Endothelial cell physiology, perturbations and responses

Adaptability of endothelial orientation to blood flow dynamics--a morphologic analysis

Vascular endothelium has a certain specificity in its anatomical orientation. The long axis of the endothelial cell and the shingle effect of cell process overlapping is always oriented parallel to the direction of blood flow. To determine whether this specific anatomical orientation would be maintained when the direction of blood flow was altered, twenty ilio-femoral vein segments and twenty vascular patches of carotid artery and jugular vein were studied. Valvulotomised ilio-femoral vein segments (n = 20) were interposed into adjacent arteries in a non-reversed fashion (the direction blood flow is reversed to the cell process overlapping). One centimeter-square carotid artery and jugular vein patches (n = 20) were rotated 90 degrees (endothelial cell orientation is perpendicular to the direction of blood flow). Reversal of endothelial cell overlapping to complement the complete reversal of the direction of blood flow exists in the vein graft through re-endothelialisation and endothelial reorientation. The process of endothelial reversal occurred in stages (endothelial cell process retraction, interdigitation, complete reversal) and was completed within 8-16 days. In the vascular patch, endothelial re-orientation occurred in 8 days through cell re-orientation and replacement. Mitosis was not encountered in either study. This report highlights certain functions and the adaptive capability of endothelial cells to complement the direction of blood flow.

Anionic surface properties of aortic and mitral valve endothelium from New Zealand white rabbits

The luminal surfaces of the endothelium lining the two surfaces of the aortic arterial (AAR) and ventricular (AVT), and mitral ventricular (MVT) and atrial (MAT), valve cusps were studied with cationic ferritin (CF) and ferritin (Fer)-conjugated lectins (WGA, RCA, SBA). The arterial (AAR) and ventricular (MVT) surfaces of the aortic and mitral cusps, which are exposed to more turbulent fluid mechanical forces and lower wall shear stresses, had the greatest density of CF labeling. The endothelia of the four surfaces displayed a gradient of decreasing density from the nuclear region to the periphery. Neuraminidase, chondroitinase ABC and AC, heparinase, heparitinase, hyaluronidase (testicular), and pronase E digestions suggested that a significant number of the anionic sites labeled by CF are associated with sialoglycoproteins and glycosaminoglycans such as chondroitin 4/6 sulfates, dermatan sulfates, and heparan sulfates. The localization of WGA receptors on the endothelium of AAR and MVT demonstrated a greater density of sialyl moieties than on the AVT and MAT. There was no binding of Fer-RCA with specificity for D-galactopyranosides or Fer-SBA with affinity for N-acetylglucosamine and D-galactose to the endothelium unless it was first treated with neuraminidase. Hence, sialic acids are shown to be among the more superficial components of this glycocalyx and to be largely responsible for the greater densities over the endothelium of AAR and MVT.

Hemangioendothelioma with intravascular coagulation and ischemic colitis

An infant who presented with a thigh mass and coagulopathy was found to have a hemangioendothelioma. The tumor rapidly enlarged despite accepted therapeutic modalities, and the child died after a sudden cardiac arrest. Postmortem examination revealed a highly invasive tumor mass that had infiltrated the bowel and involved the inferior mesenteric artery, resulting in ischemic colitis of the left colon. A discussion regarding the pathophysiology with respect to endothelial cell properties and other microscopic features of the tumor is presented.

Treatment of delayed radiation necrosis of the brain. A clinical observation

The authors report two cases of delayed radiation necrosis of the brain. In these cases a dramatic clinical and computerized tomographic improvement was noted after the institution of anticoagulant therapy. Based on a review of the literature, a possible causal mechanism is suggested. It was believed from both the clinical observation and the literature review that the anticoagulant agents had a direct effect upon the improvement in these patients. Laboratory data are needed to determine the role of anticoagulant therapy in the treatment of delayed radiation necrosis of the brain.

Interaction of plasmin with endothelial cells

Interaction of human plasmin with a monolayer culture of mini-pig aortic endothelial cells was studied by using the 125I-labelled enzyme. The binding of plasmin was time- and concentration-dependent. Equilibrium between bound and free enzyme was obtained within 90s, and Scatchard analysis indicated a high- and a low-affinity population of binding sites of approx. 1.24 X 10(4) sites/cell having a Kd of 1.4 X 10(-9) M and 7.2 X 10(4) sites/cell with a Kd of 2 X 10(-8) M respectively. Plasmin, bound to cell, was spontaneously released within 2 min, suggesting a rapid equilibrium. Chemical modification of the enzyme with phenylmethanesulphonyl fluoride or pyridoxal 5'-phosphate revealed that neither the active centre nor the heparin-binding site of plasmin was involved in the interaction with the endothelial cell. In terms of endothelial-cell receptors, the binding sites of cells for plasmin and thrombin were different: the two enzymes did not compete with each other, and the pretreatment of cells with neuraminidase or chondroitin ABC lyase resulted in a 50% decrease of thrombin or plasmin binding respectively. Arachidonic acid incorporated into phospholipids of the cell was released by plasmin, but a change in the rate of prostacyclin formation was not measurable. The interaction of plasmin with endothelial cells seems to be specific in the fibrinolytic system, since plasminogen did not bind to these cells under similar conditions.

