Angiotensin-II type 1 receptor-mediated hypertension in D4 dopamine receptor-deficient mice

The salt sensitivity of Drd4-null mice is associated with the upregulations of sodium transporters in kidneys

To explore the mechanism of the hypertension in dopamine receptor-4 (Drd4) null mice, we determined the salt sensitivity and renal sodium transport proteins in Drd4-/- and Drd4+/+ mice with varied salt diets. On normal NaCl diet (NS), mean arterial pressures (MAP, telemetry) were higher in Drd4-/- than Drd4+/+; Low NaCl diet (LS) tended to decrease MAP in both strains; high NaCl diet (HS) elevated MAP with sodium excretion decreased and pressure-natriuresis curve shifted to right in Drd4-/- relative to Drd4+/+ mice. Drd4-/- mice exhibited increased renal sodium-hydrogen exchanger 3 (NHE3), sodium-potassium-2-chloride cotransporter (NKCC2), sodium-chloride cotransporter (NCC), and outer medullary α-epithelial sodium channel (αENaC) on NS, decreased NKCC2, NCC, αENaC, and αNa+-K+-ATPase on LS, and increased αENaC on HS. NKCC2, NCC, αENaC, and αNa+-K+-ATPase in plasma membrane were greater in Drd4-/- than in Drd4+/+ mice with HS. D4R was expressed in proximal and distal convoluted tubules, thick ascending limbs, and outer medullary collecting ducts and colocalized with NKCC2 and NCC. The phosphorylation of NKCC2 was enhanced but ubiquitination was reduced in the KO mice. There were no differences between the mouse strains in serum aldosterone concentrations and urinary dopamine excretions despite their changes with diets. The mRNA expressions of renal NHE3, NKCC2, NCC, and αENaC on NS were not altered in Drd4-/- mice. Thus, increased protein expressions of NHE3, NKCC2, NCC and αENaC are associated with hypertension in Drd4-/- mice; increased plasma membrane protein expression of NKCC2, NCC, αENaC, and αNa+-K+-ATPase may mediate the salt sensitivity of Drd4-/- mice.

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.

Role of Dopamine in the Heart in Health and Disease

Dopamine has effects on the mammalian heart. These effects can include an increase in the force of contraction, and an elevation of the beating rate and the constriction of coronary arteries. Depending on the species studied, positive inotropic effects were strong, very modest, or absent, or even negative inotropic effects occurred. We can discern five dopamine receptors. In addition, the signal transduction by dopamine receptors and the regulation of the expression of cardiac dopamine receptors will be of interest to us, because this might be a tempting area of drug development. Dopamine acts in a species-dependent fashion on these cardiac dopamine receptors, but also on cardiac adrenergic receptors. We will discuss the utility of drugs that are currently available as tools to understand cardiac dopamine receptors. The molecule dopamine itself is present in the mammalian heart. Therefore, cardiac dopamine might act as an autocrine or paracrine compound in the mammalian heart. Dopamine itself might cause cardiac diseases. Moreover, the cardiac function of dopamine and the expression of dopamine receptors in the heart can be altered in diseases such as sepsis. Various drugs for cardiac and non-cardiac diseases are currently in the clinic that are, at least in part, agonists or antagonists at dopamine receptors. We define the research needs in order to understand dopamine receptors in the heart better. All in all, an update on the role of dopamine receptors in the human heart appears to be clinically relevant, and is thus presented here.

Sorting nexins: role in the regulation of blood pressure

Sorting nexins (SNXs) are a family of proteins that regulate cellular cargo sorting and trafficking, maintain intracellular protein homeostasis, and participate in intracellular signaling. SNXs are also important in the regulation of blood pressure via several mechanisms. Aberrant expression and dysfunction of SNXs participate in the dysregulation of blood pressure. Genetic studies show a correlation between SNX gene variants and the response to antihypertensive drugs. In this review, we summarize the progress in SNX-mediated regulation of blood pressure, discuss the potential role of SNXs in the pathophysiology and treatment of hypertension, and propose novel strategies for the medical therapy of hypertension.

Effect of D4 Dopamine Receptor on Na+-K+-ATPase Activity in Renal Proximal Tubule Cells

Dopamine, via its receptors, plays a vital role in the maintenance of blood pressure by modulating renal sodium transport. However, the role of the D₄ dopamine receptor (D₄ receptor) in renal proximal tubules (PRTs) is still unclear. This study aimed to verify the hypothesis that activation of D₄ receptor directly inhibits the activity of the Na⁺-K⁺-ATPase (NKA) in RPT cells.

Methods

NKA activity, nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) levels were measured in RPT cells treated with the D₄ receptor agonist PD168077 and/or the D₄ receptor antagonist L745870, the NO synthase inhibitor NG-nitro-L-arginine-methyl ester (L-NAME) or the soluble guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo-[4,3-a] quinoxalin-1-one (ODQ). Total D₄ receptor expression and its expression in the plasma membrane were investigated by immunoblotting in RPT cells from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs).

Results

Activation of D₄ receptors with PD168077, inhibited NKA activity in RPT cells from WKY rats in a concentration- and time-dependent manner. The inhibitory effect of PD168077 on NKA activity was prevented by the addition of the D₄ receptor antagonist L745870, which by itself had no effect. The NO synthase inhibitor L-NAME and the soluble guanylyl cyclase inhibitor ODQ, which by themselves had no effect on NKA activity, eliminated the inhibitory effect of PD168077 on NKA activity. Activation of D₄ receptors also increased NO levels in the culture medium and cGMP levels in RPT cells. However, the inhibitory effect of D₄ receptors on NKA activity was absent in RPT cells from SHRs, which could be related to decreased plasma membrane expression of D₄ receptors in SHR RPT cells.

Conclusions

Activation of D₄ receptors directly inhibits NKA activity via the NO/cGMP signaling pathway in RPT cells from WKY rats but not SHRs. Aberrant regulation of NKA activity in RPT cells may be involved in the pathogenesis of hypertension.

Interactions between the intrarenal dopaminergic and the renin-angiotensin systems in the control of systemic arterial pressure

Systemic arterial hypertension is one of the leading causes of morbidity and mortality in the general population, being a risk factor for many cardiovascular diseases. Although its pathogenesis is complex and still poorly understood, some systems appear to play major roles in its development. This review aims to update the current knowledge on the interaction of the intrarenal renin-angiotensin system (RAS) and dopaminergic system in the development of hypertension, focusing on recent scientific hallmarks in the field. The intrarenal RAS, composed of several peptides and receptors, has a critical role in the regulation of blood pressure (BP) and, consequently, the development of hypertension. The RAS is divided into two main intercommunicating axes: the classical axis, composed of angiotensin-converting enzyme, angiotensin II, and angiotensin type 1 receptor, and the ACE2/angiotensin-(1-7)/Mas axis, which appears to modulate the effects of the classical axis. Dopamine and its receptors are also increasingly showing an important role in the pathogenesis of hypertension, as abnormalities in the intrarenal dopaminergic system impair the regulation of renal sodium transport, regardless of the affected dopamine receptor subtype. There are five dopamine receptors, which are divided into two major subtypes: the D1-like (D1R and D5R) and D2-like (D2R, D3R, and D4R) receptors. Mice deficient in any of the five dopamine receptor subtypes have increased BP. Intrarenal RAS and the dopaminergic system have complex interactions. The balance between both systems is essential to regulate the BP homeostasis, as alterations in the control of both can lead to hypertension.

Inverse Salt Sensitivity of Blood Pressure: Mechanisms and Potential Relevance for Prevention of Cardiovascular Disease

PURPOSE OF REVIEW

To review the etiology of inverse salt sensitivity of blood pressure (BP).

