Heparan sulphate and the binding of lipoprotein lipase to porcine thoracic aorta endothelium

Purified bovine milk lipoprotein lipase was shown to bind to intact porcine aortic endothelium in a specific, saturable fashion. The binding was reversed by exogenous heparin. A single class of binding sites was involved and at saturation 1.24?10¹¹ molecules of lipoprotein lipase / cm² were bound. This represents 0.51?10⁶ enzyme molecules per endothelial cell at a density of 1.2?10³ molecules / μm². The enzyme binding was reduced by prior trypsinisation of the endothelial surface under conditions that removed cell surface glycosaminoglycan chains. The porcine endothelium was shown to have available at its surface 5.4?10¹¹ chains of heparan sulphate plus heparin-like glycosaminoglycans / cm². Such as excess suggests that lipoprotein lipase may interact with approximately one in four of the available heparan sulphate chains.     

Dimensions of the human aortic arch and thoracic aorta studied by nuclear magnetic resonance]

The size of the aortic arch and thoracic aorta was measured in 50 healthy volunteers studied by NMR. In each case the following parameters were measured and statistically elaborated: diameter (in mm) of ascending aorta (between onset and arch beginning), of aortic arch (intermediate zone), of isthmus, of descending aorta (between isthmus and diaphragm), of diaphragmatic isthmus; a mean diameter was also calculated, and for every diameter mean and standard deviation were obtained. Moreover, the length (in mm) of superior and inferior contours of the aortic arch, as the ratio of these two values were obtained. At last, total length of considered aortic tract, area of visualized surface and theoretic volume were obtained. For each parameter a diagram was then plotted, with age in ordinates and values of above mentioned parameters in abscissae. Statistical evaluation allows to affirm that the size of the aorta grows with ageing. On the contrary, the ratio between superior and inferior contour of the aortic arch tends to remain unvaried; this fact seems to disagree with the current opinion that the superior wall of the arch grows with age more than the inferior one.     

Myosin light chain phosphorylation in contraction and relaxation of intact rat thoracic aorta

Myosin light chain phosphorylation in intact rat thoracic aorta was elevated during contraction induced by 0.3 microM norepinephrine, but was not maintained. Addition of 0.5 microM sodium nitroprusside to norepinephrine treated rat aorta strips led to elevation of cyclic GMP levels, relaxation of tension, and dephosphorylation of myosin light chain. Depletion of extracellular calcium or addition of calmodulin antagonists trifluoperazine and W7 diminished the contraction and phosphorylation of myosin light chain by norepinephrine, but did not prevent dephosphorylation by sodium nitroprusside or the elevated levels of cyclic GMP. Isoproterenol, 8-bromo cyclic GMP, and dibutyryl cyclic AMP all caused dephosphorylation of myosin light chain and induced relaxation during the period of development of tone. Eight other proteins had increased phosphorylation following norepinephrine treatment and one protein had less phosphorylation. The different proteins phosphorylated by norepinephrine showed varying degrees of sensitivity to Ca2+-free solution and to the calmodulin antagonists. The pattern of protein phosphorylation caused by sodium nitroprusside was best mimicked by 8-bromo cyclic GMP, rather than isoproterenol and dibutyryl cyclic AMP. These proteins were, generally, unaffected by Ca2+-free solution and the calmodulin antagonists. The present observations support the hypothesis that vasodilators inhibit tone development through myosin light chain dephosphorylation. Furthermore, the nitrovasodilators act through elevation of cyclic GMP and phosphorylation of proteins by cyclic GMP-dependent protein kinase.     

