Role of cyclooxygenase-1-mediated prostacyclin synthesis in endothelium-dependent vasoconstrictor activity of porcine interlobular renal arteries

Abstract

This study aimed to determine whether PGI(2) would be evoked by the endogenous endothelial B(2) receptor agonist bradykinin (BK) in the porcine interlobular renal artery and, if so, to determine how it would influence the vasomotor reaction, and the specific cyclooxygenase (COX) isoform(s) involved in its synthesis. The production of the PGI(2) metabolite 6-keto-PGF(1α) was analyzed with HPLC-mass spectroscopy, while vasomotor reaction to PGI(2) or BK was determined with isometric force measurement. Results showed that BK evoked an increase in the production of 6-keto-PGF(1α), which was abolished by endothelial denudation that removed COX-1 expression, or was reduced by COX-1 inhibition. Interestingly, PGI(2) evoked a potent contraction, which was prevented by antagonizing thromboxane-prostanoid (TP) receptors and was not enhanced by antagonizing the vasodilator PGI(2) (IP) receptors. The IP receptor agonists MRE-269 and iloprost did not induce any relaxation. Moreover, iloprost, which is also a PGI(2) analog, caused a contraction, which was sensitive to TP receptor antagonism, but was to a significantly lesser extent than that of PGI(2). Indeed, IP receptors were not detected by RT-PCR or Western blotting in the vessel. Following nitric oxide synthase (NOS) inhibition, BK also evoked an endothelium-dependent contraction, which was blocked by TP receptor antagonism. In addition, inhibition of COX-1 (but not COX-2) impeded the vasoconstrictor activity of BK and expedited the relaxation induced by the agonist in NOS-intact vessels. These results demonstrate that in the porcine interlobular renal artery BK evokes endothelial COX-1-mediated PGI(2) synthesis, which mainly leads to the activation of TP receptors and a vasoconstrictor response, possibly due to a scarcity of vasodilator activity mediated by IP receptors. Also, our data suggested that the effect of a PGI(2) analog on TP receptors could be reduced compared with that of PGI(2) due to modified structure as with iloprost.

A vasoconstrictor role for cyclooxygenase-1-mediated prostacyclin synthesis in mouse renal arteries

“…1B). It should be noted that in such conditions the only immediate PGI 2 metabolite 6-keto-PGF 1␣ (1 M) was unable to induce any contraction (data not shown), concurring with results reported on porcine interlobular renal arteries (22). In addition, the contraction evoked by the TP receptor agonist U46619 in such treated condition was also more potent in renal than in carotid arteries (Fig.…”

“…Next, we determined whether PGI 2 could be synthesized locally by the renal vasculature. As previously shown in some other vascular beds (21,22), in mouse renal arteries the immunocomplex of PGIS could be clearly seen in endothelium as well as in medial smooth muscle (Fig. 3A).…”

“…In vessels showing robust contraction to PGI 2 , IP receptors may have, if any, only limited functional involvement (19,21,22). Therefore, we determined the effect of PGI 2 or its stable analog and the IP receptor agonist iloprost on mouse renal arteries after TP receptor blockade.…”

“…At the same time, endothelium-derived vasoconstrictor activity has also been found to exist in renal vasculature (5,13,14,23,39). Moreover, our recent studies suggest that in porcine interlobular renal arteries COX-1-mediated endothelial PGI 2 synthesis is responsible for endothelium-dependent vasoconstrictor activity evoked by agonists, such as bradykinin (22). On the other hand, the effect of PGI 2 on a given vascular bed may vary considerably between species (19,38).…”

“…On the other hand, studies also indicate that the endothelial COX-mediated metabolism generates vasoconstrictor products that act on thromboxane-prostanoid (TP) receptors to mediate vasoconstriction (9,14,16,28,30,32,43). Interestingly, PGI 2 can also activate smooth muscle TP receptors (11,21,22,36,38). This has been explained by an excessive production of PGI 2 and/or dysfunction of IP receptors found in conditions such as hypertension (11,36,38).…”