The Relationship between the Intrarenal Dopamine System and Intrarenal Renin-angiotensin System Depending on the Renal Function

The renin-angiotensin-aldosterone system in kidney diseases of cats and dogs

The renin-angiotensin-aldosterone system (RAAS) has a well-established key pathophysiologic role in kidney diseases, and pharmacotherapy targeting this system is a mainstay of treatment of affected human beings, cats, and dogs. Several studies have evaluated the circulating RAAS in animals with spontaneous or experimentally induced kidney diseases. Evidence supporting the activation of this system has been demonstrated in some - but not all - studies and individuals, and the interindividual variability in circulating RAAS markers is high. Advances over the last few decades have expanded our understanding of the system, which now includes the existence of a counterbalancing "alternative" RAAS and tissular renin-angiotensin systems (RASs), the latter regulated independently of the circulating endocrine RAAS. The local RAS in the kidney, termed the intrarenal RAS, is currently recognized as an important regulator of kidney function and mediator of kidney disease. In general, information on the intrarenal RAS is lacking in cats and dogs with kidney diseases; however, existing limited data suggest its activation. Despite the inconsistent evidence for circulating RAAS activation in chronic kidney diseases, RAAS inhibitors have proven effective for the treatment of its common comorbidities, systemic arterial hypertension and renal proteinuria, in both cats and dogs. Further research of the circulating RAAS, the intrarenal RAS, and the interplay between these systems in the context of kidney diseases in companion animals might contribute to the development or refinement of future treatment strategies.

Dopamine in the Regulation of Glucose Homeostasis, Pathogenesis of Type 2 Diabetes, and Chronic Conditions of Impaired Dopamine Activity/Metabolism: Implication for Pathophysiological and Therapeutic Purposes

Dopamine regulates several functions, such as voluntary movements, spatial memory, motivation, sleep, arousal, feeding, immune function, maternal behaviors, and lactation. Less clear is the role of dopamine in the pathophysiology of type 2 diabetes mellitus (T2D) and chronic complications and conditions frequently associated with it. This review summarizes recent evidence on the role of dopamine in regulating insular metabolism and activity, the pathophysiology of traditional chronic complications associated with T2D, the pathophysiological interconnection between T2D and chronic neurological and psychiatric disorders characterized by impaired dopamine activity/metabolism, and therapeutic implications. Reinforcing dopamine signaling is therapeutic in T2D, especially in patients with dopamine-related disorders, such as Parkinson's and Huntington's diseases, addictions, and attention-deficit/hyperactivity disorder. On the other hand, although specific trials are probably needed, certain medications approved for T2D (e.g., metformin, pioglitazone, incretin-based therapy, and gliflozins) may have a therapeutic role in such dopamine-related disorders due to anti-inflammatory and anti-oxidative effects, improvement in insulin signaling, neuroinflammation, mitochondrial dysfunction, autophagy, and apoptosis, restoration of striatal dopamine synthesis, and modulation of dopamine signaling associated with reward and hedonic eating. Last, targeting dopamine metabolism could have the potential for diagnostic and therapeutic purposes in chronic diabetes-related complications, such as diabetic retinopathy.

Involvement of dopaminergic signaling in the cross talk between the renin-angiotensin system and inflammation

The renin-angiotensin system (RAS) is a fundamental regulator of blood pressure and has emerged as an important player in the control of inflammatory processes. Accordingly, imbalance on RAS components either systemically or locally might trigger the development of inflammatory disorders by affecting immune cells. At the same time, alterations in the dopaminergic system have been consistently involved in the physiopathology of inflammatory disorders. Accordingly, the interaction between the RAS and the dopaminergic system has been studied in the context of inflammation of the central nervous system (CNS), kidney, and intestine, where they exert antagonistic actions in the regulation of the immune system. In this review, we summarized, integrated, and discussed the cross talk of the dopaminergic system and the RAS in the regulation of inflammatory pathologies, including neurodegenerative disorders, such as Parkinson’s disease. We analyzed the molecular mechanisms underlying the interaction between both systems in the CNS and in systemic pathologies. Moreover, we also analyzed the impact of the commensal microbiota in the regulation of RAS and dopaminergic system and how it is involved in inflammatory disorders. Furthermore, we summarized the therapeutic approaches that have yielded positive results in preclinical or clinical studies regarding the use of drugs targeting the RAS and dopaminergic system for the treatment of inflammatory conditions. Further understanding of the molecular and cellular regulation of the RAS-dopaminergic cross talk should allow the formulation of new therapies consisting of novel drugs and/or repurposing already existing drugs, alone or in combination, for the treatment of inflammatory disorders.

