Inhibitors of 20-Hydroxyeicosatetraenoic Acid Reduce Renal Vasoconstrictor Responsiveness

Abstract

20-Hydroxyeicosatetraenoic acid (20-HETE) is a cytochrome P450-derived constrictor eicosanoid produced by the preglomerular vasculature where it contributes to regulation of tone. Removal of the tonic inhibitory influence of nitric oxide (NO) has been reported to increase renal 20-HETE release. Because inhibition of NO synthesis enhances responses to vasoconstrictor agents, we examined a contribution for increased 20-HETE generation. In the rat kidney perfused with Krebs' buffer, responses to U46619 (9,11-dideoxy-9␣,11␣-methanoepoxy PGF 2␣ ), a thromboxane A 2 mimetic, were compared before and after 50 M L-nitroarginine (L-NA) to inhibit NO synthase. L-NA raised perfusion pressure (PP) from 79 Ϯ 3 to 190 Ϯ 7 mm Hg and enhanced constrictor responsiveness to U46619. U46619 (10, 30, 100, and 300 ng) increased PP by 7 Ϯ 1, 17 Ϯ 2, 50 Ϯ 7, and 67 Ϯ 7 mm Hg, respectively, before L-NA and 15 Ϯ 1, 37 Ϯ 7, 68 Ϯ 10, and 85 Ϯ 11 mm Hg, respectively, after L-NA, which did not increase 20-HETE efflux from the kidney. Nonetheless, an inhibitor of -hydroxylase, dibromododecencyl methylsulfonimide (DDMS), which reduced 20-HETE release, normalized the enhanced responsiveness to U46619. When PP was elevated with phenylephrine, vasoconstrictor responses to U46619 were similarly enhanced, an effect that was also prevented by DDMS. DDMS and an antagonist of 20-HETE, 20-HEDE [20-hydroxyeicosa-6(Z),15(Z)-dienoic acid], also reduced vasoconstrictor responses to U46619 in the absence of elevation of PP. Because 20-HETE inhibits K ϩ channels, we examined the effects of K ϩ channel inhibitors on vasoconstrictor responses and showed that both tetraethylammonium (TEA) and charybdotoxin enhanced renal vasoconstrictor responses to U46619. However, the inhibitory effects of 20-HEDE on vasoconstrictor responses remained after treatment with TEA. These results support a role for 20-HETE vasoconstrictor responses but suggest an action independent of K ϩ channels.

Role of 20-hydroxyeicosatetraenoic acid (20-HETE) in vascular system

“…Endothelin-1 stimulates the formation of 20-HETE in isolated rat perfused kidney (Oyekan et al, 1997;Hercule and Oyekan, 2000;Imig et al, 2000). Quilley et al (2003) also showed that U46619, an analog of thromboxane A2 stimulated the production of 20-HETE and released 20-HETE partially act as a second messenger to cause vasoconstriction in rat perfused kidney.…”

20-HETE-mediated vasoconstriction by hemoglobin-O2carrier in Sprague-Dawley but not Wistar rats

“…Inhibition of NO synthase increased efflux of 20-HETE from both Wistar and SpragueDawley kidneys with peak levels of 3.6 ng/min from SpragueDawley rats and but only 1.4 from Wistar rats (17). However, subsequent investigations suggest that the rise in 20-HETE release during isolated perfusion may have been a time-dependent phenomenon unrelated to inhibition of NO synthase (18). Sprague-Dawley alveolar macrophages produce 10 times more NO than Wistar macrophages when stimulated by lipopolysacharide (9) and NO contributes to nonadrenergic noncholinergic relaxation significantly more in Sprague-Dawley intestine than in Wistar intestine (14,15).…”

A vibrator prevents streaming during close-arterial infusion into the kidney

“…The greatest effect of vibration on renal blood flow (55% reduction vs. 25% reduction) occurred after infusion of phenylephrine at 1.5 ϫ 10 Ϫ7 g (infused over 30 s, at a flow rate of ϳ5 ml/min). Significantly, this is the concentration of phenylephrine (7.5 ϫ 10 Ϫ7 M), which consistently induces vasoconstriction in the isolated, perfused kidney (17,19).…”