5,6-Epoxyeicosatrienoic Acid Mediates the Enhanced Renal Vasodilator Response to Arachidonic Acid (AA) in the SHR.
The cytochrome P450-dependent renal vasodilator effect of arachidonic acid (AA) that is expressed when cyclooxygenase is inhibited and perfusion pressure (PP) is elevated, is enhanced in SHR. In kidneys perfused with Krebs’ solution and preconstricted with phenylephrine to increase PP to ca 200 mmHg, 5 μg of AA reduced PP by 92 ± 10 mmHg in SHR compared to 44.5 ± 5 mmHg for WKY rats. In contrast, the dilator effects of acetylcholine (Ach; 0.1 μg) or sodium nitroprusside (SNP; 1 μg) were not different. As the response to AA was inhibited by ETYA (4 μM), an inhibitor of all AA oxygenase pathways, and also inhibited by the selective epoxygenase inhibitors, miconazole (0.3 μM) and MSPPOH (12 μM), we concluded that the vasodilator mediator(s) of the AA response was most likely an epoxyeicosatrienoic acid (EET). We therefore, assessed the renal vascular responses to EETs in the SHR and WKY. We found that 5,6-EET, 8,9-EET, and 11,12-EET were dilators in both SHR and WKY, whereas 14,15-EET produced constriction. 5,6-EET was the most potent dilator of the EET regioisomers in the SHR resulting in a decrease in PP of 56 ± 5 mmHg compared to 12 ± 4 mmHg for 8,9-EET and 15 ± 4 mmHg for 11,12-EET. The decrease in PP elicited by 5 μg of 5,6-EET was greater in SHR, 56 ± 5 mmHg compared to 29 ± 4 mmHg for WKY rats whereas the responses to the other EET regioisomers did not differ. We measured the release of EETs from SHR and WKY kidneys in response to 5 μg of AA, by GC-MS in negative ionization mode using selective ion monitoring. The release of 5,6-EET was increased in SHR (from a basal level of 0.5 ± 0.04 to 0.9 ± 0.1 ng/min; P<0.05) compared to WKY (from a basal level of 0.6 ± 0.2 to 0.7 ± 0.2 ng/min), whereas the release of the other EETs were not different. We suggest that 5,6-EET is the most likely mediator of the AA response and that the augmented vasodilator response to AA in the SHR kidney might be linked to increased production of and responsiveness to 5,6-EET.