Decreased vasorelaxation induced by iloprost during acute inflammation in human internal mammary artery.

Cyclooxygenase-2 (COX-2) induction in human internal mammary arteries (IMA) under inflammatory conditions has been associated with attenuated norepinephrine (NE)-induced vasoconstriction. This effect was associated with increased prostaglandin (PG) E ₂ and prostacyclin (PGI ₂ ) releases. The present study was designed to assess the role of these PG and their receptors (EP and IP, respectively) on the vascular reactivity during acute inflammation. Isolated IMA were cultured in the absence (Control conditions) or presence (Inflammatory conditions) of both interleukin-1 beta (IL-1β) and lipopolysaccharide (LPS). The vasorelaxation and the increased content of cyclic adenosine monophosphate (cAMP) induced by iloprost, a PGI ₂ analogue, were significantly reduced under inflammatory conditions and restored in preparations cultured with the IP antagonist (CAY10441). Decreased cAMP levels under inflammatory conditions are due to at least increased phosphodiesterase (PDE) 4B expression. On the other hand, PGE ₂ , thromboxane analogues and EP agonists-induced vasoconstrictions were not affected under inflammatory conditions. No vasorelaxation was observed with PGD ₂ , PGE ₂ or the EP2/4 agonists in pre-contracted IMA. Finally, using RT-qPCR and immunohistochemistry, the COX-2, IP receptor and PGI ₂ synthase (PGIS) were detected. A significant increase of COX-2 and moderate increase of IP mRNA expression was observed under inflammatory conditions, whereas PGIS mRNA level was not affected. This study demonstrates that PGI ₂ /IP receptor signalling and PGI ₂ -induced relaxation are impaired in human IMA during acute inflammation, whereas the responses induced by other prostanoids are not affected. These results could explain some of the mechanisms of vascular dysfunction reported in inflammatory conditions.
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