Functions and dysfunctions of the vascular endothelium

Endothelium represents a large paracrine gland with an enormous reactive surface. By means of its numerous vasodilation and vasospastic factors it manages the basal and working tonus of vessels and thus also the regional flow and the access of target tissues to hormones and metabolic substrates. It manages also the proliferation and migration of myocytes of the vascular wall and thus its adaptation to overload. The dysfunctional states of endothelium are observed in arterial hypertensions, diabetes, dyslipoproteinaemia, and they grow with age. They are the first stage of atherothrombogenic processes. They manifest themselves by a decreased vasodilation reserve of the vascular wall to strain, insulin and many other stimuli. On the contrary, quite frequently they paradoxically react to physical strain, acetylcholine, histamine, ATP etc. by vascular spasms which can determine vasospastic and microvascular angina pectoris including spasms and occlusions of e.g. coronary arteries in sites of insignificant stenoses with the origin of infarctions. The damaged endothelium, so to explain, conceives these stimuli in accordance with the encoded programme as a stimulus to the protection from haemorrhage during stress (fight or flight) and develops "suicidal" defensive reaction against them which we are nowadays able to modulate by administration of ACE-inhibitors, beta-blockers, hypolipidaemic drugs, inhibitors of cyclooxygenase-1 (30-100 mg of aspirin), Ca-antagonists and antioxidants including numerous non-pharmacological procedures. We can retard or halt the process of atherothrombogenesis and avoid or lower thus the number of sudden vascular ventricular as well as brain episodes, including the congestive heart failures, limb amputations and ischaemic damage of the brain. (Fig. 4, Ref. 70.)     

Osteoporosis in chronic liver disease: pathogenesis, risk factors, and management

The survival of non-dividing (G0) leukaemic lymphocytes in culture is generally too short for their radiosensitivity to be quantitatively assessed, since lethally X-irradiated cells may show a long delay before manifestations of cell death ("interphase death") are seen. Counts of surviving cells will therefore include both lethally-hit cells (apparent survivors), and real survivors which have not been lethally hit. Death rates of irradiated leukaemic and normal cells show great variation between individuals, so that comparisons of radiosensitivity between different cell populations based on surviving cell counts at a single time-point are invalid. In this study the supposed radioresistance of prolymphocytic leukaemia lymphocytes was examined in 6 patients with B-cell disease. Survival curves were plotted from serial observations made over several days after graded X-irradiation (0-1000 cGy). We attempted to interpret these radiation responses in terms of their dose dependence (intrinsic radiosensitivity) and time dependence (cell death rate) characteristics using the best-fitting of four mathematical models, all based on classical "single-hit" target theory. The apparent radioresistance shown in 4 cases could be explained by very slow death rates (T1/2 values 55-205 h) of cells proving otherwise radiosensitive (D37 values 38-123 cGy). Genuine radioresistance was found in only 1 case (actual D37 value above 2000 cGy). By ignoring delayed cell death in clinical assessments, pathological lymphocytes could be mistakenly categorised as resistant to elimination by radiotherapy.     

Presence of T-antigen on the vascular endothelium

Bacterial neuraminidase plays an important role in the pathogenesis of some haemolytic anaemias. It divides neuraminic acid from the red cell surface to expose a hidden antigen (Thomsen-Friedenreich antigen, T). A physiologically circulating antibody can then react with the uncovered T and cause a rapid haemolysis. This study demonstrates the presence of T on human vascular endothelium. Similar to red cells it is exposed by the action of bacterial neuraminidase. The subsequent reaction with the physiological antibody could be involved in the pathogenesis of vascular damage observed in severe cases of bacterial septicaemia.     

Interaction of thrombin and platelets with the vascular endothelium

Thrombin is a potent stimulus for prostacyclin (PGI2) release from the vascular endothelium. Treatment of the endothelium with high concentrations of aspirin to block PGI2 formation was associated with increased platelet adherence in a system employing thrombin and 51Cr-labeled platelets. Addition of exogenous PGI2 to the aspirin-treated endothelium restored platelet adherence to the low baseline values. After an initial exposure of the endothelium to thrombin, the cultured endothelium was unable to respond to a second thrombin stimulus with release of PGI2. During this refractory period, the absence of PGI2 was associated with increased platelet adherence. Thus thrombin, an active coagulant and thrombogenic substance, has the capability to release PGI2, the most potent inhibitor of platelet aggregation known to exist in vivo.     