The effects of ionizing radiation on the pulmonary vasculature of intact rats and isolated pulmonary endothelium

We studied the effects of ionizing radiation on the morphology of the pulmonary circulation using an in vivo rat model and an in vitro pulmonary artery endothelial cell model. Gamma radiation was given as either an acute (30 Gy) or fractionated (5 X 6 Gy) dose to one hemithorax of rats. An acute 30-Gy dose delivered resulted in a 70% decrease in pulmonary arterial perfusion, using technetium-99m microaggregated albumin (99mTc-MAA), in the irradiated lung by 2-3 weeks after irradiation. Pulmonary microradiographs, using a barium sulfate perfusion method, obtained 2-3 weeks after irradiation demonstrated widespread loss of capillary filling and segmentation of the vessels. Histologic examination demonstrated intact capillaries, suggesting that the alterations in pulmonary perfusion were at the precapillary level. Similar abnormalities in lung perfusion and morphology were found after delivery of fractionated doses of radiation, but the onset of the changes was delayed, occurring 4-6 weeks postirradiation. Using cultured pulmonary endothelial cell monolayers, cell sloughing and retraction from the surface substrate were observed within 24 h after in vitro delivery of 30 Gy. Similar findings occurred in monolayers given fractionated doses (5 X 6 Gy) of radiation 2-3 days after the final dose. The in vivo animal and in vitro endothelial cell models offer a useful means of examining the morphologic alterations involved in radiation lung vascular damage.     

Smooth muscle cell hypertrophy and hyperplasia in the thoracic aorta of spontaneously hypertensive rats

Changes in the smooth muscle cell compartment (SMCC) of the media layer of the aorta were studied in spontaneously hypertensive (SHR) and in normotensive rats (WKY) of both sexes between 3 to 18 weeks of age. Up to 7 weeks of age, development of the SMCC occured in males and females of the two strains both through a massive increase in cell number and in cell size. In SHR after 7 weeks of age, the development of the SMCC was due to a marked increase in cell size together with an increase in cell number. In contrast during the same period, the development of the SMCC in WKY was associated almost exclusively with an increase in cell size. It is concluded that the presence of a greater number of larger smooth muscle cells contributes to the hypertrophy of the arterial wall of hypertensive animals.     

Endothelium-independent vasodilation effect of di- and tri-peptides in thoracic aorta of Sprague-Dawley rats

The goal of this study was to elucidate the structure-activity relationship for vasodilating peptides and their underlying mechanism. In this study, we synthesized 62 di- and tri-peptides having aromatic amino acid residues (Tyr, Trp and Phe). Among them, only 4 peptides (HW, WH, WL and WV) evoked an apparent vasodilating effect in 50 mM KCl-contracted aortic rings in the descending order of WH>HW>WL>WV; WH showed the vasodilating activity with an EC50 of 3.4 mM. Within our experimental results, it seems likely that Trp residue at the N-terminal would play a role in eliciting vasodilating effect. No appearance of vasodilating effect for stereoisomers of WH with D-configuration revealed that the vessel would recognize the L-configuration of WH. The presence of angiotensin I-converting enzyme (ACE) inhibitor (50 nM enalaprilat) did not affect the WH-induced vasodilating effect, though WH showed a slight ACE inhibitory activity (IC50: 93 microM). The effect was also observed in the endothelium-denuded aortic rings. In contrast, WH provoked a significant displacement to the right in the vasodilating curve in the presence of 30 nM verapamil, while no shift was observed in the presence of 2.5 nM nifedipine. These results indicate that WH, a vasodilating di-peptide, would exert a vasodilation via the suppression of Ca2+ influx into KCl-induced depolarized aortic rings. The present study also suggests that the binding site of WH to the Ca2+ channel may be competitive to that of phenylalkylamine-type voltage-gated L-type Ca2+ channel blocker.     

