| 20-HETE; a patent vasoconstrictor and mediator of the myogenic response, is a major arachidonic acid metabolite in the rat renal preglomerular arteries. It is formed primarily by the cytochrome P450 (CYP) 4A isoforms. The CYP4A enzymes are highly homologous and share a common catalytic activity (o-hydroxylation and epoxidation), yet they show a distinct pattern of localization in the kidney, display distinct catalytic properties, and are subject different in regulatory mechanisms.;We measured 20-HETE synthesis and evaluated relationships between vessel diameter, 20-HETE production, and CYP4A isoform expression in microdissected segmental, interlobar, arcuate, and interlobular arteries as well as in the renal artery and the abdominal aorta. 20-HETE production in these vessels was segmented, with the highest levels produced in the small diameter interlobular arteries. 20-HETE synthesis decreased with increasing vessel diameter and was undetectable in the renal artery and the abdominal aorta. Western blot analysis indicated that the levels of CYP4A2/4A3 immunoreactive protein increased with decreased arterial diameter while those of CYP4A1-immunoreactive protein remained unchanged. Studies using PPOH, an inhibitor of CYP4A2/4A3 activity, and DDMS, an inhibitor of all CYP4A activity, suggest that 20-HETE synthesis in the arcuate and interlobular arteries is driven by both CYP4A1 and CYP4A2/4A3 while in the interlobar arteries, 20-HETE production is driven mainly by CYP4A1. Our real time PCR studies indicated that CYP4A2 is the major isoform expressed in the preglomerular arteries. CYP4A1 mRNA expression decreased with decreasing vessel diameter, while CYP4A2 and CYP4A8 mRNA expression increased as vessel diameter decreased. The finding that CYP4A8 mRNA expression in the preglomerular arteries corresponds with 20-HETE synthesis has prompted future studies on this isoform since it was thought that this enzyme is unimportant due to the lack of o-hydroxylase activity of the recombinant protein.;Studies using L-NAME, an inhibitor of nitric oxide synthase activity, suggest that this enzyme and its product nitric oxide, may; impact on the amount of 20-HETE produced. In vivo administration of L-NAME caused a significant increase in 20-HETE production in the segmental, interlobar, and arcuate arteries; 20-HETE production was unchanged in the interlobular artery.;20-HETE's role in controlling renal vascular tone is implicated by its localization in the renal microcirculation. The increase in CYP4A isoform expression and 20-HETE synthesis with decreasing diameter in the preglomerular arteries, along with 20-HETE's potent biological activity underscore the significance of 20-HETE as a modulator of renal hemodynamics. Manipulation of its synthesis in an isoform-specific manner may be important for the regulation of vascular tone. |