Toxicological effects of beryllium on platelets and vascular endothelium

The crystal structure of rabbit muscle pyruvate kinase complexed with Mn2+, K+, and pyruvate revealed a binding site of K+ [T. M. Larsen, L. T. Laughlin, H. M. Holden, I. Rayment, and G. H. Reed (1994) Biochemistry 33, 6301-6309]. Sequence comparisons of rabbit muscle pyruvate kinase and pyruvate kinases from Corynebacterium glutamicum and Escherichia coli, which do not exhibit a requirement for activation by monovalent cations, indicate that the only substitutions in the K+ binding site are conservative. Glu 117 in the rabbit muscle enzyme, which is close to the K+ site, is, however, replaced by Lys in these two bacterial pyruvate kinases. The proximity of Glu 117 to K+ in the structure of the rabbit enzyme and conservation of the binding site in the bacterial enzymes which lack a dependence on monovalent cations suggested that a protonated epsilon-amino group of Lys 117 in these bacterial enzymes may provide an "internal monovalent cation." Site-specific mutant forms of the rabbit enzyme corresponding to E117K, E117A, E117D, and E117K/K114Q pyruvate kinase were examined to test this hypothesis. The E117K pyruvate kinase exhibits 12% of the activity of the fully activated wild-type enzyme but is > 200-fold more active than the wild-type enzyme in the absence of activating monovalent cations. Moreover, the activity of E117K pyruvate kinase exhibits no stimulation by monovalent cations in the assay mixtures. Both E117A and E117D pyruvate kinases retain activation by monovalent cations but have reduced activities relative to wild type. The results are consistent with the hypothesis that pyruvate kinases that do not require activation by monovalent cations supply an internal monovalent cation in the form of a protonated epsilon-amino group of Lys. The results also support the assignment of the monovalent cation in the active site of pyruvate kinase.     

Effects of chronic vitamin E deficiency on vascular function--a study of sympathetic nerves, smooth muscle and endothelium of the mesenteric arterial bed of the rat

1. Male rats were deprived as weanlings of dietary vitamin E for 2, 4, 6, 10 and 12 months. Mesenteric arterial beds from these rats and from age-matched controls were isolated and perfused with Krebs solution at a constant flow rate (5 ml min-1). The function of perivascular sympathetic nerves, smooth muscle and endothelium was assessed. 2. At 12 months vitamin E deficient rats exhibited the characteristic symptoms of vitamin E deficiency, namely poor coat condition, muscle wasting, kyphoscoliosis and impaired gait. In the isolated mesenteric arterial bed electrical field stimulation (EFS) of perivascular nerves (4-32 Hz, 90 V, 1 ms, for 30 s) elicited frequency-dependent vasoconstrictor responses which were unaffected by vitamin E deficiency except at 12 months, at which age responses were significantly greater than those of the controls at 24 and 32 Hz (P < 0.01). 3. Exogenous noradrenaline (NA; 0.15-500 nmol) elicited dose-dependent vasoconstriction which was similar in vitamin E-deficient and control preparations at all ages. Potassium chloride (0.15 mmol) also produced similar vasoconstrictor responses in vitamin E-deficient and control preparations at each age. 4. Tone of the preparations was raised by continuous perfusion with methoxamine (4-70 microM), producing similar increases in perfusion pressure in vitamin E-deficient and control preparations at each age. Endothelium-dependent dose-dependent vasodilatation to adenosine 5'-triphosphate was significantly impaired in mesenteric arterial beds from 12 month-old vitamin E-deficient rats compared with the controls (P < 0.05). Relaxation to acetylcholine was not significantly different at any age. 5. Endothelium-independent vasodilatation to sodium nitroprusside was similar in vitamin E-deficient rats and age-matched controls. 6. These results suggest that long term (12 months) deprivation of dietary vitamin E may impair endothelial function in mesenteric arteries of the rat. Sympathetic perivascular nerve constrictor function was increased at 12 months. There were no functionally expressed changes in the vascular smooth muscle, which appears to be more resilient to the effects of oxidative stress in vitamin E deficiency.     

