Characterization of endothelial thromboxane receptors in rabbit aorta

Abstract

An increased synthesis of thromboxane (TX) A2 is associated with a number of cardiovascular diseases including atherosclerosis, unstable angina and hypertension. We previously identified a subgroup of NZW rabbits in which isolated arteries failed to contract to the TX agonists, U46619 or I-BOP. In vascular smooth muscle membranes, there was a significant decrease in TX receptors, termed TP. These rabbits are referred to as vTP− and those with the TP receptor are called vTP+. Because TP receptors are expressed in some types of endothelial cells, the present study was designed to determine whether functional TP receptors are present in endothelial cells cultured from aortas of vTP+ and vTP− rabbits. Radioligand binding studies were performed with 125I-BOP. Aortic endothelial cells from vTP+ rabbits exhibited specific and saturable binding. In contrast, in endothelial preparations from vTP− rabbit aortas, no measurable binding to 125I-BOP was detected. Using an anti-TP receptor antibody, we compared the amount of receptor expressed in endothelial cell lysates obtained from vTP+ and vTP− rabbits. Consistent with the results observed radioligand binding assays, the expression of TP receptor protein was decreased in vTP− compared to vTP+ endothelial cells. An in vitro wound healing assay was used on confluent monolayers of endothelial cells. In the untreated vTP+ cells, the area of the scratch was completely closed by 30 hrs. In the vTP + cells treated with U46619 (3 μM), the rate of closure of the scratch area was reduced with approximately 12% of the scratch area remaining at 30 hrs. Pretreatment with the TP receptor antagonist, SQ 29548 (10 μM) prevented the inhibitory effect of U46619. The rate of closure of the scratch in the vTP− was not altered by U46619. In a separate study, U46619 (3 μM) increased the release of 6-keto PGF1 α , the stable metabolite of prostacyclin, in vTP+ but not vTP− endothelial cells. Pretreatment with SQ29548 (10 μM) or the cyclooxygenase inhibitor, indomethacin (10 μM) blocked the increase in vTP+ endothelial cells. In vascular reactivity studies in aortas from vTP+ rabbits, removal of the endothelium enhanced the vasoconstrictor response to U46619 indicating that activation of endothelial TP receptors may modulate vascular tone via the release of the vasodilator, prostacyclin. The results of this study suggest an important role for endothelial TP receptors in modulating vascular function.

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

“…To selectively and completely inhibit the activity of COX-1, 1 M FR122047 (IC50 values of 0.028 and 65 M for COX-1 and COX-2, respectively) or 0.3 M SC560 (IC50 values of 0.009 and 6.3 M for COX-1 and COX-2 respectively) was used (27,33). Also, the concentration of celecoxib (3 M), CAY10441 (1 M), iloprost, MRE-269 (0.1-1 M), or SQ29548 (10 M) was based on previous reports, in which those compounds were suggested to effectively act on their respective intended enzymes or receptors (8,19,20,23,28,40,44).…”

Hypercholesterolemia and microvascular dysfunction: interventional strategies

“…Further, in hypercholesterolemic mice and diet induced hypercholesterolemic rabbits, compensatory mechanisms evolve to maintain endothelium-dependent dilation as a result of a decrease in NO bioavailability, and appear to involve altered patterns of arachidonic acid metabolism involving both the cyclooxygenase and lipoxygenase pathways [ 11 , 12 , 23 , 41 - 43 ]. Arachidonic acid action within hypercholesterolemia is not limited to metabolite production inducing dilation, but includes the production of thromboxane A 2 (TXA 2 ), a potent vasoconstrictor [ 15 , 44 ]. Hypercholesterolemic animals have shown a limitation to arachidonic acid induced dilation due to an increase in TXA 2 production during metabolism [ 15 ].…”

Arterial thromboxane A2-induced transient contraction after IL-1β exposure

“…10,11 TXA2 is known to have a strong vasoconstrictor effect in addition to its platelet aggregation effect. 12,13 Thus, the involvement of TXA2 in systemic inflammatory conditions, such as infectious diseases, is well recognized. However, there are few reports on the involvement of prostanoids in warm shock.…”