaled dopamine has been reported to induce bronchodilation in patients with asthma, functional expression of dopamine receptor subtypes has never been described on airway smooth muscle (ASM) cells. Acute activation of G(i)-coupled receptors inhibits adenylyl cyclase activity and cAMP synthesis, which classically impairs ASM relaxation. In contrast, chronic activation of G(i)-coupled receptors produces a paradoxical enhancement of adenylyl cyclase activity referred to as heterologous sensitization. We questioned whether the dopamine D(2)-like receptor is expressed on ASM, whether it exhibits classical G(i)-coupling, and whether it modulates ASM function. We detected the mRNA encoding the dopamine D(2) receptor in total RNA isolated from native human ASM and from cultured human airway smooth muscle (HASM) cells. Immunoblots identified the dopamine D(2) receptor protein in both native human and guinea pig ASM and cultured HASM cells. The dopamine D(2) receptor protein was immunohistochemically localized to both human and guinea pig ASM. Acute activation of the dopamine D(2) receptor by quinpirole inhibited forskolin-stimulated adenylyl cyclase activity in HASM cells, which was blocked by the dopamine D(2) receptor antagonist L-741626. In contrast, the chronic pretreatment (1 h) with quinpirole potentiated forskolin-stimulated adenylyl cyclase activity, which was inhibited by L-741626, the phospholipase C inhibitor U73122, or the protein kinase C inhibitor GF109203X. Quinpirole also stimulated inositol phosphate synthesis, which was inhibited by L-741626 or U73122. Chronic pretreatment (1 h) of the guinea pig tracheal rings with quinpirole significantly potentiated forskolin-induced airway relaxation, which was inhibited by L-741626. These results demonstrate that functional dopamine D(2) receptors are expressed on ASM and could be a novel therapeutic target for the relaxation of ASM.

Lack of renal dopamine D5 receptors promotes hypertension

Disruption of the dopamine D(5) receptor gene in mice increases BP and causes salt sensitivity. To determine the role of renal versus extrarenal D(5) receptors in BP regulation, we performed cross-renal transplantation experiments. BP was similar between wild-type mice and wild-type mice transplanted with wild-type kidneys, indicating that the transplantation procedure did not affect BP. BP was lower among D(5)(-/-) mice transplanted with wild-type kidneys than D(5)(-/-) kidneys, demonstrating that the renal D(5) receptors are important in BP control. BP was higher in wild-type mice transplanted with D(5)(-/-) kidneys than wild-type kidneys but not significantly different from syngenic transplanted D(5)(-/-) mice, indicating the importance of the kidney in the development of hypertension. On a high-salt diet, all mice with D(5)(-/-) kidneys excreted less sodium than mice with wild-type kidneys. Transplantation of a wild-type kidney into a D(5)(-/-) mouse decreased the renal expression of AT(1) receptors and Nox-2. Conversely, transplantation of a D(5)(-/-) kidney into a wild-type mouse increased the expression of both, suggesting that both renal and extrarenal factors are important in the regulation of AT(1) receptor and Nox-2 expression. These results highlight the role of renal D(5) receptors in BP homeostasis and the pathogenesis of hypertension.

Dopamine D2 receptor mRNA expression is increased in the jugular-nodose ganglia of rats with nitrogen dioxide-induced chronic bronchitis

The bronchodilatatory effect of inhaled dopamine or dopamine D(2) receptor agonists in cases of bronchial constriction may involve the suppression of pathologically increased airway sensory nerve activity. The aim of this study is to investigate the regulation of the dopamine D(2) receptor mRNA expression in the ganglia of rats with nitrogen dioxide-induced chronic bronchitis compared with that in ganglia of healthy control animals. Rats were exposed to nitrogen dioxide (10 ppm, 20 d) and dopamine D(2) receptor mRNA levels in sensory ganglia (jugular-nodose, trigeminal, cervical dorsal root and thoracic dorsal root ganglia) were examined by quantitative real-time polymerase chain reaction and compared to control tissues. Whereas for trigeminal and dorsal root ganglia the dopamine D(2) receptor expression levels showed no difference between both animal groups, there was a significant (p<0.05) increase in the jugular-nodose ganglia with a 2.1-fold factor. The increase of dopamine D(2) receptor mRNA in jugular-nodose sensory neurons which innervate the airways may represent a neurochemical basis for the effects seen in man and animal models following topical administration of dopamine or dopamine agonists onto the respiratory epithelium.

Reactive oxygen species and dopamine receptor function in essential hypertension

Essential hypertension is a major risk factor for stroke, myocardial infarction, and heart and kidney failure. Dopamine plays an important role in the pathogenesis of hypertension by regulating epithelial sodium transport and by interacting with vasoactive hormones and humoral factors. However, the mechanisms leading to impaired dopamine receptor function in hypertension states are not clear. Compelling experimental evidence indicates a role of reactive oxygen species (ROS) in hypertension, and there are increasing pieces of evidence showing that in conditions associated with oxidative stress, which is present in hypertensive states, dopamine receptor effects, such as natriuresis, diuresis, and vasodilation, are impaired. The goal of this review is to present experimental evidence that has led to the conclusion that decreased dopamine receptor function increases ROS activity and vice versa. Decreased dopamine receptor function and increased ROS production, working in concert or independent of each other, contribute to the pathogenesis of essential hypertension.

Dysregulation of dopamine-dependent mechanisms as a determinant of hypertension: studies in dopamine receptor knockout mice

Dopamine plays an important role in the pathogenesis of hypertension by regulating epithelial sodium transport and by interacting with vasoactive hormones/humoral factors, such as aldosterone, angiotensin, catecholamines, endothelin, oxytocin, prolactin pro-opiomelancortin, reactive oxygen species, renin, and vasopressin. Dopamine receptors are classified into D(1)-like (D(1) and D(5)) and D(2)-like (D(2), D(3), and D(4)) subtypes based on their structure and pharmacology. In recent years, mice deficient in one or more of the five dopamine receptor subtypes have been generated, leading to a better understanding of the physiological role of each of the dopamine receptor subtypes. This review summarizes the results from studies of various dopamine receptor mutant mice on the role of individual dopamine receptor subtypes and their interactions with other G protein-coupled receptors in the regulation of blood pressure.