The vascular endothelium: physiopathology and participation in thrombogenesis

Even though homeothermic animals regulate the body temperature, fluctuations up to 2-3 degrees C may occur during physiological conditions. In many species, including the rat, a similar variation can be measured in the brain temperature. Such changes are expressed throughout the brain with a preserved gradient between the warmer basal and cooler dorsal parts. In spite of these recordable physiological changes, spatial learning is quite robust, in that it occurs at brain temperatures between 30 and 39 degrees C. Even drastic cooling (to below 15 degrees C) fails to affect consolidation or storage of information when the animal is tested after rewarming. The physiological temperature fluctuations have significant consequences for electrophysiological responses in the brain. Various bioelectrical signals are more sensitive during warming, axonal conduction is speeded up, and stimulus-elicited transmitter release becomes faster and more synchronized. Action potentials have shorter rise and decay times in warm conditions, and the amplitude becomes slightly smaller. Population responses are differently affected by these changes. Dentate field potentials in response to stimulation of perforant-path fibers appear with shorter latency in warm conditions, and the rate of rise in the field EPSP is increased. Paradoxically, the amplitude of the population spike is reduced. This is due to a combination of reduced amplitude of individual action potentials and reduced efficiency of the summation of groups of action potentials. Due to the large effects of temperature on hippocampal field potentials, it is mandatory that brain temperature changes are monitored and/or controlled whenever such responses are recorded in freely moving and anesthetized animals.     

Wound fluids and the pathogenesis of chronic wounds

PURPOSE: To describe two areas of ongoing investigation into analysis of wound fluids that may eventually lead to better understanding of pathophysiology of chronic wounds and to improved care and treatment. METHODS: Studies used Lowry protein assay, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and zymography to analyze fluids from acute and chronic wounds and serum samples collected from healthy and affected volunteers. SUBJECTS: Thirty-one subjects with ages ranging from 32 to 79 years participated in the research; fluid was collected from chronic wounds in 10 patients (two female, four male, and four unrecorded), fluid was collected from acute mastectomy wounds in 15 patients (all female); blister fluid and blood were collected from two volunteers (one male, one female); and blood for serum preparation was collected from four volunteers (two female, two male). PRIMARY OUTCOME VARIABLES: (1) Fibronectin degradation and (2) expression of matrix metalloproteinases. RESULTS: Fibronectin can be degraded in fluid from chronic wounds but remains intact in blood-derived serum, plasma-derived serum, blister fluid, and mastectomy wound fluid. Matrix metalloproteinases are overexpressed in fluid from chronic wounds compared with mastectomy wound fluid, blood-derived serum, and plasma-derived serum. Matrix metalloproteinases are also expressed of somewhat higher levels in mastectomy fluid than in blood-derived and plasma-derived serum. CONCLUSIONS: These studies identified two factors that may contribute to delayed healing of chronic wound: fibronectin degradation and overexpression of matrix metalioproteinases.     

The pathogenesis, diagnosis and control of Johne's disease

Since 1962, when the control of Johne's disease was last reviewed by the BVA technical development committee there have been no dramatic advances in diagnostic methods for Johne's disease or in methods of control. However, there has been a slow, but steady increase in knowledge of the various aspects of the disease. This article attempts to set out what is known and, more important, not known about the subject.     

HLA-identity--long-term renal graft survival, acute vascular, chronic vascular, and acute interstitial rejection

The object is analysis of the impact of acute and chronic rejection on long-term function in HLA-identical renal transplants performed from 1967 to 1995 by the Saskatchewan Renal Transplant Unit. Forty-eight grafts in 46 patients were studied, of which 39 were first and nine second grafts. Forty-two were for primary and six for secondary renal disease. Thirty-five received azathioprine/prednisone prophylaxis, and 13 received cyclosporine/prednisone with/without azathioprine. Ten-year all graft actuarial survival was 84%, 10-year actuarial graft survival in patients with primary renal disease 90%, and with subsequent graft after first HLA graft failed 97.5%, for age-matched population 98.5% (P=NS). Overall death rate was 8.7% (4/46); in secondary renal disease patients 50% (3/6); in primary renal disease patients 2.5% (1/40, P=0.004). All (9/9) HLA-identical second grafts functioned. Acute rejection with azathioprine/prednisone prophylaxis occurred in 55% (9/17) of grafts treated with <6 pre-graft blood transfusions, with the same prophylaxis but >5 units in 12% (2/16, P=0.015), and with cyclosporine prophylaxis in 13% (2/15, P=0.021). Pulse steroids alone reversed all acute rejection. Grafts failed in 6.2% (3/48), all in primary renal disease patients and one from technical one noncompliance, and one chronic rejection. Graft cost/patient/year amortized over 9 years is $3,855 and comparable dialysis cost would be $35,650; cost for all patients on dialysis for 9 years would be $11,293,320 while comparable graft cost was 1,221,418, a savings of 89.2%. Our conclusions are that HLA-identity associates with the following: (1) a 10-year actuarial survival in primary renal disease that equals that of the age-matched population, (2) uniform success in repeat grafts, (3) virtual absence of chronic rejection despite a high incidence of acute rejection in azathioprine/prednisone grafts that (4) always reversed on pulse steroids, and (5) a cost reduction for grafting of 93.2% compared with dialysis therapy.     