RECENT FINDINGS

Both high and low sodium (Na⁺) intake can be associated with increased BP and cardiovascular morbidity and mortality. However, little is known regarding the mechanisms involved in the increase in BP in response to low Na⁺ intake, a condition termed inverse salt sensitivity of BP, which affects approximately 15% of the adult population. The renal proximal tubule is important in regulating up to 70% of renal Na⁺ transport. The renin-angiotensin and renal dopaminergic systems play both synergistic and opposing roles in the regulation of Na⁺ transport in this nephron segment. Clinical studies have demonstrated that individuals express a "personal salt index" (PSI) that marks whether they are salt-resistant, salt-sensitive, or inverse salt-sensitive. Inverse salt sensitivity results in part from genetic polymorphisms in various Na⁺ regulatory genes leading to a decrease in natriuretic activity and an increase in renal tubular Na⁺ reabsorption leading to an increase in BP. This article reviews the potential mechanisms of a new pathophysiologic entity, inverse salt sensitivity of BP, which affects approximately 15% of the general adult population.

The dopamine receptor D4 regulates the proliferation of pulmonary arteries smooth muscle in broilers by downregulating AT1R

The major cause of pulmonary vascular remodeling in broilers is abnormal proliferation of vascular smooth muscle cells (VSMCs), and one of the main causes of pulmonary hypertension syndrome (PHS) in broilers is pulmonary artery vascular remodeling. Forty Arbor Acres (AA) broilers were randomly divided into four groups (n = 10): a control group (deionized water, 0 g/L NaCl), a freshwater group (FW, deionized water + 1 g/L NaCl), highly salinized freshwater group 1 (H-SFW-1, deionized water + 2.5 g/L NaCl) and highly salinized freshwater group 2 (H-SFW-2, deionized water + 5 g/L NaCl). The results of in vivo experiments showed that vascular smooth muscle of the broilers could be significantly proliferated by intake of high-salinity fresh water (H-SFW-1 & H-SFW-2), which significantly increased the content of angiotensin II (Ang II) and the expression of angiotensin II type 1 (AT1) receptor protein. Meanwhile, it significantly decreased the expression of dopamine receptor D4 (DRD4) protein. The results of in vitro experiments showed that exogenous Ang II induced the proliferation of primary VSMCs in broilers, which could be significantly inhibited by DRD4 agonists (D4A, HY-101384A) and enhanced by DRD4 inhibitors (D4I, HY-B0965). In addition, the results of immunoblotting and fluorescence quantitative PCR showed that AT1 receptors could be negatively regulated by DRD4 in VSMCs of broilers, either at the transcriptional or translational level. At the same time, the expression of AT1 receptor could be increased by DRD4 inhibition by D4I and decreased by DRD4 activation by D4A. The negative regulatory effect of DRD4 on AT1 receptor occurred in a dose-dependent manner. These results indicate that long-term intake of highly salinized fresh water can cause PHS in broilers, accompanied by varying degrees of proliferation of pulmonary artery smooth muscle. This mechanism may involve response of its receptor being induced by increased Ang II, while DRD4 can negatively regulate it.

DRD4 (Dopamine D4 Receptor) Mitigate Abdominal Aortic Aneurysm via Decreasing P38 MAPK (mitogen-activated protein kinase)/NOX4 (NADPH Oxidase 4) Axis-Associated Oxidative Stress

[Figure: see text].

Renal Dopamine Receptors and Oxidative Stress: Role in Hypertension

Significance: The kidney plays an important role in the long-term control of blood pressure. Oxidative stress is one of the fundamental mechanisms responsible for the development of hypertension. Dopamine, via five subtypes of receptors, plays an important role in the control of blood pressure by various mechanisms, including the inhibition of oxidative stress. Recent Advances: Dopamine receptors exert their regulatory function to decrease the oxidative stress in the kidney and ultimately maintain normal sodium balance and blood pressure homeostasis. An aberration of this regulation may be involved in the pathogenesis of hypertension. Critical Issues: Our present article reviews the important role of oxidative stress and intrarenal dopaminergic system in the regulation of blood pressure, summarizes the current knowledge on renal dopamine receptor-mediated antioxidation, including decreasing reactive oxygen species production, inhibiting pro-oxidant enzyme nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase, and stimulating antioxidative enzymes, and also discusses its underlying mechanisms, including the increased activity of G protein-coupled receptor kinase 4 (GRK4) and abnormal trafficking of renal dopamine receptors in hypertensive status. Future Directions: Identifying the mechanisms of renal dopamine receptors in the regulation of oxidative stress and their contribution to the pathogenesis of hypertension remains an important research focus. Increased understanding of the role of reciprocal regulation between renal dopamine receptors and oxidative stress in the regulation of blood pressure may give us novel insights into the pathogenesis of hypertension and provide a new treatment strategy for hypertension.

Dopamine Receptors and the Kidney: An Overview of Health- and Pharmacological-Targeted Implications

The dopaminergic system can adapt to the different physiological or pathological situations to which the kidneys are subjected throughout life, maintaining homeostasis of natriuresis, extracellular volume, and blood pressure levels. The role of renal dopamine receptor dysfunction is clearly established in the pathogenesis of essential hypertension. Its associations with other pathological states such as insulin resistance and redox balance have also been associated with dysfunction of the dopaminergic system. The different dopamine receptors (D1-D5) show a protective effect against hypertension and kidney disorders. It is essential to take into account the various interactions of the dopaminergic system with other elements, such as adrenergic receptors. The approach to therapeutic strategies for essential hypertension must go through the blocking of those elements that lead to renal vasoconstriction or the restoration of the normal functioning of dopamine receptors. D1-like receptors are fundamental in this role, and new therapeutic efforts should be directed to the restoration of their functioning in many patients. More studies will be needed to allow the development of drugs that can be targeted to renal dopamine receptors in the treatment of hypertension.

The Role of the Renal Dopaminergic System and Oxidative Stress in the Pathogenesis of Hypertension

The kidney is critical in the long-term regulation of blood pressure. Oxidative stress is one of the many factors that is accountable for the development of hypertension. The five dopamine receptor subtypes (D₁R–D₅R) have important roles in the regulation of blood pressure through several mechanisms, such as inhibition of oxidative stress. Dopamine receptors, including those expressed in the kidney, reduce oxidative stress by inhibiting the expression or action of receptors that increase oxidative stress. In addition, dopamine receptors stimulate the expression or action of receptors that decrease oxidative stress. This article examines the importance and relationship between the renal dopaminergic system and oxidative stress in the regulation of renal sodium handling and blood pressure. It discusses the current information on renal dopamine receptor-mediated antioxidative network, which includes the production of reactive oxygen species and abnormalities of renal dopamine receptors. Recognizing the mechanisms by which renal dopamine receptors regulate oxidative stress and their degree of influence on the pathogenesis of hypertension would further advance the understanding of the pathophysiology of hypertension.

Antihypertensive effect of etamicastat in dopamine D2 receptor-deficient mice

Abnormalities of the D₂R gene (DRD2) play a role in the pathogenesis of human essential hypertension; variants of the DRD2 have been reported to be associated with hypertension. Disruption of Drd2 (D₂^-/-) in mice increases blood pressure. The hypertension of D₂^-/- mice has been related, in part, to increased sympathetic activity, renal oxidative stress, and renal endothelin B receptor (ETBR) expression. We tested in D₂^-/- mice the effect of etamicastat, a reversible peripheral inhibitor of dopamine-β-hydroxylase that reduces the biosynthesis of norepinephrine from dopamine and decreases sympathetic nerve activity. Blood pressure was measured in anesthetized D₂^-/- mice treated with etamicastat by gavage, (10 mg/kg), conscious D₂^-/- mice, and D₂^+/+ littermates, and mice with the D₂R selectively silenced in the kidney, treated with etamicastat in the drinking water (10 mg/kg per day). Tissue and urinary catecholamines and renal expression of selected G protein-coupled receptors, enzymes related to the production of reactive oxygen species, and sodium transporters were also measured. Etamicastat decreased blood pressure both in anesthetized and conscious D₂^-/- mice and mice with renal-selective silencing of D₂R to levels similar or close to those measured in D₂^+/+ littermates. Etamicastat decreased cardiac and renal norepinephrine and increased cardiac and urinary dopamine levels in D₂^-/- mice. It also normalized the increased renal protein expressions of ETBR, NADPH oxidase isoenzymes, and urinary 8-isoprostane, as well as renal NHE3 and NCC, and increased the renal expression of D₁R but not D₅R in D₂^-/- mice. In conclusion, etamicastat is effective in normalizing the increased blood pressure and some of the abnormal renal biochemical alterations of D₂^-/- mice.

