Concomitant activation of functionally opposing prostacyclin and thromboxane prostanoid receptors by cyclo‐oxygenase‐1‐mediated prostacyclin synthesis in mouse arteries

Abstract

This study aimed to determine whether cyclo-oxygenase-1 (COX-1) mediates dilatation of mouse arteries via synthesis of prostacyclin (PGI 2 ) and, if so, how PGI 2 (IP) receptors contribute and whether thromboxane prostanoid (TP) receptors are implicated in the process. Mesenteric arteries were isolated from wild-type mice or mice with COX-1 deficiency (COX-1 −/− ). The vasomotor reaction to the COX substrate arachidonic acid (AA) was determined with isometric force measurement, while the in vitro production or the plasma level of the PGI 2 metabolite 6-keto-PGF 1α was analysed with high-performance liquid chromatography-mass spectroscopy or enzyme immunoassay, respectively. Results showed that AA, which evoked endotheliumdependent 6-keto-PGF 1α production, elicited relaxation that was inhibited or enhanced by antagonizing IP or TP receptors, respectively. Also, IP receptor blockade resulted in contraction in response to AA (following NO synthase inhibition), which was prevented by a concomitant TP receptor antagonism. Meanwhile, COX-1 −/− or COX-1 inhibition abolished the in vitro 6-keto-PGF 1α production and reduced the relaxation or contraction observed with AA. Real-time PCR showed that whereas TP receptor mRNAs were detected at similar levels, IP receptor mRNAs were present at higher levels in the branches than in the main stem of the mesenteric artery. In addition, antagonizing the IP receptors enhanced the contraction evoked by PGI 2 in the carotid artery. Also, we noted that COX-1 −/− mice had a reduced basal plasma 6-keto-PGF 1α level. These results demonstrate an explicit vasodilator role for COX-1-mediated endothelial PGI 2 synthesis and suggest that the functionally opposing IP and TP receptors concomitantly mediate the vasomotor reaction to PGI 2 , with the dilator activity of IP receptors being compromised by the vasoconstrictor effect of TP receptors and vice versa.

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

“…First-strand cDNA was synthesized using total RNA (250 ng) and oligo(dT) 15 primers (TakaRa). The PCR primers for TP receptor, IP receptor, and ␣-actin were described previously (19). The specificity of primers was first confirmed with regular RT-PCR.…”

“…For the functional studies, the vessel was cut into 1-mm rings as described previously (21). In some experiments, carotid arteries that have limited IP receptor function and show prominent contraction to endothelial agonists, such as ACh and/or mesenteric arteries, which show potent relaxation to PGI 2, from C57BL/6 mice were prepared for control functional analyses (19,21).…”

“…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). In addition, while mice are commonly used as models to study human diseases, such as hypertension, the exact role of PGI 2 synthesis in their renal arteries still remains to be clearly elucidated.…”

“…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). Moreover, both TP and IP receptors may concomitantly modulate the vasomotor reaction to PGI 2 ; hence, in vessels with limited functional IP receptors the process of PGI 2 synthesis itself is suggested to mediate a vasoconstrictor response even under normal physiological conditions (7,19,21,30).…”

“…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). Moreover, both TP and IP receptors may concomitantly modulate the vasomotor reaction to PGI 2 ; hence, in vessels with limited functional IP receptors the process of PGI 2 synthesis itself is suggested to mediate a vasoconstrictor response even under normal physiological conditions (7,19,21,30).Renal vascular tone plays an important role in controlling systemic blood pressure and balance of body fluid and salts. In the renal vasculature, PGI 2 has been considered as endotheliumderived vasodilator; a decrease in its synthesis is suggested to cause increased renal vascular resistance (12,15).…”