Epoxyeicosatrienoic acids mediate adenosine-induced vasodilation in rat preglomerular microvessels (PGMV) via A2A receptors

I Activation of rat adenosine(2A) receptors (A(2A) R) dilates preglomerular microvessels (PGMV), an effect mediated by epoxyeicosatrienoic acids (EETs). 2 Incubation of PGMV with a selective A(2A) R agonist, 2-p-(2-carboxyethyl) phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680; 100 muM), increased isolated PGMV EET levels to 7.57+/-1.53 ng mg(-1) protein from 1.06+/-0.22 ng mg(-1) protein in controls (P<0.05), without affecting hydroxyeicosatetraenoic acid (HETE) levels (10.8 +/- 0.69 vs 11.02 +/- 0.74 ng mg(-1) protein). 3 CGS 21680-stimulated EETs was abolished by preincubation with an A(2A) R antagonist, 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM241385) (100 mu M). A selective epoxygenase inhibitor, methylsulfonyl-propargyloxyphenylhexanamide (MS-PPOH; 12 mu M) prevented CGS 21680-induced increase in EETs, indicating inhibition of de novo synthesis of EETs. 4 In pressurized (80 mmHg) renal arcuate arteries (110-130 mu m) preconstricted with phenylephrine (20 nM), superfusion with CGS 21680 (0.01-10 mu M) increased the internal diameter (i.d.) concentration-dependently; vasodilation was independent of nitric oxide and cyclooxygenase activity. CGS 21680 (10 mu M) increased i.d. by 32 +/- 61 mu m; vasodilation was prevented by inhibition of EET synthesis with MS-PPOH. 5 Addition of 3 nM 5,6-EET, 8,9-EET and 11,12-EET increased i.d. by 53 +/- 9, 17 +/- 4 and 53 +/- 5 mu m, respectively, whereas 14,15-EET was inactive. The responses to 5,6-EET were, however, significantly inhibited by indomethacin. 6 We conclude that 11,12-EET is the likely mediator of A(2A) R-induced dilation of rat PGMV. Activation of A(2A) R coupled to de novo EET stimulation may represent an important mechanism in regulating preglomerular microvascular tone.