Role of dopamine2-receptors in mediating renal vascular response to low dose dopamine infusion in the rat

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.

Comparison of Postoperative Acute Kidney Injury Between Laparoscopic and Laparotomy Procedures in Elderly Patients Undergoing Colorectal Surgery

OBJECTIVES

Postoperative acute kidney injury (AKI) has an unfavorable impact on both short-term and long-term outcomes. The aim of this retrospective study was to compare the incidence of postoperative AKI between laparoscopic and laparotomy procedures in elderly patients undergoing colorectal surgery.

METHODS

Medical records of elderly (65 y and older) patients who underwent colorectal cancer surgery between May 2016 and July 2018 at our tertiary hospital were reviewed. Patients with Union Internationale Contre le Cancer (UICC) stage II and III colorectal cancer, without neoadjuvant treatment, were divided into laparoscopic procedure group and laparotomy group. AKI, determined by the Acute Kidney Injury Network criteria, was compared between the 2 groups, before and after propensity matching. Multivariable analysis was made to identify independent risk factors of AKI.

RESULTS

In all, 285 patients met the study inclusion criteria. Postoperative AKI occurred only in 16 patients from the laparotomy group (n=212). The incidence of AKI was significantly lower in the laparoscopic procedure group (n=73) compared with the laparotomy group (0% vs. 7.5%; P=0.015). Seventy-three patients who underwent laparoscopic surgery were matched with 73 of 212 patients who underwent open surgery, by using propensity score analysis, and the incidence of AKI in the 2 groups was similar (0% vs. 8.3%; P=0.028). Multivariable analysis showed that intraoperative metaraminol dose >1 mg (odds ratio=2.742, P=0.042) is an independent risk factor for postoperative AKI.

CONCLUSION

In elderly patients, the incidence of AKI after colorectal cancer surgery is lower in the laparoscopic procedure group, maybe related to hemodynamic stability and less vasoconstriction.

Dose-dependent hemodynamic and metabolic effects of vasoactive medications in normotensive, anesthetized neonatal piglets

The developmentally regulated hemodynamic effects of vasoactive medications have not been well characterized. We used traditional and near-infrared spectroscopy monitoring technologies and investigated the changes in heart rate, blood pressure, common carotid artery (CCA) blood flow (BF), cerebral, renal, intestinal, and muscle regional tissue O2 saturation, and acid-base and electrolyte status in response to escalating doses of vasoactive medications in normotensive anesthetized neonatal piglets. We used regional tissue O2 saturation and CCA BF as surrogates of organ and systemic BF, respectively, and controlled minute ventilation and oxygenation. Low to medium doses of dopamine, epinephrine, dobutamine, and norepinephrine increased blood pressure and systemic and regional BF in a drug-specific manner, whereas milrinone exerted minimal effects. At higher doses, dopamine, epinephrine, and norepinephrine but not dobutamine decreased systemic, renal, intestinal, and muscle BF, while cerebral BF remained unchanged. Epinephrine induced significant increases in muscle BF and serum glucose and lactate concentrations. The findings reveal novel drug- and dose-specific differences in the hemodynamic response to escalating doses of vasoactive medications in the neonatal cardiovascular system and provide information for future clinical studies investigating the use of vasoactive medications for the treatment of neonatal cardiovascular compromise.

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.

Renal dopamine receptors in health and hypertension

During the past decade, it has become evident that dopamine plays an important role in the regulation of renal function and blood pressure. Dopamine exerts its actions via a class of cell-surface receptors coupled to G-proteins that belong to the rhodopsin family. Dopamine receptors have been classified into two families based on pharmacologic and molecular cloning studies. In mammals, two D1-like receptors that have been cloned, the D1 and D5 receptors (known as D1A and D1B, respectively, in rodents), are linked to stimulation of adenylyl cyclase. Three D2-like receptors that have been cloned (D2, D3, and D4) are linked to inhibition of adenylyl cyclase and Ca2+ channels and stimulation of K+ channels. All the mammalian dopamine receptors, initially cloned from the brain, have been found to be expressed outside the central nervous system, in such sites as the adrenal gland, blood vessels, carotid body, intestines, heart, parathyroid gland, and the kidney and urinary tract. Dopamine receptor subtypes are differentially expressed along the nephron, where they regulate renal hemodynamics and electrolyte and water transport, as well as renin secretion. The ability of renal proximal tubules to produce dopamine and the presence of receptors in these tubules suggest that dopamine can act in an autocrine or paracrine fashion; this action becomes most evident during extracellular fluid volume expansion. This renal autocrine/paracrine function is lost in essential hypertension and in some animal models of genetic hypertension; disruption of the D1 or D3 receptor produces hypertension in mice. In humans with essential hypertension, renal dopamine production in response to sodium loading is often impaired and may contribute to the hypertension. The molecular basis for the dopaminergic dysfunction in hypertension is not known, but may involve an abnormal post-translational modification of the dopamine receptor.