Signaltransduction in vascular endothelium: the role of intracellular calcium and ion channels

Endothelial cells (ECs) provide an ideal surface for blood flow. They inhibit the initiation of blood-clotting, but can also under certain conditions activate this process. ECs influence thrombolysis as well as thrombogenesis. They are "antigen-presenting cells" and play a key role in angiogenesis. In addition, ECs control the permeability of the barrier between bloodvessels and interstitium. One of their most important functions is the regulation of the diameter of the blood vessels and their adaptation to the demanded hemodynamic needs. The production and release of diverse compounds, which interfere with different neighboured target cells, initiate this plethora of functions. Ca2+ signals in endothelial cells play the key role in the release of NO, prostacyclin (PGI2), platelet activating factor (PAF), von Willebrand factor (vWF), tissue plasminogen activator (tPA) and tissue factor pathway inhibitor (TFPI). Changes in the intracellular Ca2+ concentration ([Ca2+]i) are determined by release from intracellular stores and entry through the plasma membrane. The diversity of Ca2+ entry pathways and mechanisms of their control are described. At least two different types of Ca2+ entry channels exist: 1. typical highly Ca2+ selective ion channels which might be activated by depletion of intracellular Ca2+ stores (Ca2+ release-activated Ca2+ channels, CRAC), and 2. Non-selective Ca2+ permeable cation channels (NSC). The latter shares many features with an NSC induced by expression of the protein TRPC3. These channels are only weakly operated by store depletion and require a permissive Ca2+ and Ins(1,4,5)P3 concentration in the cytosol. CRAC channels are possible indirectly involved in Ca2+ entry during mechano-stimulation of ECs. After activation of these entry channels, influx of Ca2+ depends on the driving force. The following ion channels play a pivotal role in regulation of the driving force for Ca2+ entry: an inwardly rectifying K+ channel, identified as Kir2.1, a large-conductance, Ca2+ activated K+ channel (hslo) and at least two Cl- channels (a volume regulated Cl- channel, VRAC, and a Ca2+ activated Cl- channel, CaCC). It will be explained how these ion channels interact in the regulation of the long-lasting (plateau-type) increase in [Ca2+]i which mainly controls NO-synthesis and release. Furthermore, it will be demonstrated that Ca2+ oscillations depend on intracellular events rather than Ca2+ entry from the extracellular space.     

Symptomatic exacerbation of peripheral vascular disease with chronic ambulatory peritoneal dialysis

Details of five patients with exacerbation of the symptoms of peripheral vascular disease on chronic ambulatory peritoneal dialysis (CAPD) are presented. The mechanisms of their vascular complications are discussed and the peripheral arterial sequelae of hypotension induced by CAPD are emphasized. These patients are compared with the other patients in the series of 121 patients. Suggestions for diagnosis and treatment of exacerbations of peripheral vascular disease in patients on CAPD are given.     

Hypertension and endstage renal disease

OBJECTIVE: To review current literature regarding the development of hypertensive renal disease, its epidemiology, and its pathophysiology. This review focuses on strategies to slow or halt the progression of endstage renal disease (ESRD) in hypertension, including the role of blood pressure control, different types of antihypertensive agents, early treatment, and dietary considerations. DATA SOURCES: Information was retrieved from searching the MEDLINE database for articles consisting of epidemiologic studies, clinical studies, and review articles pertaining to hypertension and ESRD. Information also was obtained from the US Renal Data System annual data reports. STUDY SELECTION: Emphasis was placed on clinical trials in the English language addressing issues in hypertension and ESRD. Clinical trials reporting relationships between blood pressure control and ESRD, as well as those comparing different antihypertensive agents, were evaluated. DATA EXTRACTION: The methodology and results from clinical trials were evaluated. Studies were assessed according to the measures of renal function used, baseline data collected, degree of blood pressure control, and antihypertensive therapy. DATA SYNTHESIS: Clinical trials including patients with essential hypertension, diabetes mellitus, and renal insufficiency of various etiologies were evaluated. The recommendations from these evaluations were based on study design and the types of populations used (i.e., blacks vs. whites, diabetics vs. nondiabetics). CONCLUSIONS: Blood pressure control is currently the most important strategy to slow or halt the progression of renal insufficiency in hypertensive individuals. Whether specific antihypertensives are renal protective is still controversial, but results from clinical trials are promising.     