Cartilaginous metaplasia of the thoracic aorta of control turkeys and exacerbation by beta-aminopropionitrile

Seventeen of sixty distal extremities of the thoracic aortas of 12-week-old control male turkeys and 37 of 40 distal extremities of the aortas of turkeys fed 0.07% beta-aminopropionitrile (BAPN) from 4 to 12 weeks of age contained areas of cartilaginous metaplasia when examined by light microscopy. The cartilaginous areas were generally elongated and located in the subendothelium of control turkeys, but a roundish area of cartilage was occasionally evident in the deep media. The magnitude of chondroplasia was enhanced by feeding BAPN; the extensive lesion usually extended from the subendothelium to deep in the media. Regardless of treatment, chondrocytes were pleomorphic, contained vacuoles, and had cytoplasmic processes. The cells were separated by pools of proteoglycans and connective tissue. The ultrastructure of chondrocytes in the aortas of both treatment groups was typical of this cell type. They had undulations or projections of the cell membranes. The cisternae of endoplasmic reticulum were dilated and contained electron-translucent material which was similar to extracellular proteoglycans. Golgi apparatus, free ribosomes, mitochondria, glycogen granules, filaments, and a centriole also were present in the cytoplasm. The extracellular matrix, which included collagenous and elastic fibers and also delicate fibrils and interconnecting matrix granules, separated adjacent chondrocytes by spaces of varying size.     

The anticoagulant properties of the endothelium studied by the standard venous occlusion test]

Venous occlusion (VO) during which thrombin (Th) is postulated to be generated is routinely used for evaluation of fibrinolytic potential of endothelium (E). This study was performed to find out whether VO can also be used for assessment of anticoagulant function of E. VO was performed in 98 male patients (pts) with ischemic heart disease. Levels of protein C (PrC) which is related to Th binding by thrombomodulin and fibrinopeptide A (FpA)--a marker of presence of free Th--were determined together with some other factors of coagulation and fibrinolysis. Differences between pre- and postVO PrC levels fluctuated from -54.8% to +57.3%. According to reaction of PrC to VO pts were divided into 2 groups: 13 pts with increase or no change and 17 pts with decrease (consumption) of PrC. In pts without PrC consumption there was a significant increase in FpA. In pts with PrC consumption FpA was unchanged. In pts with PrC consumption exceeding its median value for this group (14%) PAI-1 antigen level fell significantly (-8.4 + 4%) during VO. Thus PrC consumption after VO indicates that TH is effectively removed from blood stream by endothelial factors. Absence of consumption of PrC is a sign of ineffective anticoagulant function of E. Increase in PrC level during VO in some pts may be due to its escape from tissue depot.     

Mechanical properties of the extracellular matrix of the aorta studied by enzymatic treatments

The microarchitecture of different components of the extracellular matrix (ECM) is crucial to our understanding of the properties of a tissue. In the study presented here, we used a top-down approach to understand how the interplay among different fibers determines the mechanical properties of real tissues. By selectively removing different elements of the arterial wall, we were able to measure the contribution of the different constituents of the ECM to the mechanical properties of the whole tissue. Changes in the network structure were imaged with the use of two-photon microscopy. We used an atomic force microscope to measure changes in the mechanical properties by performing nanoindentation experiments. We show that although the removal of a key element of the ECM reduced the local stiffness by up to 50 times, the remaining tissue still formed a coherent network. We also show how this method can be extended to study the effects of cells on real tissues. This new (to our knowledge) way of studying the ECM will not only help physicists gain a better understanding of biopolymers, it will be a valuable tool for biomedical researchers studying processes such as wound healing and cervix ripening.     

Damage and regeneration of the endothelium of the aorta in experimental hypercholesterolemia

In dynamics of the experimental hypercholesterolemia in rabbits, peculiarities of endothelial regeneration have been studied. Comparison of proliferative activity level in endotheliocytes with structural-functional state of the endothelial monolayer at atherogenesis makes it possible to consider, that the lesion of the endothelium cannot be regarded as an initiating factor for formation of atherosclerotic lesions. Formation of the lesions in the internal lining of the arteries is preceded by certain disorders in permeability of the endothelial barrier at increasing concentration of cholesterin in blood plasma, accompanying with a sharp activation of the cell proliferative activity. When lipid plates and atherosclerotic plaques are already formed, the processes of the endothelial damage and regeneration occur in parallel. The regeneration is ensured with an intensive proliferation and growth of endotheliocytes onto deendotheliolized areas of the damaged intima.