Increase in vasomotor tone upon IP receptor blockade in isolated murine renal arteries - role of lipoxygenase(s)

Abstract

BACKGROUND: Arachidonic acid is the source of vasoconstrictor prostanoids produced by cyclooxygenases and released as endotheliumderived contracting factors (EDCF) upon stimulation with acetylcholine. The renal vasculature contributes to the regulation of arterial blood pressure and is highly sensitive to vasoconstrictor agonists, in particular prostaglandins. The role of basally released endogenous prostacyclin in renal vasomotor control is unknown. Hence, the present experiments examined the effect of a prostacyclin receptor (IP) antagonist in quiescent isolated renal arteries. METHODS: Isometric tension was recorded in renal artery rings (with and without endothelium) from 7 to 15 weeks young male C57BL/6N wild-type mice using Halpern-Mulvany myographs. Quiescent preparations were incubated with indomethacin, meclofenamate (both 10-5 M), or nordihydroguaiaretic acid (NDGA) to inhibit cyclooxygenases or lipoxygenases, respectively, prior the addition of the IP receptor antagonist CAY10441 (10-6 M). All experiments were performed in the presence of an inhibitor of nitric oxide synthases (L-NAME, 3 X 10-4 M). RESULTS: CAY10441 caused increases in tension, which were endothelium-independent. Quinacrine (10-5 M) inhibited the contractions, indicating the involvement of phospholipase A2 leading to the release of arachidonic acid. The contractions to CAY10441 were not prevented by either indomethacin or meclofenamate (n = 4), ruling out a role of cyclooxygenase(s). They were largely reduced by 10-6 M and nearly abolished by 10-5 M NDGA (n = 5, P < 0.05). Cyclooxygenase-dependent contractions to acetylcholine (10-4 M) and bradykinin (10-6 M) were also abolished by NDGA (10-5 M). In addition, the lipoxygenase inhibitor slightly but significantly attenuated contractions to serotonin (10_5 M), but not those to endothelin-1 (10-8 M), phenylephrine (10-5 M), and U46619 (10-6 M). CONCLUSIONS: These results suggest that in renal arteries of the mouse IP receptors are essential in the regulation of basal vasomotor tone, since antagonizing them leads to vasoconstriction. Blockade of IP receptors unmasks the production of vasoconstrictors in vascular smooth muscle cells, which depends on the activity of phospholipase A2 but not that of cyclooxygenase(s). The present findings suggest a key role for lipoxygenases in the increases in basal tone induced by IP receptor blockade.