Cyclooxygenase-2–Derived Prostaglandin F _2α Mediates Endothelium-Dependent Contractions in the Aortae of Hamsters With Increased Impact During Aging

Abstract

Abstract-Hypertension and vascular dysfunction result in the increased release of endothelium-derived contracting factors (EDCFs), whose identity is poorly defined. We tested the hypothesis that endothelial cyclooxygenase (COX)-2 can generate EDCFs and identified the possible EDCF candidate. Changes in isometric tension of aortae of young and aged hamsters were recorded on myograph. Real-time changes in intracellular calcium concentrations ([Ca 2ϩ ] i ) in native aortic endothelial cells were measured by imaging. Endothelium-dependent contractions were triggered by acetylcholine (ACh) after inhibition of nitric oxide production and they were abolished by COX-2 but not COX-1 inhibitors or by thromboxane-prostanoid receptor antagonists. 2-Aminoethoxydiphenyl borate (cation channel blocker) eliminated endothelium-dependent contractions and ACh-stimulated rises in endothelial cell [Ca 2ϩ ] i . RT-PCR and Western blotting showed COX-2 expression mainly in the endothelium. Enzyme immunoassay and high-performance liquid chromatography-coupled mass spectrometry showed release of prostaglandin (PG)F 2␣ and prostacyclin (PGI 2 ) increased by ACh; only PGF 2␣ caused contraction at relevant concentrations. COX-2 expression, ACh-stimulated contractions, and vascular sensitivity to PGF 2␣ were augmented in aortae from aged hamsters. Human renal arteries also showed thromboxane-prostanoid receptor-mediated ACh-or PGF 2␣ -induced contractions and COX-2-dependent release of PGF 2␣ . The present study demonstrates that PGF 2␣ , derived from COX-2, which is localized primarily in the endothelium, is the most likely EDCF underlying endothelium-dependent, thromboxane-prostanoid receptor-mediated contractions to ACh in hamster aortae. These contractions involved increases in endothelial cell [Ca 2ϩ ] i . The results support a critical role of COX-2 in endothelium-dependent contractions in this species with an increased importance during aging and, possibly, a similar relevance in humans. Key Words: endothelium-derived contracting factors Ⅲ cyclooxygenase-2 Ⅲ thromboxane-prostanoid receptor Ⅲ aging Ⅲ aorta B esides neuronal and hormonal regulation, vascular tone is modulated locally by a delicate balance between endothelium-derived relaxing (EDRFs) and contracting (EDCFs) factors, 1,2 with the latter being less well-defined but emerging in hypertension, obesity, hyperlipidemia, diabetes, and aging. 3 A number of molecules have been proposed as possible EDCF candidates under pathophysiological conditions. These include prostaglandin (PG)H 2 , thromboxane (TX)A 2 , leukotrienes, endothelin 1, and superoxide anions. The release of these tentative EDCFs can be triggered by acetylcholine (ACh), angiotensins I/II, ADP, and ATP. 4 The contribution of additional cyclooxygenase (COX)-derived metabolites, ie, PGE 2 , PGD 2 , and PGF 2␣ , has been postulated. The precise nature of these EDCFs varies among species and vascular beds. 1,3 Two isoforms of COX have been identified in blood vessels. COX-1 is constitutively expressed and...

Non-steroidal anti-inflammatory drugs attenuate the vascular responses in aging metabolic syndrome rats

“…Meloxicam caused a decrease in NE constriction, which was greater in the Control old rats than young rats ( Figure 3D), suggesting that a COX-2 product is involved and related to age, according to the increase in COX-2 expression during aging ( Figure 1B). We have shown up-regulated in the presence of COX-1 and COX-2 in aortas from MS rats at six months of age, which is in accordance with previous results showing that both isoforms can contribute to endothelial dysfunction [22,53,59] . In several species, some authors have reported that PLA 2 and COX-2 are inflammatory proteins, and their expression is tightly regulated by various mediators [60][61][62] .…”

“…At least, in the rat aorta, EDCFs appear to be COX-1-derived prostanoids generated in the endothelium, which diffuse to contract the underlying vascular smooth muscle by activating thromboxane-prostanoid receptors [53] . Therefore, EDCF diffuses and subsequently stimulates thromboxane-prostanoid receptors in vascular smooth muscle [54] .…”

“…Thus, the mechanism of this effect may be COX-1 inhibition, leading to the release of TXA 2 and prostaglandin F2α, which are vasoconstricting prostanoids [58] . In the arteries of spontaneously hypertensive or diabetic rats, COX-1 expression is up-regulated, and the augmented endothelium-dependent contractions are diminished by COX-1 inhibitors [53] . Meloxicam caused a decrease in NE constriction, which was greater in the Control old rats than young rats ( Figure 3D), suggesting that a COX-2 product is involved and related to age, according to the increase in COX-2 expression during aging ( Figure 1B).…”

Investigation of the functional expression of purine and pyrimidine receptors in porcine isolated pancreatic arteries

“…Endothelial cells can release endothelium-derived contractile factors, which may include thromboxane A 2 , prostaglandin F 2α , leukotrienes and endothelin-1. Thromboxane A 2 and prostaglandin F 2α are released from the endothelium due to the activity of COX-2 [38,39]. The reduction of the contraction to UTP in the presence of DUP 697 indicated the involvement of thromboxane A 2 and prostaglandins in the contraction to UTP.…”

“…The reduction of the contraction to UTP in the presence of DUP 697 indicated the involvement of thromboxane A 2 and prostaglandins in the contraction to UTP. These agents, after being released from the endothelium, may act on their receptors on VSMCs to cause contraction [39]. The different effects of DUP 697 on responses to UTP and ATP further suggest that they are acting on different receptors.…”