Effects of dopamine receptor antagonist antipsychotic therapy on blood pressure

WHAT IS KNOWN AND OBJECTIVE

Hypertension, a major risk factor for adverse cardiovascular events, such as stroke and myocardial infarction, affects 80 million American adults. The aetiology of hypertension is multifaceted and difficult to identify. Dopamine receptors, especially those in the kidneys, play a role in blood pressure regulation, and alterations in their function can cause hypertension. The objective of this review was to investigate the association between the use of dopamine antagonists with hypertension focusing especially on second-generation antipsychotics, like clozapine that is D4 receptor antagonist.

METHODS

A literature review was conducted using MEDLINE, Ovid, Science Direct, Web of Science and Cochrane Database of Systematic Reviews databases with keywords:hypertension, hypotension, renin-angiotensin-aldosterone system, dopaminergic receptors, blood pressure, antipsychotics. Inclusion criteria were human or animal studies, systematic reviews, meta-analyses, randomized controlled trials, case report/series, published in selected for inclusion.

RESULTS AND DISCUSSION

All 5 dopamine receptor subtypes (ie D1, D2, D3, D4 and D5) regulate sodium excretion and BP. The D1, D3 and D4 receptors interact directly with the renin-angiotensin-aldosterone system, whereas D2 and D5 receptors directly interact with the sympathetic nervous system to regulate BP. Use of dopaminergic agonists or antagonists could therefore disturb the regulation of BP by dopamine receptors.

WHAT IS NEW AND CONCLUSION

Based upon this review, individuals on antipsychotic agents, particularly clozapine, should be routinely monitored for hypertension, and addition of antihypertensive agents such as angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) is indicated if hypertension occurs.

Effect of D3 dopamine receptor on dopamine D4 receptor expression and function in renal proximal tubule cells from Wistar-Kyoto rats and spontaneously hypertensive rats

BACKGROUND

Dopamine receptors induce natriuresis in kidney. Previous studies have shown interactions between different subtypes of dopamine receptors in renal proximal tubule (RPT) cells. We hypothesize that D3 receptors have an interaction with D4 receptors in RPT cells from normotensive rats (Wistar-Kyoto, WKY) and spontaneously hypertensive rats (SHRs).

METHODS

Immunoblotting and reverse transcriptase-polymerase chain reaction (RT-PCR) were used to examine the expression of D3 and D4 receptors. Na-K-ATPase activity was used to measure the function of receptors. The distribution and colocalization of D3 and D4 receptors were detected by confocal microscopy and co-immunoprecipitation.

RESULTS

D3 receptor agonist PD128907 increased the mRNA and protein expression of D4 receptors in RPT cells from WKY rats, but decreased that from SHRs. In the presence of PLC blocker (U73122, 10-mol/l) or PKC inhibitor 19 -31 (10-mol/l), the up-regulation of D3 receptor on D4 receptor was lost in WKY cells. Moreover, stimulation with PD128907 for 30 minutes decreased D4 receptor degradation in WKY cells, not in SHR cells. D3 and D4 receptors colocalized and co-immunoprecipitated in RPT cells. PD128907 increased co-immunoprecipitation of D3 and D4 receptors in WKY RPT cells, but not in SHR RPT cells. Pre-treatment with D3 receptor agonist also increases D4 receptor mediated inhibitory effect on Na-K-ATPase activity in WKY cells, but not in SHR cells.

CONCLUSION

Renal D3 receptor regulates the expression and function of D4 receptor in RPT cells via PLC /PKC signaling pathway, the loss of this interaction might be involved in the pathogenesis of hypertension.

Blood Pressure and Heart Rate Changes During Clozapine Treatment

People with schizophrenia are 3-4 times more likely to die from cardiovascular disease than the general population. Clozapine (CLZ) is the gold standard of treatment for refractory schizophrenia. It has been associated with tachycardia and recent evidence shows individuals prescribed CLZ may develop blood pressure (BP) elevation and hypertension. The purpose of this study was to examine the effects of CLZ on BP and heart rate (HR). This was a retrospective chart review of patients 18-75 years old with a DSM IV diagnosis of Schizophrenia or Schizoaffective disorder. Primary outcomes were systolic blood pressure (SBP), diastolic blood pressure (DBP), and HR measured 12 weeks before and 24 weeks during CLZ treatment. Eighteen patient records were included in this study. The mean stabilized CLZ dose was 441.7 ± 171.8 mg/day. DBP (t = 1.02, df = 79.5, = 2.00, 0.049) and HR (t = 1.32, df = 355  = -4.61, < 0.0001) were significantly higher after CLZ initiation. A trend was noted for increase in SBP (p = 0.071). 22 % of patients met criteria for hypertension before CLZ and 67 % during CLZ treatment (Chi Square = 6.25, df = 1, p = 0.0124). No significant changes in weight or renal function occured during CLZ treatment. No patients had evidence of cardiomyopathy. The data suggest CLZ may be associated with a rise in BP and HR. The results of this study support previous literature that found an increase in SBP/DBP regardless of CLZ dose, occurring early in treatment. Due to high risk of cardiovascular morbidity and mortality, more work is needed to determine risk factors and understand the mechanism of action that may cause this side effect.

Enhanced hemodynamic responses to angiotensin II in diabetes are associated with increased expression and activity of AT1 receptors in the afferent arteriole

The prevalence of hypertension is about twofold higher in diabetic than in nondiabetic subjects. Hypertension aggravates the progression of diabetic complications, especially diabetic nephropathy. However, the mechanisms for the development of hypertension in diabetes have not been elucidated. We hypothesized that enhanced constrictive responsiveness of renal afferent arterioles (Af-Art) to angiotensin II (ANG II) mediated by ANG II type 1 (AT1) receptors contributes to the development of hypertension in diabetes. In response to an acute bolus intravenous injection of ANG II, alloxan-induced diabetic mice exhibited a higher mean arterial pressure (MAP) (119.1 ± 3.8 vs. 106.2 ± 3.5 mmHg) and a lower renal blood flow (0.25 ± 0.07 vs. 0.52 ± 0.14 ml/min) compared with nondiabetic mice. In response to chronic ANG II infusion, the MAP measured with telemetry increased by 55.8 ± 6.5 mmHg in diabetic mice, but only by 32.3 ± 3.8 mmHg in nondiabetic mice. The mRNA level of AT1 receptor increased by ~10-fold in isolated Af-Art of diabetic mice compared with nondiabetic mice, whereas ANG II type 2 (AT2) receptor expression did not change. The ANG II dose-response curve of the Af-Art was significantly enhanced in diabetic mice. Moreover, the AT1 receptor antagonist, losartan, blocked the ANG II-induced vasoconstriction in both diabetic mice and nondiabetic mice. In conclusion, we found enhanced expression of the AT1 receptor and exaggerated response to ANG II of the Af-Art in diabetes, which may contribute to the increased prevalence of hypertension in diabetes.

