Alterations in bovine endothelial histidine decarboxylase activity following exposure to shearing stresses

Atherosclerosis and endothelial mechanotransduction: current knowledge and models for future research

Endothelium health is essential to the regulation of physiological vascular functions. Because of the critical capability of endothelial cells (ECs) to sense and transduce chemical and mechanical signals in the local vascular environment, their dysfunction is associated with a vast variety of vascular diseases and injuries, especially atherosclerosis and subsequent cardiovascular diseases. This review describes the mechanotransduction events that are mediated through ECs, the EC subcellular components involved, and the pathways reported to be potentially involved. Up-to-date research efforts involving in vivo animal models and in vitro biomimetic models are also discussed, including their advantages and drawbacks, with recommendations on future modeling approaches to aid the development of novel therapies targeting atherosclerosis and related cardiovascular diseases.

Collagen Molecular Damage is a Hallmark of Early Atherosclerosis Development

Remodeling of extracellular matrix proteins underlies the development of cardiovascular disease. Herein, we utilized a novel molecular probe, collagen hybridizing peptide (CHP), to target collagen molecular damage during atherogenesis. The thoracic aorta was dissected from ApoE^-/- mice that had been on a high-fat diet for 0-18 weeks. Using an optimized protocol, tissues were stained with Cy3-CHP and digested to quantify CHP with a microplate assay. Results demonstrated collagen molecular damage, inferred from Cy3-CHP fluorescence, was a function of location and time on the high-fat diet. Tissue from the aortic arch showed a significant increase in collagen molecular damage after 18 weeks, while no change was observed in tissue from the descending aorta. No spatial differences in fluorescence were observed between the superior and inferior arch tissue. Our results provide insight into the early changes in collagen during atherogenesis and present a new opportunity in the subclinical diagnosis of atherosclerosis.

Hemodynamic, Surgical and Oncological Outcomes of 40 Distal Pancreatectomies with Celiac and Left Gastric Arteries Resection (DP CAR) without Arterial Reconstructions and Preoperative Embolization

DPCAR’s short- and long-term outcomes are highly diverse, while the causes and prevention of ischemic complications are unclear. To assess oncological, surgical, and hemodynamic outcomes of 40 consecutive DPCARs for pancreatic (n37) and gastric tumors (n3) (2009−2021), retrospective analyses of mortality, morbidity, survival, and hemodynamic consequences after DPCAR were undertaken using case history data, IOUS, and pre- and postoperative CT measurements. In postoperative complications (42.5%), the pancreatic fistula was the most frequent event (27%), 90-day mortality was 7.5. With 27 months median follow-up, median overall (OS) and progression-free survival (PFS) for PDAC were 29 and 18 months, respectively; with 1-, 3-, and 5-years, the OS were 90, 60, and 28%, with an R0-resection rate of 92.5%. Liver and gastric ischemia developed in 0 and 5 (12.5%) cases. Comparison of clinical and vascular geometry data revealed fast adaptation of collateral circulation, insignificant changes in proper hepatic artery diameter, and high risk of ischemic gastropathy if the preoperative diameter of pancreaticoduodenal artery was <2 mm. DP CAR can be performed with acceptable morbidity and survival. OS and RFS in this super-selective cohort were compared to those for resectable cancer. The changes in the postoperative arterial geometry could explain the causes of ischemic complications and determine directions for their prevention.

Investigation of Wall Shear Stress in Cardiovascular Research and in Clinical Practice-From Bench to Bedside

In the 1900s, researchers established animal models experimentally to induce atherosclerosis by feeding them with a cholesterol-rich diet. It is now accepted that high circulating cholesterol is one of the main causes of atherosclerosis; however, plaque localization cannot be explained solely by hyperlipidemia. A tremendous amount of studies has demonstrated that hemodynamic forces modify endothelial athero-susceptibility phenotypes. Endothelial cells possess mechanosensors on the apical surface to detect a blood stream-induced force on the vessel wall, known as "wall shear stress (WSS)", and induce cellular and molecular responses. Investigations to elucidate the mechanisms of this process are on-going: on the one hand, hemodynamics in complex vessel systems have been described in detail, owing to the recent progress in imaging and computational techniques. On the other hand, investigations using unique in vitro chamber systems with various flow applications have enhanced the understanding of WSS-induced changes in endothelial cell function and the involvement of the glycocalyx, the apical surface layer of endothelial cells, in this process. In the clinical setting, attempts have been made to measure WSS and/or glycocalyx degradation non-invasively, for the purpose of their diagnostic utilization. An increasing body of evidence shows that WSS, as well as serum glycocalyx components, can serve as a predicting factor for atherosclerosis development and, most importantly, for the rupture of plaques in patients with high risk of coronary heart disease.

