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© Copyright 2004 The British Pharmacological Society

071P GKT, University of London
Winter Meeting December 2003

cyclooxygenase products of 20-hydroxyeicosatetraenoic acid (HETE) increase spontaneous tone in aorta of deoxycorticosterone acetate (DOCA)-salt hypertensive rats
J. R. McNeill, X. Qiu, and M. Ghosh. Department of Pharmacology and CRFRU, Univ. of Saskatchewan, Canada.

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McNeill JR
Qiu X
Ghosh M

Spontaneous tone increases as a function of preload in aortic rings isolated from DOCA-salt hypertensive rats, but not from SHAM normotensive rats (Ghosh et al., 2003a). Recently, we reported that the cytochrome P450 (CYP) 4A product, 20-HETE, increased spontaneous tone in rings from DOCA-salt hypertensive rats (Ghosh et al., 2003b), but the role of cyclooxygenase (COX) products of 20-HETE had not been examined. The aim of this study was to investigate this issue by recording responses to 20-HETE in the presence (60 min) and absence of the COX inhibitor, valeroyl salicylate (VAS, 3 mM) or the BKca channel blocker, iberiotoxin (IBT, 10nM).

Under anaesthesia (isoflurane)*, the right kidney was removed in male Sprague-Dawley rats (300-400g). Silastic strips impregnated with 100 mg.kg-1 of DOCA were implanted s/c. After recovery, these rats were offered a 0.9% NaCl/0.2% KCl drinking solution. In the SHAM group, DOCA-free silastic strips were implanted and tap water was supplied for drinking. Three weeks later, blood pressure was higher (P < .05) in the DOCA-salt than in the SHAM group (158 ± 3 vs 100 ± 3 mmHg). Under anesthesia, the aorta was isolated. Aortic rings were mounted in an organ bath containing Kreb's buffer (37°C). The preload was increased to an optimal tension of 5 g in the presence of 100 nM sodium nitroprusside (SNP) to ensure passive conditions. Tension was recorded isometrically.

Endogenous 20-HETE levels were higher (P < .05) in aortae from DOCA-salt hypertensive (26 ± 2 ng/g tissue) than in those from SHAM normotensive rats (7 ± 5 ng/g).

Treatment
Endo + (n=4-6)
Endo - (n=4-6)
Untreated
37 ± 2
55 ± 4
20- HETE
54 ± 4*
62 ± 4
ABT
19 ± 4*
43 ± 2
VAS
2 ± 2*
27 ± 1*
VAS + 20-HETE
6 ± 3*ns
37 ± 3* ns
IBT
54 ± 3*
61 ± 3*
IBT + 20-HETE
54 ± 2*ns
58 ± 3*ns

*P < .05 compared to untreated. ns - not significantly different compared to VAS alone or IBT alone (ANOVA).

Washout of SNP evoked spontaneous tone in rings from DOCA-salt (Table 1) but not SHAM rats (data not shown). 20-HETE increased spontaneous tone in endothelium-intact but not endothelium-denuded rings. Aminobenzotriazole (ABT, 10 µM), a CYP4A inhibitor, reduced tone. VAS reduced and IBT increased tone. 20 HETE failed to increase spontaneous tone in the presence of either VAS or IBT.

We conclude that COX metabolites of 20-HETE mediate the increases in tone evoked by 20-HETE. These COX metabolites appear to exert their effect through BKca channels.

Ghosh, M. et al. (2003a) Br. J. Pharmacol. (in press).
Ghosh, M. et al. (2003b) FASEB Journal. 17(5): A1248.

*Protocols approved by the Animal Care Committee at the University of Saskatchewan.