Role of epoxyeicosatrienoic acids in renal functional response to inhibition of NO production in the rat

Cytochrome P450 epoxygenases, soluble epoxide hydrolase, and the regulation of cardiovascular inflammation

The cytochrome P450 (CYP) epoxygenase enzymes CYP2J and CYP2C catalyze the epoxidation of arachidonic acid to epoxyeicosatrienoic acids (EETs), which are rapidly hydrolyzed to dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolase (sEH). It is well-established that CYP epoxygenase-derived EETs possess potent vasodilatory effects; however, the cellular effects of EETs and their regulation of various inflammatory processes have become increasingly appreciated in recent years, suggesting that the role of this pathway in the cardiovascular system extends beyond the maintenance of vascular tone. In particular, CYP epoxygenase-derived EETs inhibit endothelial activation and leukocyte adhesion via attenuation of nuclear factor-kappaB activation, inhibit hemostasis, protect against myocardial ischemia-reperfusion injury, and promote endothelial cell survival via modulation of multiple cell signaling pathways. Thus, the CYP epoxygenase pathway is an emerging target for pharmacological manipulation to enhance the cardiovascular protective effects of EETs. This review will focus on the role of the CYP epoxygenase pathway in the regulation of cardiovascular inflammation and (1) describe the functional impact of CYP epoxygenase-derived EET biosynthesis and sEH-mediated EET hydrolysis on key inflammatory process in the cardiovascular system, (2) discuss the potential relevance of this pathway to pathogenesis and treatment of cardiovascular disease, and (3) identify areas for future research.

Effects of ATP on rat renal haemodynamics and excretion: role of sodium intake, nitric oxide and cytochrome P450

AIM

Adenosine-5'-triphosphate (ATP) affects intrarenal vascular tone and tubular transport via P2 receptors; however, the actual role of the system in regulation of renal perfusion and excretion remains unclear and is the subject of this whole-kidney study.

METHODS

Effects of suprarenal aortic ATP infusion, 0.6-1.2 mg kg(-1) h(-1), were examined in anaesthetised rats maintained on low- (LS) or high-sodium (HS) diet. Renal artery blood flow (RBF, transonic flow probe) and the perfusion (laser-Doppler flux) of the superficial cortex (CBF) and outer and inner medulla (OM-BF, IM-BF) were measured, together with sodium and water excretion and urine osmolality.

RESULTS

Adenosine-5'-triphosphate did not change arterial pressure, RBF or CBF while the effects on medullary perfusion depended on sodium intake. In LS rats ATP increased IM-BF 19 +/- 6%, the effect was prevented by inhibition of nitric oxide (NO) with N-nitro-l-arginine methyl ester. In HS rats ATP decreased OM-BF 16 +/- 3% and IM-BF (7 +/- 4%, not significant); previous inhibition of cytochrome P450 with 1-aminobenzotriazol blunted the OM-BF decrease and reversed the previous decrease of IM-BF to a 13 +/- 8% increase. Inhibition of P2 receptors with pyridoxal derivative (PPADS) abolished medullary vascular responses to ATP. In HS rats pre-treated with PPADS, ATP increased tubular reabsorption, probably via adenosine formation and stimulation of P1 receptors.

CONCLUSION

The data indicate a potential role of ATP in the selective control of renal medullary perfusion, different in sodium depleted and sodium replete rats. The action of ATP appears to be mediated by the NO system and the cytochrome P450 dependent vasoactive metabolites.