Formation and actions of 20-hydroxyeicosatetraenoic acid in rat renal arterioles

The present study examined whether preglomerular arterioles of the rat produce 20-hydroxyeicosatetraenoic acid (20-HETE) and whether 20-HETE is vasoactive on these vessels. Rat preglomerular arterioles produced 20-HETE (4.8 ± 1.0 pmol · min^-1 · mg^-1, n = 7) and, to a lesser extent, 14-, 15-, 11-, and 12-dihydroxyeicosatetraenoic acid, 6-ketoprostaglandin F(1α), and prostaglandin E₂ when incubated with [¹⁴C] arachidonic acid. The results of immunoblotting and reverse-transcription polymerase chain reaction experiments indicate that these vessels express mRNA and protein for a P-450 4A₂ enzyme. With the use of a rat juxtamedullary nephron microvascular preparation perfused in vitro with a cell-free media, addition of 20-HETE (1 nM-1 μM) to the bath reduced the diameter of proximal and distal portions of the afferent arterioles. At a concentration of 1 μM, the diameter of the proximal and distal portions of the afferent arteriole fell by 14 ± 1 and 16 ± 3% after 20-HETE. The response to 20-HETE (1 μM) was not altered by blockade of cyclooxygenase, lipoxygenase, and P-450 pathways. Blockade of the large-conductance Ca²⁺-activated K⁺ channel with tetraethylammonium (1 mM) reduced the diameter of afferent arterioles by 10% and blocked the vasoconstrictor response to 20-HETE (1 μM). These results indicate that 20- HETE is an endogenous constrictor of preglomerular arterioles and suggest a role for the P-450 4A₂ enzyme in the regulation of renal vascular tone.