Background: Epoxyeicosatrienoic acids (EETs) are released from the endothelium and regulate vascular tone as an endothelium-derived hyperpolarising factor. EETs are synthesised from arachidonic acids by cytochrome P450 enzymes, and soluble epoxide hydrolase (SEH) inhibition may up-regulate EETs. EETs signaling may be implicated in cardiovascular risk groups. The effects of two agonists in stimulating EETs release were compared, and the best agonist was chosen to investigate this pathway in cardiovascular patient groups, and to confirm target engagement in a first in human clinical trial of a novel SEH inhibitor.

Methods: Healthy volunteers (12 male, 12 female) underwent 4 forearm venous occlusion plethysmography studies to compare the effects of intra-arterial bradykinin and acetylcholine co-infused with saline, fluconazole (cytochrome P450 inhibitor), L-monomethylarginine (nitric oxide synthase inhibitor) plus aspirin (cyclo-oxygenase inhibitor) (LNMMA+ASA), or with all three inhibitors (Triple). Data were analysed by repeated measures analysis of variance. Mean±SEM are presented.

Results: Fluconazole had no effect on basal tone (p=0.25). Bradykinin and acetylcholine both caused dose related vasodilatation (p<0.0001 vs. p<0.001). Fluconazole inhibited bradykinin-induced flow, but not acetylcholine (p<0.0001 vs. p=0.86). LNMMA+ASA inhibited bradykinin and acetylcholine induced vasodilatation (p<0.0001 vs. p<0.0001). There was no additive effect with triple inhibition. At top agonist doses, fluconazole inhibited bradykinin-induced flow, but not acetylcholine (−18.84±5.08% vs. 3.36±9.07%; p=0.01). LNMMA+ASA inhibited bradykinin and acetylcholine induced flow (−35.74±7.57% vs. −32.78±10.60% p=0.74). There were no gender differences.

Conclusions: Basal tone is not dependent on EETs signaling. Bradykinin-induced flow is EETs dependent, therefore bradykinin was chosen to probe EETs in cardiovascular patient groups.