Arterial Stiffness: Different Metrics, Different Meanings

Findings from basic science and clinical studies agree that arterial stiffness is fundamental to both the mechanobiology and the biomechanics that dictate vascular health and disease. There is, therefore, an appropriately growing literature on arterial stiffness. Perusal of the literature reveals, however, that many different methods and metrics are used to quantify arterial stiffness, and reported values often differ by orders of magnitude and have different meanings. Without clear definitions and an understanding of possible inter-relations therein, it is increasingly difficult to integrate results from the literature to glean true understanding. In this paper, we briefly review methods that are used to infer values of arterial stiffness that span studies on isolated cells, excised intact vessels, and clinical assessments. We highlight similarities and differences and identify a single theoretical approach that can be used across scales and applications and thus could help to unify future results. We conclude by emphasizing the need to move toward a synthesis of many disparate reports, for only in this way will we be able to move from our current fragmented understanding to a true appreciation of how vascular cells maintain, remodel, or repair the arteries that are fundamental to cardiovascular properties and function.

Aortic pulse pressure homeostasis emerges from physiological adaptation of systemic arteries to local mechanical stresses

Aortic pulse pressure arises from the interaction of the heart, the systemic arterial system, and peripheral microcirculations. The complex interaction between hemodynamics and arterial remodeling precludes the ability to experimentally ascribe changes in aortic pulse pressure to particular adaptive responses. Therefore, the purpose of the present work was to use a human systemic arterial system model to test the hypothesis that pulse pressure homeostasis can emerge from physiological adaptation of systemic arteries to local mechanical stresses. First, we assumed a systemic arterial system that had a realistic topology consisting of 121 arterial segments. Then the relationships of pulsatile blood pressures and flows in arterial segments were characterized by standard pulse transmission equations. Finally, each arterial segment was assumed to remodel to local stresses following three simple rules: 1) increases in endothelial shear stress increases radius, 2) increases in wall circumferential stress increases wall thickness, and 3) increases in wall circumferential stress decreases wall stiffness. Simulation of adaptation by iteratively calculating pulsatile hemodynamics, mechanical stresses, and vascular remodeling led to a general behavior in response to mechanical perturbations: initial increases in pulse pressure led to increased arterial compliances, and decreases in pulse pressure led to decreased compliances. Consequently, vascular adaptation returned pulse pressures back toward baseline conditions. This behavior manifested when modeling physiological adaptive responses to changes in cardiac output, changes in peripheral resistances, and changes in local arterial radii. The present work, thus, revealed that pulse pressure homeostasis emerges from physiological adaptation of systemic arteries to local mechanical stresses.

The complex distribution of arterial system mechanical properties, pulsatile hemodynamics, and vascular stresses emerges from three simple adaptive rules

Arterial mechanical properties, pulsatile hemodynamic variables, and mechanical vascular stresses vary significantly throughout the systemic arterial system. Although the fundamental principles governing pulsatile hemodynamics in elastic arteries are widely accepted, a set of rules governing stress-induced adaptation of mechanical properties can only be indirectly inferred from experimental studies. Previously reported mathematical models have assumed mechanical properties adapt to achieve an assumed target stress “set point.” Simultaneous prediction of the mechanical properties, hemodynamics, and stresses, however, requires that equilibrium stresses are not assumed a priori. Therefore, the purpose of this work was to use a “balance point” approach to identify the simplest set of universal adaptation rules that simultaneously predict observed mechanical properties, hemodynamics, and stresses throughout the human systemic arterial system. First, we employed a classical systemic arterial system model with 121 arterial segments and removed all parameter values except vessel lengths and peripheral resistances. We then assumed vessel radii increase with endothelial shear stress, wall thicknesses increase with circumferential wall stress, and material stiffnesses decrease with circumferential wall stress. Parameters characterizing adaptive responses were assumed to be identical in all arterial segments. Iteratively predicting local mechanical properties, hemodynamics, and stresses reproduced five trends observed when traversing away from the aortic root towards the periphery: decrease in lumen radii, wall thicknesses, and pulsatile flows and increase in wall stiffnesses and pulsatile pressures. The extraordinary complexity of the systemic arterial system can thus arise from independent adaptation of vessels to local stresses characterized by three simple adaptive rules.

