Exaggerated response to adenosine in kidneys from high salt-fed rats: role of epoxyeicosatrienoic acids

Abstract

450 (CYP)-dependent epoxyeicosatrienoic acids (EETs) dilate rat preglomerular microvessels when adenosine 2A receptors (A2AR) are stimulated. As high salt (HS) intake increases epoxygenase activity and adenosine levels, we hypothesized that renal adenosine responses would be greater in HS-fed rats. Male Sprague-Dawley rats were fed either HS (4.0% NaCl) or normal salt (NS; 0.4% NaCl) diet. On day 8, isolated kidneys were perfused with Krebs' buffer containing indomethacin (10 M) and L-NAME (200 M) and preconstricted to ϳ150 mmHg with infusion of phenylephrine (10 Ϫ7 M). Renal effluents were extracted for analysis of eicosanoids by gas chromatography-mass spectrometry. Bolus injections of the stable adenosine analog 2-chloroadenosine (2-CA; 0.1-10 g) resulted in dose-dependent dilation; at 10 g, perfusion pressure (PP) was lowered to a greater extent in the kidneys of HS rats compared with NS rats (Ϫ60 Ϯ 4 vs. Ϫ31 Ϯ 8 mmHg; P Ͻ 0.05) and the area of response was increased (27 Ϯ 6 vs. 9 Ϯ 4 mm 2 ; P Ͻ 0.05), as was EET release (132 Ϯ 23 vs. 38 Ϯ 18 ng; P Ͻ 0.05). HS treatment increased A2AR and CYP2C23 protein expression. A selective epoxygenase inhibitor, MS-PPOH (12 M), significantly reduced the response to 2-CA in HS rats; PP, area of response, and EET release decreased by 40, 70, and 81%, respectively, whereas lesser changes were evident in NS kidneys. Thus the greater vasodilator response to 2-CA seen in kidneys obtained from HS-fed rats was mediated by increased EET release. As EETs are renal vasodilator and natriuretic eicosanoids, interactions between adenosine and EETs may contribute to the adaptive response to HS intake. adenosine receptors; cytochrome P-450

Failure to upregulate the adenosine2Areceptor-epoxyeicosatrienoic acid pathway contributes to the development of hypertension in Dahl salt-sensitive rats

“…1A). Because 2-CA is a nonselective agonist of all four adenosine receptors, we determined whether 2-CA-induced vasodilation of isolated, perfused Dahl rat kidneys was mediated by stimulating A 2A Rs, thereby increasing EET synthesis, as we have reported for SD rats (23). To assess the involvement of A 2A R in 2-CA-induced vasodilation of isolated, perfused kidneys obtained from Dahl SR and SS rats, we determined responsiveness to 2-CA in the absence and presence of ZM 241385 (1 M), a selective A 2A R antagonist (Fig.…”

“…The adenosineepoxygenase pathway is upregulated by HS intake in normotensive SD rats (23). Because this pathway is antipressor, we examined the role of the adenosine-epoxygenase pathway in Dahl SS hypertensive rats, a genetic model of salt-sensitive hypertension.…”

“…The right kidney was prepared for perfusion as described previously (23). After laparotomy, the right renal artery was cannulated with a 21-gauge needle; the kidney was then removed and perfused with warmed (37°C), gassed (95% O2-5% CO2) Krebs-Henseleit buffer at a flow rate of 7 ml/min using a Harvard Apparatus peristaltic pump.…”

“…Adenosine-induced renovascular dilation in Sprague-Dawley (SD) rats is mediated via activation of A 2A R, which we have linked to stimulation of EET synthesis (7,23). In SD rats, HS intake augmented renovascular responses to a nonselective adenosine receptor agonist, 2-chloroadenosine (2-CA), associated with increased renal protein expression of the A 2A R and CYP2C23, a salt-inducible epoxygenase that promotes increased renal efflux of EETs and the hydrolysis products of EETs, dihydroxyeicosatrienoic acids (DHTs).…”

Purinergic signalling in the kidney in health and disease

“…Mice lacking P2Y 2 receptors have salt-resistant hypertension [309]. There is an exaggerated response to adenosine in kidneys from high salt-fed rats [223]. While the P2X7 receptor is only weakly expressed in healthy kidney glomerulus, it is significantly upregulated in ren-2 transgenic hypertension [393].…”