Activation of angiotensin II type 1 receptors increases D4 dopamine receptor expression in rat renal proximal tubule cells

Both the dopaminergic and renin-angiotensin systems play important roles in the regulation of blood pressure. Our previous study showed that the stimulation of dopaminergic D₄ receptors reduced angiotensin II type 1 (AT₁) receptor expression in renal proximal tubule (RPT) cells. In this study, we tested whether AT₁ receptors, in return, would regulate D₄ receptor expression and function in RPT cells. Expression of the D₄ receptor from Wistar-Kyoto (WKY) or spontaneously hypertensive rats (SHRs) RPT cells and renal cortex tissues were determined by western blot, and Na⁺-K⁺ ATPase activity was determined using an enzyme assay. Urine volume and urine sodium of WKY rats and SHRs treated with or without D₄ receptor stimulation were measured. Thus, activation of AT₁ receptors with angiotensin II (Ang II) increased D₄ receptor protein expression in RPT cells, and this increase was blocked by nicardipine, a calcium influx blocker. The D₄ receptor agonist PD168077 inhibited Na⁺-K⁺ ATPase activity in WKY RPT cells but not in SHR RPT cells. Ang II pre-treatment promoted D₄ receptor-mediated inhibition of Na⁺-K⁺ ATPase in RPT cells in WKY rats but not in SHRs. Meanwhile, Ang II pre-treatment augmented the natriuretic effect of PD168077 in WKY rats but not in SHRs. In conclusion, AT₁ stimulation can regulate the expression and natriuretic function of dopaminergic D₄ receptors in RPT cells and might be involved in the pathogenesis of essential hypertension.

Therapeutic efficacy of phentolamine in the management of severe hand, foot and mouth disease combined with pulmonary edema

The aim of this study was to examine the effects of phentolamine on severe hand, foot and mouth disease (HFMD) combined with pulmonary edema (PE). From May 2008 to December 2012, 53 children with severe HFMD plus PE were enrolled in the treatment group, receiving phentolamine intravenously at a loading dose of 5 µg/kg/min. The control group comprised 52 children with the same disease who did not receive phentolamine infusion. Data concerning creatine kinase (CK), CK-MB, cardiac troponin I (cTnI), heart rate, systolic blood pressure (SBP) and the duration of ventilation dependence and hospitalization were collected. Adverse events were also recorded. It was found that the phentolamine-treated patients exhibited significantly lower CK, CK-MB and cTnI levels, heart rate and SBP than the controls (P<0.01 for all parameters). The average duration of ventilator dependence and hospitalization was significantly shorter (P<0.01) in the phentolamine group than in the control group. It was also found that the overall mortality rate was lower in the phentolamine group (5.8%) than in the control group (11.5%). No adverse events were observed in either group. Thus, these results offer preliminary evidence that phentolamine reduces mortality and relieves the symptoms of EV71-induced PE. Phentolamine is a potential therapeutic agent for this highly lethal disorder.

Kidney tubules: intertubular, vascular, and glomerular cross-talk

PURPOSE OF REVIEW

The kidney mediates the excretion or conservation of water and electrolytes in the face of changing fluid and salt intake and losses. To ultrafilter and reabsorb the exact quantities of free water and salts to maintain euvolemia a range of endocrine, paracrine, and hormonal signaling systems have evolved linking the tubules, capillaries, glomeruli, arterioles, and other intrinsic cells of the kidney. Our understanding of these systems remains incomplete.

RECENT FINDINGS

Recent work has provided new insights into the workings of the communication pathways between tubular segments and the glomeruli and vasculature, with novel therapeutic agents in development. Particular progress has also been made in the visualization of tubuloglomerular feedback.

SUMMARY

The review summarizes our current understanding of pathway functions in health and disease, as well as future therapeutic options to protect the healthy and injured kidney.

Enhanced Natriuresis and Diuresis in Wistar Rats Caused by the Costimulation of Renal Dopamine D3 and Angiotensin II Type 2 Receptors

BACKGROUND

The kidney, via its regulation of sodium excretion, which is modulated by humoral factors, including the dopamine and renin-angiotensin systems, keeps the blood pressure in the normal range. We have reported a negative interaction between dopamine D3 and AT1 receptors (D3R and AT1R) in renal proximal tubule (RPT) cells. Here, we studied the interaction between D3R and AT2R in vitro and in vivo.

METHODS AND RESULTS

Stimulation of either the D3R or AT2R, by the intrarenal arterial infusion of PD128907, a D3R agonist, or CGP42112A, an AT2R agonist, induced natriuresis and diuresis that were enhanced by the simultaneous infusion of PD128907 and CGP42112A in Wistar rats. The D3/AT2 receptor interaction was confirmed in in vitro, i.e., stimulation of either the D3R or AT2R inhibited Na(+)-K(+)-ATPase activity that was enhanced by the costimulation of these receptors. D3R and AT2R colocalized and coimmunoprecipitated in kidney and RPT cells (RPTCs). Stimulation of one receptor increased the localization of the other receptor at the plasma cell membrane. ERK1/2-MAPK is involved in the signaling pathway of D3R and AT2R interaction because costimulation of D3R and AT2R significantly increased ERK1/2-MAPK expression in RPTCs; inhibition of ERK1/2-MAPK abolished the inhibition of Na(+)-K(+)-ATPase activity that was enhanced by D3R and AT2R costimulation.

CONCLUSIONS

Our current study indicates that D3R, in combination with AT2R, enhances natriuresis and diuresis, via ERK1/2-MAPK pathway, that may be involved in the regulation of blood pressure.

Activation of the D4 dopamine receptor attenuates proliferation and migration of vascular smooth muscle cells through downregulation of AT1a receptor expression

Angiotensin (Ang) II has an important role in the vascular smooth muscle cell (VSMC) proliferation and migration and subsequently in the development of vascular diseases, whereas dopamine has the opposite effect. Previous studies have shown an interaction between dopamine and AT(1) receptors in the kidney. The dopamine D(4) receptor is expressed in arteries and has an inhibitory effect on VSMC proliferation. We hypothesized that the D(4) receptor, through its interaction with the AT(1a) receptor, may have an inhibitory effect on Ang II-mediated VSMC proliferation and migration, which could have a pivotal role in hypertension-induced vascular remodeling. In the current study, we found that Ang II markedly induced the proliferation and migration of A10 cells, which was inhibited by the D(4) receptor agonist PD168077. The activation of the D(4) receptor by PD168077 inhibited AT(1a) receptor expression in a concentration- and time-dependent manner. These effects were attenuated by silencing the D(4) receptor with a D(4) receptor-targeting small interfering RNA. The D(4) receptor-mediated inhibition of AT(1) receptor function involved protein kinase A (PKA). The activation of the D(4) receptor by PD168077 increased PKA activity in A10 cells, and the presence of a PKA inhibitor (PKA inhibitor 14-22, 10(-7) mol l(-1) per 24 h) blocked the inhibitory effect of the D(4) receptor on AT(1) receptor expression and function. The inhibitory effect of the D(4) receptor on AT(1) receptor expression and function was preserved in VSMCs (primary culture) from spontaneously hypertensive rats relative to VSMCs from Wistar-Kyoto rats. In conclusion, our data provide insight into the regulatory role of the D(4) receptor on AT(1a) receptor expression and function in VSMCs and suggest that targeting the action of the D(4) receptor may represent an effective therapeutic approach for the treatment of cardiovascular diseases.