Vascular adaptation and mechanical homeostasis at tissue, cellular, and sub-cellular levels

Blood vessels exhibit a remarkable ability to adapt throughout life that depends upon genetic programming and well-orchestrated biochemical processes. Findings over the past four decades demonstrate, however, that the mechanical environment experienced by these vessels similarly plays a critical role in governing their adaptive responses. This article briefly reviews, as illustrative examples, six cases of tissue level growth and remodeling, and then reviews general observations at cell-matrix, cellular, and sub-cellular levels, which collectively point to the existence of a "mechanical homeostasis" across multiple length and time scales that is mediated primarily by endothelial cells, vascular smooth muscle cells, and fibroblasts. In particular, responses to altered blood flow, blood pressure, and axial extension, disease processes such as cerebral aneurysms and vasospasm, and diverse experimental manipulations and clinical treatments suggest that arteries seek to maintain constant a preferred (homeostatic) mechanical state. Experiments on isolated microvessels, cell-seeded collagen gels, and adherent cells isolated in culture suggest that vascular cells and sub-cellular structures such as stress fibers and focal adhesions likewise seek to maintain constant a preferred mechanical state. Although much is known about mechanical homeostasis in the vasculature, there remains a pressing need for more quantitative data that will enable the formulation of an integrative mathematical theory that describes and eventually predicts vascular adaptations in response to diverse stimuli. Such a theory promises to deepen our understanding of vascular biology as well as to enable the design of improved clinical interventions and implantable medical devices.

Release of non-mast cell histamine from rat aorta

We previously reported that A23187 induces release of histamine from bovine intrapulmonary vein and provided pharmacological evidence against an involvement of mast cells as the source of histamine. This study was conducted to test more definitively the hypothesis that histamine is released from non-mast cell sources in blood vessels. The effects of A23187 on release of histamine were determined using rat aorta which does not contain mast cells. Aortic rings were mounted for recording of isometric tension, and following exposure to A23187 or vehicle, histamine in the bathing media was measured using enzyme immunoassay. A23187 (100 nmol/l - 10 micromol/l) induced concentration-related release of histamine from rings with endothelium. The accumulation of histamine in the bathing media induced by 10 microM A23187 reached plateau at 60 min (6.2 +/- 1.1 pmol/mg) and was markedly and significantly higher than vehicle control (0.4 +/- 0.1 pmol/mg, p < 0.05). Destruction of endothelium significantly inhibited A23187-induced histamine release (5.5 +/- 1.5 pmol/mg with endothelium, 1.1 +/- 0.3 pmol/mg without endothelium, p < 0.05). The results demonstrate that A23187 induces release of histamine from rat aorta which does not contain mast cells and that the release of histamine is largely dependent on the presence of endothelium.

Dirofilaria immitis: heartworm infection converts histamine-induced constriction to endothelium-dependent relaxation in canine pulmonary artery

Heartworm (Dirofilaria immitis) infection alters the behavior of vascular endothelial cells in vivo and in vitro, with the potential, therefore, to influence vascular function. Histamine, an autocoid implicated in the pathogenesis of parasitic and inflammatory diseases, is vasoactive, and causes endothelium-dependent relaxation in some vascular beds. Experiments were designed to determine if histamine is an endothelium-dependent vasodilator in in vitro rings of canine pulmonary artery from heartworm and control dogs; to elucidate the mechanisms involved in histamine vasoactivity; and to measure circulating levels of histamine. Dose-response relationships to histamine were done in rings of canine pulmonary artery from heartworm and control dogs, in the presence and absence of endothelial cells, the H1 receptor blocker tripelennamine, or the H2 receptor blocker cimetidine. Histamine caused a dose-dependent constriction in control, that was not influenced by endothelial cell removal. However, histamine caused an endothelium-dependent relaxation in heartworm pulmonary artery that was converted to constriction by endothelial cell removal. In heartworm, histamine relaxation was mediated by H2 receptors, but did not appear to involve nitric oxide or cyclooxygenase products. While diseases cause depression of endothelium-dependent relaxation, this is the first report of a disease that changes a constriction response to an endothelium-dependent relaxation.

