OBJECTIVES - Epoxygenase metabolites produced by the kidney affect renal blood flow and tubular transport function and 11,12-epoxyeicosatrienoic acid (11,12-EET) has been putatively identified as an endothelium-derived hyperpolarizing factor. The current studies were performed to determine the influence of 11,12-EET on the regulation of afferent arteriolar diameter in angiotensin II-infused hypertensive rats.
MATERIALS AND METHODS - Male Sprague-Dawley rats received angiotensin II (60 ng/min) or vehicle via an osmotic minipump. Angiotensin II-infused hypertensive and vehicle-infused normotensive rats were studied for 2 weeks following implantation of the minipump. Renal microvascular responses to the sulfonimide analog of 11,12-EET (11,12-EET-SI) and angiotensin II were observed utilizing the in-vitro juxtamedullary nephron preparation. Renal cortical epoxygenase enzyme protein levels were quantified by Western blot analysis. Renal microvessels were also isolated and epoxygenase metabolite levels measured by negative ion chemical ionization (NICI)/gas chromatography-mass spectroscopy.
RESULTS - Systolic blood pressure averaged 118 +/- 2 mmHg prior to pump implantation and increased to 185 +/- 7 mmHg in rats infused with angiotensin II for 2 weeks. Afferent arteriolar diameters of 2-week normotensive animals averaged 22 +/- 1 microm. Diameters of the afferent arterioles were 17% smaller in hypertensive rats (P< 0.05); however, arterioles from both groups responded to 11,12-EET-SI (100 nmol) with similar 15-17% increases in diameter. As we previously demonstrated, the afferent arteriolar reactivity to angiotensin II was enhanced in angiotensin II-infused animals. Interestingly, elevation of 11,12-EET-SI levels to 100 nmol reversed the enhanced vascular reactivity to angiotensin II associated with angiotensin II hypertension. Renal microvascular EET levels were not different between groups and averaged 81 +/- 9 and 87 +/- 13 pg/mg per 30 min in normotensive and hypertensive animals, respectively. Renal cortical microsomal levels of the epoxygenase CYP2C23 and CYP2C11 proteins were also similar in normotensive and angiotensin II hypertensive rats.
CONCLUSIONS - Taken together, these data support the concept that renal microvascular 11,12-EET activity and levels may not properly offset the enhanced angiotensin II renal vasoconstriction during angiotensin II hypertension.