The cutting-edge microvascular needle. A scanning electron microscopic study

The authors have compared the vascular endothelial damage caused by blunt-tipped microvascular needles as reported previously with that of sharp cutting-edged needles of comparable size. The same four distinct vascular lesions were found with cutting-edged needles as with the blunt-tipped needles. Even though one experimenter made all of the lesions, and all of the tissue was handled in the same fashion, there was much variation in the extent of the intimal damage. Overall, cutting-edged needles produced slightly less intimal tearing and platelet aggregation than blunt-tipped needles, but the difference was not striking.

Modulation of disseminated intravascular coagulation (DIC) by steroidal and non-steroidal anti-inflammatory drugs

Activation of the coagulation systems by endotoxin and release of vasoactive agents are both essential for the production of microthrombosis. Glucocorticoids prevent activation of factor XII by endotoxin in vivo and decrease production of tissue factor by macrophages. NSAID do not interfere with factor XII activation and increase the severity and risks of microthrombosis by inhibiting synthesis and release of protective prostaglandins. On the other hand, prolonged administration of glucocorticoids results in the reduction of the immune defence and fibrinolysis, increases the alpha-adrenergic response to endotoxin and sensitizes to endotoxin-induced intravascular coagulation like NSAID.

The amount of circumscribed brain edema and the degree of post-ischemic neuronal recovery do not correlate well

Fifty-four dogs were exposed to multi-focal ischemia sufficient to maintain suppression of the P1--N1 amplitude of the cortical sensory-evoked response (CSER) for 60 minutes. Subsequently, the P1--N1 amplitude recovery of the CSER was followed for an additional 15, 60, or 120 min while the dogs were treated or left untreated. The combination of PGI2, indomethacin, and heparin promoted a statistically significant augmentation of CSER amplitude return relative to: 1) no treatment; 2) PGI2 alone; 3) indomethacin alone; 4) PGI2 and heparin; 5) indomethacin and heparin; 6) PGI2 and indomethacin. Percentage gray matter water by the wet weight/dry weight technique was significantly elevated in all embolized groups compared to ten non-embolized controls, but the percentage recovery of the CSER did not correlate with the presence or degree of gray matter edema among embolized animals followed for 1 hour. Separation of embolized animals by the presence or absence of "neuron-disabling" flows (defined as 0-15 ml/100 gm/min for gray matter and 0-6 ml/100 gm/min for white matter) did produce significantly different mean CSER percentage recoveries but percentage gray matter water in the two groups was comparable. A proposed explanation of the data is that brain ischemia engenders two parallel processes which may become uncoupled. Ischemia creates metabolic conditions that lead to increased cellular imbibition of water and produces increased vascular leakiness. These perturbations increase brain water content. Concomitantly, there is an occurrence of further metabolic derangements and multifactorial interaction at the blood-endothelial interface which have a direct influence on neuronal function and recovery.

Recovery of prostacyclin production by de-endothelialized rabbit aorta. Critical role of neointimal smooth muscle cells

Prostacyclin (PGI2) synthetic capacity was assayed at the surface of aortas at various intervals after removal of endothelium with a balloon catheter. Results were correlated with morphologic changes in the vessel wall seen by light microscopy, scanning and transmission electron microscopy. To assay PGI2 synthetic capacity, we applied an incubation chamber to the luminal surface of the aortas; after arachidonic acid stimulation we assayed the PGI2 synthesized with a bioassay and radioimmunoassay. PGI2 synthesis in de-endothelialized aortas was determined immediately after balloon-catheter injury and at intervals of 1 h and 2, 4, 15, 35, and 70 d. PGI2 synthesis was low at 1 h and increased over time with levels at 35 and 70 d reaching that of normal artery. Scanning and transmission electron microscopy of de-endothelialized areas showed persistent absence of endothelium with formation of a neointima composed of smooth muscle cells. De-endothelialized aorta was covered with adherent platelets shortly after injury, however several days later only a few platelets adhered to the denuded surface. Results indicated that (a) endothelium is responsible for nearly all PGI2 production at the luminal surface of the normal aorta, (b) de-endothelialized muscular neointima synthesized increasing quantities of PGI2 with time after injury, and (c) increase of PGI2 production at the luminal surface of de-endothelialized aorta correlates with formation of a neointima and with the acquired thromboresistance of the aorta.

Surface topography of stenotic aortic valves by scanning electron microscopy

Surface features of 19 stenotic aortic valves from patients undergoing valve replacement were investigated by scanning electron microscopy. Villi, prominent on five valves, were distributed either singularly or in clusters and differed in shape. Endothelial cells had microvilli and bulbous surface projections. Endothelial disruption with a focal loss of endothelial cells was uniformly observed. Erythrocytes were found scattered over the exposed subendothelial surface or enmeshed within fibrin networks on 11 of the valves. Activated leukocytes were seen on four valves and showed veil-like projections as well as microvilli. Platelets, observed on three valves, displayed pseudopodial formation and hyalomeric spreading, signifying an increased degree of membrane response. Most platelet aggregates were composed entirely of dendritic forms (reversible aggregates), but a few also contained spread forms (irreversible aggreates). Focal deposits of crystalline material, presumably containing calcium, were observed in areas of endocardial disruption.