Evidence that histamine is involved as a mediator of endothelium-dependent contraction induced by A23187 in bovine intrapulmonary vein

This study was initiated to test the hypothesis that histamine can act as an endothelium-derived contracting factor in bovine isolated intrapulmonary vein. The effects of calcium ionophore, calcimycin (A23187), on isometric tension were compared in unstimulated rings of intrapulmonary vein with and without endothelium. A23187 (0.1-10 microM) induced concentration-related contraction when endothelium was present. Destruction of endothelium markedly inhibited A23187-induced contraction. Methylene blue, hemoglobin or NG-methyl-L-arginine significantly enhanced A23187-induced contraction only in venous rings with endothelium consistent with attenuation of the contraction by the concomitant release of endothelium-derived relaxing factor (nitric oxide) [EDRF(NO)]. Histamine H1 receptor antagonists inhibited, and iproniazid enhanced, contraction elicited by A23187. A23187 induced release of greater amounts of histamine from venous rings with than without endothelium. A23187-induced contraction was not mimicked by the mast cell activator, compound 48/80, and was not inhibited by preexposure to compound 48/80 or in the presence of cromolyn or doxantrazole. A23187-induced contraction was not inhibited by pretreatment with indomethacin, phentolamine, lipoxygenase inhibitors or superoxide dismutase. The results indicate that A23187 induces endothelium-dependent contraction in bovine intrapulmonary vein and support histamine as one major mediator involved. The association of destruction of endothelium with an inhibition of both A23187-induced contraction and histamine release is consistent with the endothelium as a source for histamine which can exert a local vasoconstrictor effect in bovine intrapulmonary vein.

Astemizole reduces blood-retinal barrier leakage in experimental diabetes

We examined the potential of astemizole, a histamine H1-receptor antagonist that does not cross the blood-brain barrier, to reverse blood-retinal barrier leakage to albumin in streptozotocin diabetic rats. Four groups of nondiabetic and four groups of diabetic rats received vehicle or astemizole at dosages of 5, 10, or 20 mg/kg body weight for days 22-28 of a 28-day holding period. There were no significant differences in nondiabetic plasma-vitreous albumin ratios between animals receiving vehicle or any of the three astemizole dosages. Only diabetic rats receiving vehicle showed a significant (p < 0.05) 100% increase in the plasma-vitreous albumin ratio over their nondiabetic counterparts. Diabetic rats receiving either 5, 10, or 20 mg/kg astemizole exhibited total normalization of vitreous albumin accumulation, despite persistence of diabetes. These data indicate that astemizole, an H1-receptor antagonist that does not cross the blood-retinal barrier, is effective in reversing blood-retinal barrier leakage of albumin in experimental diabetes.

Blood velocity profiles in the origin of the canine renal artery and their relevance in the localization and development of atherosclerosis

Using a 20-MHz 80-channel pulsed Doppler velocimeter and 30-MHz high-resolution echo ultrasound, we investigated the in vivo hemodynamics at the origin of the renal artery by measuring the velocity profiles and bifurcation geometry of a surgically exposed left renal artery in 10 anesthetized dogs. The angle between the aorta and the renal artery ranged from 60 degrees to 90 degrees (mean, 84 degrees) although the bifurcation did not lie in a single anterodorsal plane and the diameter of the renal artery ranged from 1.5 to 3.5 mm (mean, 2.4 mm). Despite different geometries, the velocity profiles in the different aortorenal bifurcations were similar. Although regions of reverse velocity were observed, the net flow in the renal artery was in the forward direction throughout the cardiac cycle. The peak Reynolds' number was 486 +/- 63. The velocity profiles in the proximal renal artery in the plane parallel to the bifurcation showed velocity vectors directed toward the caudal wall throughout the cardiac cycle. Reverse flow, indicating flow separation, was observed near the cranial wall even during systole. When the probe was placed on the cranial wall perpendicular to the wall, a velocity component from the cranial side to the caudal side was observed. At a distance of four diameters from the renal ostia, velocity profiles were almost parabolic. These results indicate that the velocity pattern near the cranial wall at the renal ostia, at which atherosclerotic lesions are prone to develop, are characterized by 1) a low time-averaged shear rate, 2) separation of the flow, and 3) a time-varying oscillation of the flow.