Activation of D4 dopamine receptor decreases angiotensin II type 1 receptor expression in rat renal proximal tubule cells

The dopaminergic and renin-angiotensin systems interact to regulate blood pressure. Disruption of the D4 dopamine receptor gene in mice produces hypertension that is associated with increased renal angiotensin type 1 (AT1) receptor expression. We hypothesize that the D4 receptor can inhibit AT1 receptor expression and function in renal proximal tubule cells from Wistar-Kyoto (WKY) rats, but the D4 receptor regulation of AT1 receptor is aberrant in renal proximal tubule cells from spontaneously hypertensive rats (SHRs). The D4 receptor agonist, PD168077, decreased AT1 receptor protein expression in a time- and concentration-dependent manner in WKY cells. By contrast, in SHR cells, PD168077 increased AT1 receptor protein expression. The inhibitory effect of D4 receptor on AT1 receptor expression in WKY cells was blocked by a calcium channel blocker, nicardipine, or calcium-free medium, indicating that calcium is involved in the D4 receptor-mediated signaling pathway. Angiotensin II increased Na(+)-K(+) ATPase activity in WKY cells. Pretreatment with PD168077 decreased the stimulatory effect of angiotensin II on Na(+)-K(+) ATPase activity in WKY cells. In SHR cells, the inhibitory effect of D4 receptor on angiotensin II-mediated stimulation of Na(+)-K(+) ATPase activity was aberrant; pretreatment with PD168077 augmented the stimulatory effect of AT1 receptor on Na(+)-K(+) ATPase activity in SHR cells. This was confirmed in vivo; pretreatment with PD128077 for 1 week augmented the antihypertensive and natriuretic effect of losartan in SHRs but not in WKY rats. We suggest that an aberrant interaction between D4 and AT1 receptors may play a role in the abnormal regulation of sodium excretion in hypertension.

Sestrin2 decreases renal oxidative stress, lowers blood pressure, and mediates dopamine D2 receptor-induced inhibition of reactive oxygen species production

The dopamine D2 receptor (D2R) decreases renal reactive oxygen species (ROS) production and regulates blood pressure, in part, via positive regulation of paraoxonase 2. Sestrin2, a highly conserved antioxidant protein, regulates intracellular ROS level by regenerating hyperoxidized peroxiredoxins. We hypothesized that sestrin2 may be involved in preventing excessive renal ROS production and thus contribute to the maintenance of normal blood pressure. Moreover, the D2R may decrease ROS production, in part, through the regulation of sestrin2. Renal sestrin2 expression was lower (-62±13%) in D2R(-/-) than in D2R(+/+) mice. Silencing D2R in human renal proximal tubule cells decreased sestrin2 expression (-53±3%) and increased hyperoxidized peroxiredoxins (2.9-fold). Stimulation of D2R in renal proximal tubule cells increased sestrin2 expression (1.6-fold), decreased hyperoxidized peroxiredoxins (-61±3%), and reduced ROS production (-31±4%). Silencing sestrin2 in renal proximal tubule cells increased hyperoxidized peroxiredoxins (2.1-fold) and ROS production (1.3-fold). Silencing sestrin2 also abolished D2R-induced decrease in peroxiredoxin hyperoxidation and partially prevented the inhibitory effect of D2R stimulation on ROS production. Silencing paraoxonase 2 increased sestrin2 ubiquitinylation (2.8-fold), decreased sestrin2 expression (-30±3%), and increased ROS production (1.3-fold), peroxiredoxin hyperoxidation (2.9-fold), and lipid peroxidation (2.3-fold), and blocked the increase in sestrin2 that occurs with D2R stimulation. In vivo renal selective silencing of sestrin2 by the renal subcapsular infusion of sestrin2 small interfering RNA (3 μg/day; 7 days) in mice increased renal oxidative stress (1.3-fold) and blood pressure. These results suggest that the D2R, via paraoxonase 2 and sestrin2, keeps normal renal redox balance, which contributes to the maintenance of normal blood pressure.

Direct inhibition of basolateral Kir4.1/5.1 and Kir4.1 channels in the cortical collecting duct by dopamine

It is recognized that dopamine promotes natriuresis by inhibiting multiple transporting systems in the proximal tubule. In contrast, less is known about the molecular targets of dopamine actions on water-electrolyte transport in the cortical collecting duct (CCD). Epithelial cells in the CCD are exposed to dopamine, which is synthesized locally or secreted from sympathetic nerve endings. Basolateral K(+) channels in the distal renal tubule are critical for K(+) recycling and controlling basolateral membrane potential to establish the driving force for Na(+) reabsorption. Here, we demonstrate that Kir4.1 and Kir5.1 are highly expressed in the mouse kidney cortex and are localized to the basolateral membrane of the CCD. Using patch-clamp electrophysiology in freshly isolated CCDs, we detected highly abundant 40-pS and scarce 20-pS single channel conductances, most likely representing Kir4.1/5.1 and Kir4.1 channels, respectively. Dopamine reversibly decreased the open probability of both channels, with a relatively greater action on the Kir4.1/5.1 heterodimer. This effect was mediated by D2-like but not D1-like dopamine receptors. PKC blockade abolished the inhibition of basolateral K(+) channels by dopamine. Importantly, dopamine significantly decreased the amplitude of Kir4.1/5.1 and Kir4.1 unitary currents. Consistently, dopamine induced an acute depolarization of basolateral membrane potential, as directly monitored using current-clamp mode in isolated CCDs. Therefore, we demonstrate that dopamine inhibits basolateral Kir4.1/5.1 and Kir4.1 channels in CCD cells via stimulation of D2-like receptors and subsequently PKC. This leads to depolarization of the basolateral membrane and a decreased driving force for Na(+) reabsorption in the distal renal tubule.

Intravital Förster resonance energy transfer imaging reveals elevated [Ca2+]i and enhanced sympathetic tone in femoral arteries of angiotensin II-infused hypertensive biosensor mice

Artery narrowing in hypertension can only result from structural remodelling of the artery, or increased smooth muscle contraction. The latter may occur with, or without, increases in [Ca(2+)]i. Here, we sought to measure, in living hypertensive mice, possible changes in artery dimensions and/or [Ca(2+)]i, and to determine some of the mechanisms involved. Ca(2+)/calmodulin biosensor (Förster resonance energy transfer-based) mice were made hypertensive by s.c. infusion of angiotensin II (Ang II, 400 ng kg(-1) min(-1), 2-3 weeks). Intravital fluorescence microscopy was used to determine [Ca(2+)]i and outer diameter of surgically exposed, intact femoral artery (FA) of anaesthetized mice. Active contractile FA 'tone' was calculated from the basal-state diameter and the passive (i.e. Ca(2+)-free) diameter (PD). Compared to saline control, FAs of Ang II-infused mice had (1) ∼21% higher active tone and (2) ∼78 nm higher smooth muscle [Ca(2+)]i, but (3) the same PDs. The local Ang II receptor (AT1R) blocker losartan had negligible effect on tone or [Ca(2+)]i in control FAs, but reduced the basal tone by ∼9% in Ang II FAs. Both i.v. hexamethonium and locally applied prazosin abolished the difference in FA tone and [Ca(2+)]i, suggesting a dominant role of sympathetic nerve activity (SNA). Changes in diameter and [Ca(2+)]i in response to locally applied phenylephrine, Ang II, arginine vasopressin, elevated [K(+)]o and acetylcholine were not altered. In summary, FAs of living Ang II hypertensive mice have higher [Ca(2+)]i, and are more constricted, due, primarily, to elevated SNA and some increased arterial AT1R activation. Evidence of altered artery reactivity or remodeling was not found.

