Red blood cells: reservoirs of cis- and trans-epoxyeicosatrienoic acids.

Epoxyeicosatrienoic acids (EETs) are candidate endothelium-derived hyperpolarizing factors that demonstrate a wide range of biological effects. The presence of both cis- and trans-EETs in rat plasma was identified with HPLC-electrospray ionization tandem mass spectrometry in this study. The total EETs in plasma are 38.2ng/ml with cis-EETs representing 21.4±0.4ng/ml and trans-EETs 16.8±0.4ng/ml. EETs in RBCs were estimated to be 20.2ng/109 RBCs, which corresponds to 200ng in RBCs contained in 1ml blood. RBC incubation with 10mM tert-butyl hydroperoxide resulted in 4.4-fold increase of total cis-EETs (from 9.2 to 40.2ng/109 RBCs) and 5.5-fold increase of total trans-EETs (from 11.0 to 60.8ng/109 RBCs). EETs were released (2ng/ml) from RBCs after incubation at 37°C for 10min even after being washed 3 times, indicating that RBCs are reservoirs of plasma EETs. The identification of cis- and trans-EETs in RBCs and in plasma as well as their release from RBCs suggest a vasoregulatory role of RBCs in view of their potent vasoactivity.