Fluid shear stress as a mediator of osteoblast cyclic adenosine monophosphate production

Effects of interstitial fluid flow on osteoblasts were investigated. Intracellular cyclic adenosine monophosphate (cAMP) levels were monitored in cultured osteoblasts subjected to shear rates ranging from 10 to 3,500 sec-1. Cyclic AMP levels were significantly increased at all shear rates from 1 pmole/mg protein to 10-16 pmole/mg protein. Osteoblasts subjected to a shear rate of 430 sec-1 for 0.5-15 minutes exhibited elevated levels (12-fold) of intracellular cAMP, which were sustained throughout the perfusion period. Osteoblasts were three times more sensitive to flow stimulation than human umbilical vein endothelial cells and baby hamster kidney fibroblasts, which also displayed higher cAMP levels (4-fold) after exposure to flow. To distinguish streaming potential effects from shear stress effects, viscosity was increased 5-fold by addition of neutral dextran to the perfusing medium. Shear stress is a function of viscosity, and streaming potentials are not for a given shear rate. The mechanism of this cellular response to flow was shown to be shear stress dependent. Inhibition of cyclooxygenase by 20 microM ibuprofen completely inhibited the flow-dependent cAMP response, indicating the cAMP response is mediated by prostaglandins. Our results suggest that fluid flow induced by mechanical stress may be an important mediator of bone remodeling.

Cytoplasmic calcium response to fluid shear stress in cultured vascular endothelial cells

Vascular endothelial cells modulate their structure and functions in response to changes in hemodynamic forces such as fluid shear stress. We have studied how endothelial cells perceive the shearing force generated by blood flow and the substance(s) that may mediate such a response. We identify cytoplasmic-free calcium ion (Ca++), a major component of an internal signaling system, as a mediator of the cellular response to fluid shear stress. Cultured monolayers of bovine aortic endothelial cells loaded with the highly fluorescent Ca++-sensitive dye Fura 2 were exposed to different levels of fluid shear stress in a specially designed flow chamber, and simultaneous changes in fluorescence intensity, reflecting the intracellular-free calcium concentration [( Ca++]i), were monitored by photometric fluorescence microscopy. Application of shear stress to cells by fluid perfusion led to an immediate severalfold increase in fluorescence within 1 min, followed by a rapid decline for about 5 min, and finally a plateau somewhat higher than control levels during the entire period of the stress application. Repeated application of the stress induced similar peak and plateau levels of [Ca++]i but at reduced magnitudes of response. These responses were observed even in Ca++-free medium. Thus, a shear stress transducer might exist in endothelial cells, which perceives the shearing force on the membrane as a stimulus and mediates the signal to increase cytosolic free Ca++.

Sex mediated lipid metabolism in human aortic smooth muscle cells

When human aortic smooth muscle cells in culture were treated with pharmacological doses of estrogen and testosterone for 48 hrs, the rate of cholesterol synthesis measured both by acetate incorporation and the 3, hydroxy 3-methylglutaryl Co enzyme A reductase (HMG-CoA) activity declined significantly as compared to control. However, the rate of cholesterol esterification increased by 132% and 45% in response to testosterone and estrogen respectively. Also, acetate incorporation into fatty acids and fatty acid synthetase enzyme activity increased by hormonal treatment but remained in the free form especially by estrogen. Testosterone treatment resulted in more esterification (p less than .025) of fatty acid than estrogen treatment. Incubation with hormones for 48 hrs resulted in enhanced uptake of 14C-labeled cholesterol along with increased accumulation of cellular cholesterol. Increased synthesis of phospholipid and triglyceride by estrogen may be responsible for excretion of cellular sterol and fat. These results indicate that sex-hormones have an important effect on the regulation of lipid metabolism in human aortic cells.