Renal dopamine receptors, oxidative stress, and hypertension

Dopamine, which is synthesized in the kidney, independent of renal nerves, plays an important role in the regulation of fluid and electrolyte balance and systemic blood pressure. Lack of any of the five dopamine receptor subtypes (D1R, D2R, D3R, D4R, and D5R) results in hypertension. D1R, D2R, and D5R have been reported to be important in the maintenance of a normal redox balance. In the kidney, the antioxidant effects of these receptors are caused by direct and indirect inhibition of pro-oxidant enzymes, specifically, nicotinamide adenine dinucleotide phosphate, reduced form (NADPH) oxidase, and stimulation of anti-oxidant enzymes, which can also indirectly inhibit NADPH oxidase activity. Thus, stimulation of the D2R increases the expression of endogenous anti-oxidants, such as Parkinson protein 7 (PARK7 or DJ-1), paraoxonase 2 (PON2), and heme oxygenase 2 (HO-2), all of which can inhibit NADPH oxidase activity. The D5R decreases NADPH oxidase activity, via the inhibition of phospholipase D2, and increases the expression of HO-1, another antioxidant. D1R inhibits NADPH oxidase activity via protein kinase A and protein kinase C cross-talk. In this review, we provide an overview of the protective roles of a specific dopamine receptor subtype on renal oxidative stress, the different mechanisms involved in this effect, and the role of oxidative stress and impairment of dopamine receptor function in the hypertension that arises from the genetic ablation of a specific dopamine receptor gene in mice.

Dopamine-angiotensin interactions in the basal ganglia and their relevance for Parkinson's disease

Renin-angiotensin systems are known to act in many tissues, for example, the blood vessel wall or kidney, where a close interaction between angiotensin and dopamine has been demonstrated. Regulatory interactions between the dopaminergic and renin-angiotensin systems have recently been described in the substantia nigra and striatum. In animal models, dopamine depletion induces compensatory overactivation of the local renin-angiotensin system, which primes microglial responses and neuron vulnerability by activating NADPH-oxidase. Hyperactivation of the local renin-angiotensin system exacerbates the inflammatory microglial response, oxidative stress, and dopaminergic degeneration, all of which are inhibited by angiotensin receptor blockers and inhibitors of angiotensin-converting enzymes. In this review we provide evidence suggesting that the renin-angiotensin system may play an important role in dopamine's mediated neuroinflammation and oxidative stress changes in Parkinson's disease. We suggest that manipulating brain angiotensin may constitute an effective neuroprotective strategy for Parkinson's disease.

Upregulation of renal D5 dopamine receptor ameliorates the hypertension in D3 dopamine receptor-deficient mice

D3 dopamine receptor (D3R)-deficient mice have renin-dependent hypertension associated with sodium retention, but the hypertension is mild. To determine whether any compensatory mechanisms in the kidney are involved in the regulation of blood pressure with disruption of Drd3, we measured the renal protein expression of all dopamine receptor subtypes (D1R, D2R, D4R, and D5R) in D3R homozygous (D3(-/-)) and heterozygous (D3(+/-)) knockout mice and their wild-type (D3(+/+)) littermates. The renal immunohistochemistry and protein expression of D5R were increased (n=5/group) in D3(-/-) mice; renal D4R protein expression was decreased, whereas renal protein expressions of D1R and D2R were similar in both groups. Renal D5R protein expression was also increased in D3(+/-) (n=5/group) relative to D3(+/+) mice, whereas D1R, D2R, and D4R protein expressions were similar in D3(+/-) and D3(+/+) mice. The increase in renal D5R protein expression was abolished when D3(-/-) mice were fed a high-salt diet. Treatment with the D1-like receptor antagonist, SCH23390, increased the blood pressure in anesthetized D3(-/-) but not D3(+/+) mice (n=4/group), suggesting that the renal upregulation of D5R may have minimized the hypertension in D3(-/-) mice. The renal D5R protein upregulation was not caused by increased transcription because renal mRNA expression of D5R was similar in D3(-/-) and D3(+/+) mice. Our findings suggest that the renal upregulation of D5R may have minimized the hypertension that developed in D3(-/-) mice.

D5 dopamine receptor decreases NADPH oxidase, reactive oxygen species and blood pressure via heme oxygenase-1

D5 dopamine receptor (D5R) knock-out mice (D5(-/-)) have a higher blood pressure (BP) and higher reactive oxygen species (ROS) production than their D5R wild-type littermates (D5(+/+)). We tested the hypothesis that the high BP and increased ROS production in D5(-/-) mice may be caused by decreased heme oxygenase-1 (HO-1) expression and activity. We found that renal HO-1 protein expression and HO enzyme activity were decreased (65 and 50%, respectively) in D5(-/-) relative to D5(+/+) mice. A 24 h of administration of hemin, an HO-1 inducer, increased HO-1 expression and HO activity (6.8- and 1.9-fold, respectively) and normalized the increased ROS production and BP in D5(-/-) mice. Expression of HO-1 protein and HO activity were increased (2.3- and 1.5-fold, respectively) in HEK cells that heterologously expressed human wild-type D5R (HEK-hD5R), but not the empty vector-transfected HEK-293 cells. Fenoldopam (Fen), a D5R agonist, increased HO activity (3 h), HO-1 protein expression, HO-1 and D5R colocalization and co-immunoprecipitation in HEK-hD5R cells. Cellular NADPH oxidase activity was decreased by 35% in HEK-hD5R that was abrogated with silencing of the heme oxygenase 1 gene (HMOX1). HMOX1 siRNA also impaired the ability of Fen to decrease NADPH oxidase activity in HEK-hD5R cells. In summary, the D5R positively regulates HO-1 through direct protein/protein interaction in the short-term and by increasing HO-1 protein expression in the long-term. The impaired D5R regulation of HO-1 and ROS production contributes to the pathogenesis of hypertension in D5(-/-) mice.

Chronic regulation of the renal Na(+)/H(+) exchanger NHE3 by dopamine: translational and posttranslational mechanisms

The intrarenal autocrine/paracrine dopamine (DA) system contributes to natriuresis in response to both acute and chronic Na(+) loads. While the acute DA effect is well described, how DA induces natriuresis chronically is not known. We used an animal and a cell culture model to study the chronic effect of DA on a principal renal Na(+) transporter, Na(+)/H(+) exchanger-3 (NHE3). Intraperitoneal injection of Gludopa in rats for 2 days elevated DA excretion and decreased total renal cortical and apical brush-border NHE3 antigen. Chronic treatment of an opossum renal proximal cell line with DA decreased NHE3 activity, cell surface and total cellular NHE3 antigen, but not NHE3 transcript. The decrease in NHE3 antigen was dose and time dependent with maximal inhibition at 16-24 h and half maximal effect at 3 × 10(-7) M. This is in contradistinction to the acute effect of DA on NHE3 (half maximal at 2 × 10(-6) M), which was not associated with changes in total cellular NHE3 protein. The DA-induced decrease in total NHE3 protein was associated with decrease in NHE3 translation and mediated by cis-sequences in the NHE3 5'-untranslated region. DA also decreased cell surface and total cellular NHE3 protein half-life. The DA-induced decrease in total cellular NHE3 was partially blocked by proteasome inhibition but not by lysosome inhibition, and DA increased ubiquitylation of total and surface NHE3. In summary, chronic DA inhibits NHE3 with mechanisms distinct from its acute action and involves decreased NHE3 translation and increased NHE3 degradation, which are novel mechanisms for NHE3 regulation.