Attenuation of adenylate cyclase-induced increases in renal sodium excretion by the dopamine D-2 receptor agonist SK&F 89124

1. Although the existence of D-2 receptor binding sites in kidney has been identified, their functional significance in terms of influencing renal sodium excretion is not clear. In the present study we have examined the renal effects of a selective D-2 receptor agonist, SK&F 89124, in anaesthetized rats. 2. Intravenous infusion of SK&F 89124 (0.3, 1 and 3 micrograms kg-1 min-1 respectively) produced dose-dependent decreases in mean arterial blood pressure, heart rate and renal blood flow without causing any significant changes in urine output, urinary sodium excretion, renal vascular resistance or glomerular filtration rate. The changes in blood pressure, heart rate and renal blood flow caused by SK&F 89124 were abolished by a selective D-2 receptor antagonist, domperidone (50 micrograms kg-1 i.v. bolus; 10 micrograms kg-1 min-1). 3; Treatment with 3-isobutyl-1-methylxanthine (IBMX, 1 mg kg-1 bolus i.v.) or forskolin (200 micrograms kg-1 bolus i.v.) produced increases in heart rate, urine output and urinary sodium excretion, but there was no change in mean blood pressure. The natriuretic and diuretic response, but not tachycardiac response to IBMX or forskolin, was attenuated by SK&F 89124 (0.3 micrograms kg-1 min-1). 4. These results suggest that the selective D-2 receptor agonist, SK&F 89124, produced a significant decrease in blood pressure and heart rate via prejunctional D-2 receptor-mediated inhibition of noradrenaline release from postganglionic sympathetic nerve terminals. Although activation of renal tubular D-2 receptors had no significant effect on renal excretory function under basal conditions, it is likely that these receptors may exert an opposing effect on cAMP-mediated increases in renal sodium and water excretion.

Role of dopamine1-receptors in mediating renal responses to furosemide in the rat

1. Dopamine (DA) infusion enhanced the diuresis, natriuresis and kaliuresis evoked by furosemide, but this increase was significantly lower in the presence of SCH 23390, a selective DA1-dopaminergic antagonist. 2. Water, Na+ and K+ excretion induced by furosemide were reduced by haloperidol, and SCH 23390, whereas they were not affected by +/- sulpiride, a preferentially DA2-dopaminergic antagonist. 3. The treatments used did not modify the mean blood pressure during the experiments. 4. Our data show that renal responses to furosemide are attenuated by the DA1-dopaminergic antagonist. It is possible that endogenous DA, stimulating DA1 receptors in the rat kidney may be an important factor involved in the Na+, K+ and water excretion evoked by furosemide.

The role of dopamine in the control of corticosteroid secretion and metabolism

The relation between aldosterone and its trophins is altered by electrolyte status and in some hypertensive conditions in man by a mechanism or mechanisms not understood. Dopamine has been suggested as the agent for the altered sensitivity of plasma aldosterone to angiotensin II based on the results of studies with dopamine itself, both in vivo and in vitro, and with pharmacological agonists and antagonists. The evidence derived from these studies is presented and discussed. Questionable specificity of the agents used makes interpretation difficult. Similarly, dopamine infusion rates used in man and animals have resulted in plasma concentrations far in excess of those found normally and these pharmacological concentrations have been shown to alter both the clearance rate of exogenous angiotensin II, and the pattern of steroid response to ACTH. Direct study of adrenal tissue has provided more promising results. The adrenal cortex possesses specific dopamine receptors and dopamine has been shown to modify aldosterone biosynthesis in vitro. Moreover, dopamine is present in adrenocortical tissue in concentrations in the range calculated to operate the receptors. However, there is, as yet, no evidence that dopamine concentrations change in a physiological meaningful way, for example, during changes in sodium status.