Altered Functioning of Both Renal Dopamine D1 and Angiotensin II Type 1 Receptors Causes Hypertension in Old Rats

Abstract

Activation of renal dopamine D1 (D1R) and angiotensin II type 1 receptors (AT 1 Rs) influences the activity of proximal tubular sodium transporter Na,K-ATPase and maintains sodium homeostasis and blood pressure. We reported recently that diminished D1R and exaggerated AT 1 R functions are associated with hypertension in old Fischer 344 × Brown Norway F1 (FBN) rats, and oxidative stress plays a central role in this phenomenon. Here we studied the mechanisms of age-associated increase in oxidative stress on diminished D1R and exaggerated AT 1 R functions in the renal proximal tubules of control and antioxidant Tempol-treated adult and old FBN rats. Although D1R numbers and D1R agonist SKF38393-mediated stimulation of [ 35 S]-GTPγS binding (index of D1R activation) were lower, G protein–coupled receptor kinase 4 (kinase that uncouples D1R) levels were higher in old FBN rats. Tempol treatment restored D1R numbers and G protein coupling and reduced G protein–coupled receptor kinase 4 levels in old FBN rats. Angiotensin II–mediated stimulation of [ 35 S]-GTPγS binding and Na,K-ATPase activity were higher in old FBN rats, which were also restored with Tempol treatment. We also measured renal AT 1 R function in adult and old Fischer 344 (F344) rats, which, despite exhibiting an age-related increase in oxidative stress and diminished renal D1R function, are normotensive. We found that diuretic and natriuretic responses to candesartan (indices of AT 1 R function) were similar in F344 rats, a likely explanation for the absence of age-associated hypertension in these rats. Perhaps, alterations in both D1R (diminished) and AT 1 R (exaggerated) functions are necessary for the development of age-associated hypertension, as seen in old FBN rats.

Altered signaling pathways linked to angiotensin II underpin the upregulation of renal Na+-ATPase in chronically undernourished rats

“…It is clear that undernutrition affects signaling pathways selectively. Thus, it is possible that undernutrition also affects the regulatory phosphorylations that have been demonstrated for (Na + + K + )ATPase [43,50,55], as well as those that depend of interactions on the dopaminergic system with RAS [56][57][58]. Besides the local renal RAS, it is also clear that undernutrition simultaneously alters the circulatory, cardiac and brain RAS, facing the increased catecholamine levels [1,59], accentuated hypertension [60] and structural and electric cardiac remodeling [5].…”

Renal dopamine and angiotensin II receptor signaling in age-related hypertension

“…Readers are directed to a recent review elegantly compiled by Zeng and Jose (100) for greater detail of the role of each receptor subtype in blood pressure regulation. Below, we summarize the current knowledge regarding the D1-like receptor, as this is perhaps the only dopamine receptor studied in the aging kidney in the context of blood pressure (6,7,25,26,35).…”

Human kidney-2 cells harbor functional dopamine D1 receptors that require Giαfor Gq/11αsignaling

“…35 S-GTP␥S (0.6 nM, ϳ100,000 cpm, Perkin Elmer, Waltham, MA) binding in the absence and presence of FD and ANG II was performed in the cellular membranes by our published method (10). Briefly, assays were performed in 96-well multiscreen filter plates (EMD Millipore, Billerica, MA) containing 5 g of membrane protein and 35 S-GTP␥S in an assay buffer (100 l final volume, 25 mM HEPES, 15 mM MgCl 2, 100 mM NaCl, 1 mM EDTA, 1 mM DTT, and 1 M GDP).…”

“…Western blotting. Western blotting was performed as previously published (10). Cell homogenates, cytosol, and membrane preparations (30 g) were resolved by SDS-PAGE on 8 -16% Trisglycine gels (Thermo Scientific) in HEPES buffer, blotted onto PVDF membrane for 3 h at 4°C, and membranes were probed with respective antibodies in 5% BSA in TBST overnight at 4°C.…”