Paraoxonase 2 decreases renal reactive oxygen species production, lowers blood pressure, and mediates dopamine D2 receptor-induced inhibition of NADPH oxidase

The dopamine D(2) receptor (D(2)R) regulates renal reactive oxygen species (ROS) production, and impaired D(2)R function results in ROS-dependent hypertension. Paraoxonase 2 (PON2), which belongs to the paraoxonase gene family, is expressed in various tissues, acting to protect against cellular oxidative stress. We hypothesized that PON2 may be involved in preventing excessive renal ROS production and thus may contribute to maintenance of normal blood pressure. Moreover, D(2)R may decrease ROS production, in part, through regulation of PON2. D(2)R colocalized with PON2 in the brush border of mouse renal proximal tubules. Renal PON2 protein was decreased (-33±6%) in D(2)(-/-) relative to D(2)(+/+) mice. Renal subcapsular infusion of PON2 siRNA decreased PON2 protein expression (-55%), increased renal oxidative stress (2.2-fold), associated with increased renal NADPH oxidase expression (Nox1, 1.9-fold; Nox2, 2.9-fold; and Nox4, 1.6-fold) and activity (1.9-fold), and elevated arterial blood pressure (systolic, 134±5 vs 93±6mmHg; diastolic, 97±4 vs 65±7mmHg; mean 113±4 vs 75±7mmHg). To determine the relevance of the PON2 and D(2)R interaction in humans, we studied human renal proximal tubule cells. Both D(2)R and PON2 were found in nonlipid and lipid rafts and physically interacted with each other. Treatment of these cells with the D(2)R/D(3)R agonist quinpirole (1μM, 24h) decreased ROS production (-35±6%), associated with decreased NADPH oxidase activity (-32±3%) and expression of Nox2 (-41±7%) and Nox4 (-47±8%) protein, and increased expression of PON2 mRNA (2.1-fold) and protein (1.6-fold) at 24h. Silencing PON2 (siRNA, 10nM, 48h) not only partially prevented the quinpirole-induced decrease in ROS production by 36%, but also increased basal ROS production (1.3-fold), which was associated with an increase in NADPH oxidase activity (1.4-fold) and expression of Nox2 (2.1-fold) and Nox4 (1.8-fold) protein. Inhibition of NADPH oxidase with diphenylene iodonium (10μM/30 min) inhibited the increase in ROS production caused by PON2 silencing. Our results suggest that renal PON2 is involved in the inhibition of renal NADPH oxidase activity and ROS production and contributes to the maintenance of normal blood pressure. PON2 is positively regulated by D(2)R and may, in part, mediate the inhibitory effect of renal D(2)R on NADPH oxidase activity and ROS production.

Between candidate genes and whole genomes: time for alternative approaches in blood pressure genetics

Blood pressure has a significant genetic component, but less than 3% of the observed variance has been attributed to genetic variants identified to date. Candidate gene studies of rare, monogenic hypertensive syndromes have conclusively implicated several genes altering renal sodium balance, and studies of essential hypertension have inconsistently implicated over 50 genes in pathways affecting renal sodium balance and other functions. Genome-wide linkage scans have replicated numerous quantitative trait loci throughout the genome, and over 50 single nucleotide polymorphisms (SNPs) have been replicated in multiple genome-wide association studies. These studies provide considerable evidence that epistasis and other interactions play a role in the genetic architecture of blood pressure regulation, but candidate gene studies have limited scope to test for epistasis, and genome-wide studies have low power for both main effects and interactions. This review summarizes the genetic findings to date for blood pressure, and it proposes focused, pathway-based approaches involving epistasis, gene-environment interactions, and next-generation sequencing to further the genetic dissection of blood pressure and hypertension.

Dopamine and renal function and blood pressure regulation

Dopamine is an important regulator of systemic blood pressure via multiple mechanisms. It affects fluid and electrolyte balance by its actions on renal hemodynamics and epithelial ion and water transport and by regulation of hormones and humoral agents. The kidney synthesizes dopamine from circulating or filtered L-DOPA independently from innervation. The major determinants of the renal tubular synthesis/release of dopamine are probably sodium intake and intracellular sodium. Dopamine exerts its actions via two families of cell surface receptors, D1-like receptors comprising D1R and D5R, and D2-like receptors comprising D2R, D3R, and D4R, and by interactions with other G protein-coupled receptors. D1-like receptors are linked to vasodilation, while the effect of D2-like receptors on the vasculature is variable and probably dependent upon the state of nerve activity. Dopamine secreted into the tubular lumen acts mainly via D1-like receptors in an autocrine/paracrine manner to regulate ion transport in the proximal and distal nephron. These effects are mediated mainly by tubular mechanisms and augmented by hemodynamic mechanisms. The natriuretic effect of D1-like receptors is caused by inhibition of ion transport in the apical and basolateral membranes. D2-like receptors participate in the inhibition of ion transport during conditions of euvolemia and moderate volume expansion. Dopamine also controls ion transport and blood pressure by regulating the production of reactive oxygen species and the inflammatory response. Essential hypertension is associated with abnormalities in dopamine production, receptor number, and/or posttranslational modification.

Fasting-induced reductions in cardiovascular and metabolic variables occur sooner in obese versus lean mice

It is not uncommon for laboratory animals to be fasted prior to experimentation. Fasting evokes marked reductions in heart rate (HR), blood pressure (BP), heat production and oxygen consumption (VO(2)) in rodents. Mice with diet-induced obesity exhibit elevated HR and BP, and lower VO(2) and heat production in the fed condition versus their lean counterparts. It is unknown whether body composition alters the tempo of response to fasting. We tested the hypothesis that cardiovascular and metabolic responses to fasting are delayed in obese versus lean male C57BL/6J mice. In the fed condition, mice that consumed high-fat (HF, 45% fat) chow for 98 ± 5 days had elevated (P < 0.05) body fat percentage (DEXA), serum leptin (ELISA), HR and BP (72-h biotelemetry), and lower (P < 0.05) heat production and VO(2) (72-h metabolic chamber) versus animals that consumed standard chow (CON, 10% fat; n = 16 per group). HR, BP, VO(2), heat production and serum leptin decreased (all P < 0.05) in response to a 16-h fast (16:00-08:00 h) in both groups. Although the overall fold changes in cardiovascular and metabolic parameters were similar in magnitude among animals, fasting-induced reductions in cardiovascular and metabolic variables occurred ∼4 and ∼7 h earlier (P < 0.05), respectively, in HF versus CON mice. These findings indicate that while metabolic and cardiovascular stress evoked by a 16-h fast at 22°C is not different between HF and CON mice, fasting-induced responses occur sooner in obese animals.

Upregulation of renal sodium transporters in D5 dopamine receptor-deficient mice

D(5) dopamine receptor (D(5)R)-deficient (D(5)(-/-)) mice have hypertension that is aggravated by an increase in sodium intake. The present experiments were designed to test the hypothesis that a dysregulation of renal sodium transporters is related to the salt sensitivity in D(5)(-/-) mice. D(5)R was expressed in the renal proximal tubule, thick ascending limb, distal convoluted tubule, and cortical and outer medullary collecting ducts in D(5)(+/+) mice. On a control Na(+) diet, renal protein expressions of NKCC2 (sodium-potassium-2 chloride cotransporter), sodium chloride cotransporter, and alpha and gamma subunits of the epithelial sodium channel were greater in D(5)(-/-) than in D(5)(+/+) mice. Renal renin abundance and urine aldosterone levels were similar but renal angiotensin II type 1 receptor (AT(1)R) protein expression was increased in D(5)(-/-) mice. An elevated Na(+) diet increased further the elevated blood pressure of D(5)(-/-) mice but did not affect the normal blood pressure of D(5)(+/+) mice. The increased levels of NKCC2, sodium chloride cotransporter, and alpha and gamma subunits of the epithelial sodium channel persisted with the elevated Na(+) diet and unaffected by chronic AT(1)R blockade (losartan) in D(5)(-/-) mice. The expressions of proximal sodium transporters NHE3 (sodium hydrogen exchanger type 3) and NaPi2 (sodium phosphate cotransporter type 2) were increased by the elevated Na(+) diet in D(5)(-/-) mice; the increased expression of NHE3 but not NaPi2 was abolished by AT(1)R blockade. Our findings suggest that the increased protein expression of sodium transporters/channels in distal nephron segments may be the direct consequence of the disruption of D(5)R, independent of the renin-angiotensin aldosterone system.

