Regional differences in prostaglandin production rates among porcine intrathoracic vessels

Toward engineering a human neoendothelium with circulating progenitor cells

Tissue-engineered vascular grafts may one day provide a solution to many of the limitations associated with using synthetic vascular grafts. However, identifying a suitable cell source and polymer scaffold to recreate the properties of a native blood vessel remains a challenge. In this work, we assess the feasibility of using endothelial progenitor cells (EPCs) found in circulating blood to generate a functional endothelium on poly(1,8-octanediol-co-citrate) (POC), a biodegradable elastomeric polyester. EPCs were isolated from human blood and biochemically differentiated into endothelial-like cells (HE-like) in vitro. The differentiated cell phenotype and function was confirmed by the appearance of the characteristic endothelial cell (EC) cobblestone morphology and positive staining for EC markers, von Willebrand factor, vascular endothelial cadherin, flk-1, and CD31. In addition, HE-like cells cultured on POC express endothelial nitric oxide synthase at levels comparable to aortic ECs. Furthermore, as with mature endothelial cells, HE-like cell populations show negligible expression of tissue factor. Similarly, HE-like cells produce and secrete prostacyclin and tissue plasminogen activator at levels comparable to venous and aortic ECs. When compared to fibroblast cells, HE-like cells cultured on POC show a decrease in the rate of plasma and whole-blood clot formation as well as a decrease in platelet adhesion. Finally, the data show that HE-like cells can withstand physiological shear stress of 10 dynes/cm(2) when cultured on POC-modified expanded poly(tetrafluoroethylene) vascular grafts. Collectively, these data are the foundation for future clinical studies in the creation of an autologous endothelial cell-seeded vascular graft.

Effects of unstimulated polymorphonuclear neutrophils on porcine distal coronary artery tone

Recently, it has been demonstrated that polymorphonuclear neutrophils (PMNs) affect coronary vascular tone. We have reported that unstimulated PMNs constrict the porcine proximal coronary artery. However, the mechanism(s) of interaction between PMNs and coronary artery and the regional differences in susceptibility of the coronary arterial tree have not been fully explored. We examined changes in the isometric tension of porcine distal coronary arterial rings caused by unstimulated PMNs, in which the levels of superoxide anion detected by the cytochrome C method were slight when unstimulated and significant when stimulated with A23187. Unstimulated PMNs relaxed the distal coronary artery and the effect was suppressed by endothelial denudation, indomethacin and the prostacyclin synthetase inhibitor, tranylcypromine. During vasorelaxation, prostacyclin was produced (n=8, with without relaxation; 596 +/- 76/247 +/- 26 pg/ml, p < 0.01) and was considered, therefore, to be the vasodilatory substance responsible for the action. These results suggest that PMNs modulate coronary arterial tone via an interaction between PMNs and endothelium and the release of vasodilating prostaglandins, of which prostacyclin is considered to be one of the substances responsible. Further, the effect differed markedly depending on the site of the coronary artery. In vivo, coronary artery tone is complexly regulated, therefore, the relative contribution of the present PMN-endothelial cell interaction observed in vitro is unclear.

Heterogeneity of [Ca(2+)](i) signaling in intact rat aortic endothelium

Most existing knowledge about [Ca(2+)](i) signaling in vascular endothelium has been based on studies using endothelial cells cultured in vitro. To examine how endothelial cells behave in situ, we have developed a method to monitor single-cell [Ca(2+)](i) from Fura-2-loaded rat aortic segments. Fluorescence ratio images from large numbers of endothelial cells were acquired by using a flow chamber mounted on a dual-wavelength fluorescence microscope. Our results showed that either acetylcholine or histamine reversibly activated the vascular endothelium by eliciting M(3) or H(1) receptor-mediated [Ca(2+)](i) increases, respectively. The acetylcholine-evoked endothelial [Ca(2+)](i) elevation at the branch site (intercostal orifice) was much more pronounced than that at the non-branch area. However, endothelium at the branch site was relatively insensitive to histamine. Both acetylcholine-sensitive and histamine-sensitive endothelial cells were arranged in belts aligned along flow lines and were intercalated with each other. Data analyzed from 400 endothelial cells located at the non-branch site showed drastically heterogeneous [Ca(2+)](i) responses to a fixed concentration of either acetylcholine or histamine, differing by two orders of magnitude in individual cells. As a conclusion, vascular endothelial cells appear to have their own characteristic [Ca(2+)](i) 'fingerprint' to various agonists and they may function coordinately in situ.

Microsphere-induced bronchial artery vasodilation: role of adenosine, prostacyclin, and nitric oxide

We previously found that injection of 15-micron microspheres into the bronchial artery of sheep decreased bronchial artery resistance. This effect was inhibited partially by indomethacin or 8-phenyltheophylline, suggesting that microspheres caused release of a dilating prostaglandin and adenosine. To identify the prostaglandin and confirm adenosine release, we perfused the bronchial artery in anesthetized sheep. In 12 sheep, bronchial artery blood samples were obtained before and after the infusion of 1 x 10(6) microspheres or microsphere diluent into the bronchial artery. Microspheres, but not diluent, decreased bronchial artery resistance by 40% and increased bronchial artery plasma 6-ketoprostaglandin F1 alpha (194.7 +/- 45.0 to 496.5 +/- 101.3 pg/ml), the stable metabolite of prostacyclin, and prostaglandin (PG) F2 alpha (28.1 +/- 4.4 to 46.2 +/- 9.7 pg/ml). There were no changes in PGD2, PGE2, thromboxane B2, adenosine, inosine, or hypoxanthine. Pretreatment with dipyridamole, an adenosine uptake inhibitor, did not affect bronchial artery nucleoside concentrations (n = 7). Microsphere-induced vasodilation was not enhanced by dipyridamole (n = 9) and was not inhibited by either the adenosine receptor antagonist xanthine amine congener (n = 4) or the nitric oxide (NO) synthase inhibitor NG-monomethyl-L-arginine (n = 8). These results do not support a role for either adenosine or NO and suggest that microspheres caused bronchial artery vasodilation through release of prostacylin and an unidentified vasodilator.