Cultured bovine aortic endothelial cells show increased histamine metabolism when exposed to oscillatory shear stress

Oscillatory shear stress applied to the lining of blood vessels causes endothelial cell injury, one of the essential postulated prerequisites to the development of atherosclerosis. The purpose of this investigation was to study effects of shear stress on bovine aortic endothelial cells (BAEC), in vitro, for varying lengths of time (6 h, 12 h, 24 h) on BAEC histamine content (HC) and histidine decarboxylase activity (HD). Low intensity stress (1.6 dynes/cm2) as well as intermediate and high intensity shear stresses (3.5 dynes/cm2 and 7.6 dynes/cm2) resulted in an accelerated HD (281%) and elevated HC (144%). These data indicate that oscillatory shear stress produces increases in histamine metabolism.

Effects of inflammatory agents on endothelial lysosomal fragility and their inhibition by anti-inflammatory drugs

1. Endothelial cells from human umbilical veins were maintained in tissue culture. The fragility of lysosomal membranes were studied by microdensitometry. 2. Histamine (50 microM to 10 mM), 4-methylhistamine (100 nM to 10 mM) and dimaprit (100 nM to 10 mM) increased lysosomal fragility. 2-Thiazolylethylamine and 2-pyridylethylamine (100 nM to 10 mM) had no effect. 3. Prostaglandins E1 and E2 (3 nM to 30 microM) and prostaglandin F2 alpha (2 nM to 20 microM) had no direct effect. Low concentrations of prostaglandins E1 and E2 inhibited the fragility induced by histamine 100 microM. 4. Bradykinin (100 nM to 100 microM) decreased fragility. 5. The increase in fragility induced by histamine 100 microM or dimaprit 100 microM was inhibited by cimetidine (100 microM to 1 mM) but not by mepyramine (1 microM to 1 mM). 6. Pretreatment with indomethacin, hydrocortisone, ibuprofen and sodium salicylate caused a dose-dependent inhibition of histamine-induced fragility. Threshold concentrations were 1 pM, 100 pM, 10 nM and 10 microM, respectively. 7. Lignocaine (1 microM to 1 mM) had no direct effect and did not decrease histamine-induced fragility.

Blood-brain barrier dysfunction to peroxidase after air embolism, aggravated by acute ethanol intoxication

Ethanol-intoxicated and non-intoxicated rats were injected with horseradish peroxidase and Evan's blue-labelled albumin and given a small air embolus in the right common carotid artery after ligation of the external carotid branch. In both ethanol-intoxicated and non-intoxicated rats, some endothelial cells, mainly in arteries and arterioles, showed a diffuse distribution of peroxidase in the cytoplasm. In some arterioles with a diffuse endothelial distribution of peroxidase there was a detachment of endothelial cells from the vessel wall, with an exposure of the adluminal basement membrane to blood elements. This endothelial detachment was mainly observed in ethanol-intoxicated rats. The vascular basement membranes underlying detached endothelial cells contained peroxidase, both in ethanol-intoxicated and in non-intoxicated rats. There was a considerable leakage of peroxidase via endothelial pinocytotic vesicles into the vascular basement membranes, mainly in arterioles, but also in capillaries and venules of the embolised hemisphere. This transendothelial pinocytotic transport of peroxidase was more prominent in ethanol-intoxicated than in non-intoxicated rats.

Ultrastructural studies on blood-brain barrier dysfunction after cerebral air embolism in the rat

Male albino rats were anaesthetized with diazepam, injected with horseradish peroxidase and Evans blue-labeled albumin and given an embolus of 0.01 ml air in the right common carotid artery after ligation of the external carotid branch. The pial arteries of the right cerebral hemisphere were stained blue, particularly the middle cerebral artery and its main arterial branchlets. Ultrastructurally, some endothelial cells in the right middle cerebral artery, small arteries and arterioles showed a diffuse distribution of horseradish peroxidase in their cytoplasm, although these vessels only occasionally showed peroxidase in their basement membranes. Other endothelial cells in these arterial branchlets showed few if any signs of a diffuse distribution of peroxidase but displayed several pinocytotic vesicles and occasionally trans-endothelial channels filled with peroxidase, sometimes with a slight leakage of peroxidase into adjacent basement membranes and neuropil. Scattered pinocytotic vesicles were observed in capillaries and venules, but there was usually no extravasation of peroxidase around these vessels.