Epidemiology and pathogenesis of Crohn's disease

The onset of Crohn's disease (CD) is more frequent between 15 and 30 years and also has a second peak over 60 years. It female sex it is slightly more prevalent among female. Incidence rates vary in different geographic areas, ranging from 2 to 4 new cases/100,000 inhabitants/year. Prevalence data range from 1.2 to 200,000/100,000. Ethnic differences are beginning to disappear, underlining the role of environmental factors in the genesis of the disease. At the moment the most reliable hypothesis is that CD has a multifactorial pathogenesis: antigenic and environmental factors acting in genetically predisposed patients. According to this hypothesis, first degree relatives of CD patients have a relative risk of disease ranging from 2 to 4. Many infective agents have been associated with its onset and relapse; the most reliable observations are those related to the measles virus. There is an activation of the immunosystem which is shown by abnormal T-cell activation, by the increase of some cytokines and by the expression of adhesion molecules. The role of oral contraceptives and diet as risk factors is controversial. Smoking is the only risk factor positively associated with the onset of CD and its clinical course; this association is specific and dose-related.     

Alteration of vascular endothelium and endothelium smooth muscle interaction after carbogen gas perfusion of isolated rat and guinea pig heart

The aim of the study was to alter the vascular endothelium of the mammalian myocardium with respect to coronary flow regulation and vascular permeability. For this purpose, carbogen gas perfusion (GP) of Langendorff-type isolated rat and guinea pig heart was chosen. Perfusion of the hearts with carbogen gas was possible, as well as replacement of the GP by fluid perfusion. The energetic and mechanical state, the creatine kinase release, and the electron microscopic examination of the rat heart indicated only a moderate to minimal alteration of the cardiomyocytes after GP. As a result of GP a massive alteration of the vascular endothelium could be demonstrated in the rat heart, based on the release of the cytosolic endothelial marker enzyme, purine nucleoside phosphorylase, the partly altered vascular permeability and the morphologically detected endothelial damage to arterioles, capillaries and venules. Moreover, the reduced coronary flow response to short periods of anoxia (rat, guinea pig) and the inverted flow response to serotonin administration with maintained response to sodium nitroprusside (rat) in the post-gas perfusion period reflected an alteration of endothelial smooth muscular interaction in the rat and guinea pig heart. Furthermore, the distensibility of the coronary vasculature was increased in the rat and guinea pig heart in the post-gas perfusion period, where a relative autoregulatory behavior was maintained (rat) or partly maintained (guinea pig) in passively predilated vessels. In conclusion, carbogen gas perfusion of isolated hearts allows to induce preferred alteration of endothelium and endothelium-smooth muscle interaction.     

Vascular clogging, mononuclear cell margination, and enhanced vascular permeability in the pathogenesis of human cerebral malaria

To document histopathologic evidence on the pathogenic mechanism of human cerebral malaria, we used light microscopy to study brain specimens from 23 patients who died of central nervous system involvement with Plasmodium falciparum. Sequestration of parasitized red blood cells (PRBCs) leading to cerebral capillary clogging was seen. In a few specimens, vascular clogging by PRBCs was associated with margination of mononuclear cells. In others, capillaries were virtually empty and lymphocytes and monocytes were seen in apposition (marginated) to the capillary endothelial surface. The endothelial cells appeared plump, hypertrophied, and prominent. The capillary wall appeared thickened by fibrinous material. Massive intercellular brain edema along with extravasated red blood cells, mononuclear cells, and plasmatic fluid was also noticed. In addition to hypoxia induced by PRBC-mediated vascular clogging, marginating mononuclear cells may contribute to the pathogenesis of cerebral malaria. The precise role played by this phenomenon needs further evaluation.