Modulation by salt intake of the vascular response mediated through adenosine A_2A receptor: Role of CYP epoxygenase and soluble epoxide hydrolase

High-salt intake can change the effect of adenosine on arterial tone in mice. The aim of this study was to clarify the mechanism by which this occurs. Using aortas from mice fed a 4% NaCl (HS) or 0.45% NaCl (NS) diet for 4-5 wks, concentration-response curves for ACh, 5′-N-ethylcarboxamidoadenosine (NECA; adenosine analog) and 2-p-(2-carboxyethyl)phenethylamino-5′-N- ethylcarboxamidoadenosine hydrochloride hydrate [CGS-21680; A_2A adenosine receptor (A_2A AR) agonist] were obtained with N ^ω-nitro-L-arginine methyl ester (L-NAME; nitric oxide inhibitor, 10^-4 M), methylsulfonyl-propargyloxyphenylhexanamide [MS-PPOH; a CYP (cytochrome P-450) epoxygenase blocker, 10 ^-5 M including CYP2J2], 12-(3-adamantan-1-yl-ureido)dodecanoic acid [AUDA; soluble epoxide hydrolase (sEH) blocker, 10^-5 M], dibromo- dodecenylmethylsulfimide [DDMS; CYP ω-hydroxylase (CYP4A blocker), 10 ^-5 M], glibenclamide (K_ATP channel blocker; 10 ^-5 M) and 5-hydroxydecanoate (5-HD; mitochondrial-K_ATP channel blocker, 10^-4 M). HS dose response to ACh (10^-7 - 10^-5 M) was not different from NS (P > 0.05). Relaxation to 10^-6 M NECA was greater in the HS group (28.4 ± 3.9%) than in the NS group (4.1 ± 2.3%). Relaxation to 10^-6 M CGS-21680 was also greater in HS (27.9 ±4.5%) than in NS (4.9 ± 2.2%). L-NAME was able to block the dose response of ACh (10^-7 - 10^-5 M) equally in both HS and NS (P > 0.05), whereas L-NAME did not block CGS-21680-induced response in HS. In HS the CGS-21680 response was greatly reduced by MS-PPOH (to 4.7 ± 2.0%) and 5-HD (to 8.9 ± 2.2%), and also abolished by glibenclamide (-1.0 ± 5.9%). In NS, the CGS-21680 response was increased by AUDA (to 26.3 ± 3.4%) and DDMS (to 27.2 ± 3.0%). Compared with NS, HS vessels showed increased CYP2J2 and A _2A AR expression (46 and 74% higher, respectively) but decreased sEH, CYP4A, and A₁ AR expression (75, 30, and 55% lower, respectively). These data suggest that in mice fed NScontaining diet, upregulation of arterial A₁ receptor causes vasoconstriction via increased sEH and CYP4A proteins. However, in mice fed HS-containing diet, upregulation of A _2A receptor protein triggers vascular relaxation through ATP-sensitive (K⁺) channels via upregulation of CYP2J2 enzyme.