The Urinary Angiotensinogen to Urinary Albumin Ratio Reflects Whether the Renin-angiotensin System in the Kidney Is Activated due to Filtration of Plasma Angiotensinogen through the Damaged Glomeruli or the Production of Angiotensinogen in the Proximal Tubules

Objective Urinary angiotensinogen (AGT) is a surrogate marker for intrarenal renin-angiotensin system (RAS) activity that plays an important role in the development of renal damage. Urinary AGT levels are determined by the filtration of plasma AGT through the damaged glomeruli and production of AGT in the proximal tubules. However, the relative merits of the filtration and production of urinary AGT levels in chronic kidney diseases (CKD) have not been clarified. Therefore, we investigated them in CKD patients. Methods We recruited 41 biopsy-proven patients diagnosed with IgA nephropathy (IgAN) in 31, membranous nephropathy (MN) in 5, and tubulointerstitial nephritis (TIN) in 5. The patients taking RAS blockers were excluded. Results The urinary albumin levels in MN patients were significantly higher and those in TIN patients significantly lower than in IgAN patients, and the urinary AGT levels in the MN and TIN patients were significantly higher than those in IgAN patients. Conversely, the urinary AGT-to-urinary albumin (urinary AGT/Alb) ratios were the same for IgAN and MN patients, and those of TIN patients were significantly higher than those of IgAN and MN patients. A multiple linear regression analysis revealed that the urinary AGT/Alb ratios had a significant positive association with IgAN and TIN after adjustments (β=0.75, and p<0.01). Conclusion These data suggest that the origins of urinary AGT may differ according to the etiology of renal damage [i.e. glomerular damage (such as IgAN and MN) or tubulointerstitial damage (such as TIN)], and a higher urinary AGT/Alb ratio, as in TIN, may reflect AGT production in the kidney.

Kidney dopamine D1-like receptors and angiotensin 1-7 interaction inhibits renal Na+ transporters

The role of dopamine D₁-like receptors (DR) in the regulation of renal Na⁺ transporters, natriuresis, and blood pressure is well established. However, the involvement of the angiotensin 1-7 (ANG 1-7)-Mas receptor in the regulation of Na⁺ balance and blood pressure is not clear. The present study aimed to investigate the hypothesis that ANG 1-7 can regulate Na⁺ homeostasis by modulating the renal dopamine system. Sprague-Dawley rats were infused with saline alone (vehicle) or saline with ANG 1-7, ANG 1-7 antagonist A-779, DR agonist SKF38393, and antagonist SCH23390. Infusion of ANG 1-7 caused significant natriuresis and diuresis compared with saline alone. Both natriuresis and diuresis were blocked by A-779 and SCH23390. SKF38393 caused a significant, SCH23390-sensitive natriuresis and diuresis, and A-779 had no effect on the SKF38393 response. Concomitant infusion of ANG 1-7 and SKF38393 did not show a cumulative effect compared with either agonist alone. Treatment of renal proximal tubules with ANG 1-7 or SKF38393 caused a significant decrease in Na⁺-K⁺-ATPase and Na⁺/H⁺ exchanger isoform 3 activity. While SCH23390 blocked both ANG 1-7- and SKF38393-induced inhibition, the DR response was not sensitive to A-779. Additionally, ANG 1-7 activated PKG, enhanced tyrosine hydroxylase activity via Ser⁴⁰ phosphorylation, and increased renal dopamine production. These data suggest that ANG 1-7, via PKG, enhances tyrosine hydroxylase activity, which increases renal dopamine production and activation of DR and subsequent natriuresis. This study provides evidence for a unidirectional functional interaction between two G protein-coupled receptors to regulate renal Na⁺ transporters and induce natriuresis.