Acute regulation of renal Na+/H+ exchanger NHE3 by dopamine: role of protein phosphatase 2A

Nephrogenic dopamine is a potent natriuretic paracrine/autocrine hormone that is central for mammalian sodium homeostasis. In the renal proximal tubule, dopamine induces natriuresis partly via inhibition of the sodium/proton exchanger NHE3. The signal transduction pathways and mechanisms by which dopamine inhibits NHE3 are complex and incompletely understood. This manuscript describes the role of the serine/threonine protein phosphatase 2A (PP2A) in the regulation of NHE3 by dopamine. The PP2A regulatory subunit B56δ (coded by the Ppp2r5d gene) directly associates with more than one region of the carboxy-terminal hydrophilic putative cytoplasmic domain of NHE3 (NHE3-cyto), as demonstrated by yeast-two-hybrid, coimmunoprecipitation, blot overlay, and in vitro pull-down assays. Phosphorylated NHE3-cyto is a substrate for purified PP2A in an in vitro dephosphorylation reaction. In cultured renal cells, inhibition of PP2A by either okadaic acid or by overexpression of the simian virus 40 (SV40) small T antigen blocks the ability of dopamine to inhibit NHE3 activity and to reduce surface NHE3 protein. Dopamine-induced NHE3 redistribution is also blocked by okadaic acid ex vivo in rat kidney cortical slices. These studies demonstrate that PP2A is an integral and critical participant in the signal transduction pathway between dopamine receptor activation and NHE3 inhibition.

A real-time, telemetric method for continuous measurement of portal pressures

The ability to longitudinally monitor portal and splanchnic pressures would greatly enhance the understanding of acute and chronic liver disease by helping to assess the immediate and long-term impact of therapeutic manipulations. However, a technique for measuring portal pressures in the ambulatory setting is not currently available. To overcome this difficulty, we utilized an approach that involved the implantation of a miniature telemetric device, equipped with a specially-designed pressure transmission catheter, into the spleen of an anesthetized mouse. Using this approach, portal pressures were measured continuously over 5 d in conscious, unrestrained animals, the availability of which will help facilitate studies of the portal circulation requiring long-term stability.

Molecular and pharmacological detection of dopaminergic receptors in the human male urinary tract

AIMS

Evidence indicates that dopamine (DA) and DA receptors play a role in the central nervous system (CNS) control of micturition; however, while the central DAergic role in the micturition physiology has been extensively investigated, the expression and the function of DA receptors in the urinary tract are still under investigation. Here, we studied the distribution of DA receptor subtypes in different parts of the human male urinary tract.

METHODS

Fragments were collected from 34 men. The mRNAs encoding DA receptors were assessed by RT-PCR, followed by densitometric analysis. Adenylyl cyclase (AC) activity was evaluated using a commercially available RIA kit. Statistical analysis was carried out using one-way ANOVA, with the Bonferroni's post hoc test.

RESULTS

Results obtained indicated that RT-PCR products of D(1), D(4), and D(5) subtypes were obtained in each part studied, while no signal was observed for the D(2) and D(3) receptor subtypes. The pharmacological characterization demonstrated that the expressed DA receptors were linked to AC.

CONCLUSIONS

DA receptors were expressed throughout the human male urinary tract, from the ureter to the prostatic urethra. In particular, we observed a distinctive DA receptor subtype distribution, with evidence of the presence of mRNA encoding both subtypes of the D(1)-like DA receptor family (D(1) and D(5)), while the D(4) receptors were the only expressed subtype of the D(2)-like family. These results suggested that DAergic drugs used for the treatment of a number of diseases may influence the micturition physiology not only in the CNS, but at the peripheral level as well.

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.

Dopamine and angiotensin as renal counterregulatory systems controlling sodium balance

PURPOSE OF REVIEW

To review the recent evidence demonstrating how the renal dopaminergic and angiotensin systems control renal electrolyte balance through various receptor-mediated pathways with counterregulatory interactions.

RECENT FINDINGS

Stimulation of the renal rennin-angiotensin system results in increased sodium reabsorption, whereas the opposite is true for stimulation of the renal dopaminergic system. An underactive renal dopaminergic system has been associated with increased sodium reabsorption and hypertension. Recent findings indicate novel cell surface receptor-mediated mechanisms by which these two renal endocrine systems directly counterregulate each other. Each of the dopamine receptors (D1R through D5R) have been implicated in dopamine-mediated natriuresis, in addition to counterregulating the angiotensin type 1 R. Dopamine D1-like (D1R and D5R) stimulation has also been found to induce an AT2 receptor- dependent natriuresis. Recently, it has also been discovered that reactive oxygen species can play a role in inactivating the D1 receptor and activating the angiotensin type 1 R.

SUMMARY

Current therapeutic interventions for hypertension predominantly involve correction of an overactive rennin-angiotensin aldosterone system. Recent evidence suggests that stimulation of the renal dopaminergic system and possibly activation of AT2 receptors, as well as decreasing reactive oxygen species, may provide additional therapeutic approaches.

The inflammatory response in the MPTP model of Parkinson's disease is mediated by brain angiotensin: relevance to progression of the disease

The neurotoxin MPTP reproduces most of the biochemical and pathological hallmarks of Parkinson's disease. In addition to reactive oxygen species (ROS) generated as a consequence of mitochondrial complex I inhibition, microglial NADPH-derived ROS play major roles in the toxicity of MPTP. However, the exact mechanism regulating this microglial response remains to be clarified. The peptide angiotensin II (AII), via type 1 receptors (AT1), is one of the most important inflammation and oxidative stress inducers, and produces ROS by activation of the NADPH-oxidase complex. Brain possesses a local angiotensin system, which modulates striatal dopamine (DA) release. However, it is not known if AII plays a major role in microglia-derived oxidative stress and DA degeneration. The present study indicates that in primary mesencephalic cultures, DA degeneration induced by the neurotoxin MPTP/MPP(+) is amplified by AII and inhibited by AT1 receptor antagonists, and that protein kinase C, NADPH-complex activation and microglial activation are involved in this effect. In mice, AT1 receptor antagonists inhibited both DA degeneration and early microglial and NADPH activation. The brain angiotensin system may play a key role in the self-propelling mechanism of Parkinson's disease and constitutes an unexplored target for neuroprotection, as previously reported for vascular diseases.

Hypertension in mice lacking the CXCR3 chemokine receptor

The CXC chemokine receptor 3 (CXCR3) has been linked to autoimmune and inflammatory disease, allograft rejection, and ischemic nephropathy. CXCR3 is expressed on endothelial and smooth muscle cells. Although a recent study posited that antagonizing of CXCR3 function may reduce atherosclerosis, the role of CXCR3 in controlling physiological vascular functions remains unclear. This study demonstrates that disruption of CXCR3 leads to elevated mean arterial pressures in anesthetized and conscious mice, respectively. Stimulation of isolated resistance vessels with various vasoconstrictors showed increased contractibility in CXCR3-/- mice in response to angiotensin II (ANG II) and a decreased vasodilatation in response to acetylcholine (ACh). The increased contractibility was related to higher ANG II type 1 receptor (AT1R) expression, whereas the decreased vasodilatation was related to lower M3-ACh receptor expression in the mesenteric arteries of CXCR3-/- mice compared with wild-type mice. The vasodilatatory response to ACh could be antagonized by the nonselective ACh receptor antagonist atropine and the selective M3 receptor antagonist 4-DAMP, but not by M1, M2, and M4 receptor antagonists. Additionally, EMSA studies revealed that transcription factors SP-1 and EGR-1 interact as a complex with the murine AT1R promoter region. Furthermore, we could show increased expression of SP-1 in CXCR3-/- mice indicating an imbalanced SP-1 and EGR-1 complex formation which causes increased AT1R expression and hypertension. The data indicate that CXCR3 receptor is important in vascular contractility and hypertension, possibly through upregulated AT1R expression.