Scanning electron-microscope studies of the endothelium of aortic allografts in the rabbit: effect of azathioprine, prednisolone and promethazine on early cellular invasion

Aortic allografts in rabbits were observed by scanning electron microscopy 24 hr after transplantation. The extent of the leucocytic invasion could be precisely and reproducibly measured. Azathioprine and prednisolone, whether alone or in combination, given on three occasions--10 hr before, immediately after and again 10 hr after surgery, significantly inhibited the cellular invasion. Promethazine produced a slight, but not statistically significant, effect.

Enhanced blood-brain barrier leakage to evans blue-labelled albumin after air embolism in ethanol-intoxicated rats

Control and ethanol-intoxicated rats were given a small air embolus in the right common carotid artery after ligation of the external carotid branch. The extravasation of Evans blue-labelled albumin (EBA) was studied. Control rats dispalyed a slight extravasation of EBA through arteries and arterioles at the surface of the right hemisphere with a slight spread into adjacent brain parenchyma. Additionally, ethanol-intoxicated rats showed a great leakage through small blood vessels even deep in the right hemisphere and a blue-staining of most of the embolized hemisphere. Thus it was shown that during embolization, ethanol increases the vascular permeability to macromolecules. It is proposed that this phenomenon mainly is due to injury to the endothelial cells.

Hyperreactive arterial endothelial cells: a clue for the treatment of atherosclerosis

Arterial endothelial cells, which are capable of phagocytizing carbon particles of the same size as beta- and pre-beta-lipoprotein, were found only in endothelial cells of arterial segments susceptible to atheromatous changes in susceptible animal species, and the distribution closely corresponded to the susceptibility. The distribution of such endothelial cells is dense in large arteries, in the openings to their branches, especially in downstream portions, of rabbits, hens, and cocks; however, the distribution is relatively scanty in arteries of rhesus monkeys and is very scanty in dogs. Carbon particles were also rare in the suckling rabbit and tended to increase with age. They were not found in Wistar rats but were found in spontaneously hypertensive rats, which showed a characteristically diffuse distribution, even in relatively small arteries. The carbon particles, phagocytized, were released to the subendothelial space but were difficult to pass through the internal elastic lamina and tended to stagnate there for more than one month. The authors therefore call these cells hyperreactive endothelial cells. Various vasoactive substances, such as angiotensin II, histamine, and serotonin, significantly enhanced the phagocytic activities of arotic endothelial cells in rabbits; epinephrine and norepinephrine also slightly enhanced these activities. Various smooth muscle relaxants, such as ATP, pyridinol carbamate (ATP synthesis-enhancing substance), cycli-AMP, dibutyryl cycli-AMP, phthalazinol (cyclic-AMP phosphodiesterase inhibitor), iproveratril (calcium entry-inhibiting substance), colchicine, and vinblastine, with their different modes of action, commonly inhibited phagocytic activities, a finding that suggests a significant role for contractile protein in the permeability problem of atherogenesis. The atheromatous lesions of cholesterol-fed rabbits exhibited a striking increase in hyperreactive endothelial cells, accompanied by a marked rise in the activity of low-Km cyclic-AMP phosphodiesterase activity in atheromatous lesions and adjacent muscular layers, especially in rabbits with rapidly progressing atheroma.

Rabbit aortic histamine synthesis following short-term cholesterol feeding

The histidine decarboxylase (HD) activity of thoracic and abdominal aortic segments obtained from male, Dutch-belted rabbits fed a diet containing 0.5 per cent cholesterol for periods of either 2 or 4 weeks was examined. Mean thoracic aortic HD activities, expressed as histamine-forming capacity (HFC), were 3911 plus or minus 492, 6254 plus or minus 656, and 6215 plus or minus 878 dpm/100 mg benzenesulfonylhistamine (BSH) for the control group and from rabbits fed cholesterol for 2 and 4 weeks, respectively. Both treatment means were significantly higher than the control (P smaller than 0.05). Similar examination of abdominal aortic HD activities yielded mean HFC's of 4029 plus or minus 399, 5694 plus or minus 521, and 4762 plus or minus 902 dpm/100 mg BSH for control animals and those of the 2- and 4-week treatment groups, respectively. The difference between mean HFC's of the control and 2-week treatment group was significant (P smaller than 0.05). All increases occurred in the absence of either aortic structural alterations or any lipid deposition. These results give credence to the concept that the atherogenic process represents, at least in part, a delayed-prolonged inflammatory response phenomenon of the arterial wall.