Effects of sodium salicylate on epithelial cells of the rectal mucosa of the rat: A light and electron microscopic study

Using a ligation method, rat rectal epithelium was exposed to 2% sodium salicylate, and light and electron microscopic methods were used to assay for: 1) permeability of the epithelium to a marker dye, trypan blue, and 2) damage expressed in terms of disruption of the epithelial surface. Rectal mucosa was exposed to salicylate at pH 4.8, 7.0, and 9.0, and the effects of pretreatment with phlorizin were also studied. Results indicated that 2% sodium salicylate does very little damage to rectal epithelial cells at pH 7.0 while enhancing their permiability to trypan blue, an effect that is reversed upon washing out the sodium salicylate. The major cellular change induced by salicylate was a reduction in the length or distribution of glycocalyx filaments on microvilli of epithelial cells. It was also noted that pretreatment with phlorizin counteracted some of the effects of salicylate treatment.     

Immune complex induced pancreatitis: effect of BN 52021, a selective antagonist of platelet-activating factor

A model of acute pancreatitis was developed by induction of an immune complex mediated hypersensitivity reaction in rats. This acute inflammatory reaction was characterized by intense interstitial edema, neutrophil infiltration and margination, and congestion of small vessels whereas serum amylase levels remained unchanged. Microscopic examination of the pancreatic tissue revealed the presence of immune complex deposition around blood vessels and ducts. Vascular permeability, as measured by Evan's blue extravasation increased by 6 fold. In addition, circulating platelets dropped to 50% of normal levels. Injection of platelet-activating factor (PAF) in the peritoneal cavity of rats also produced an increase in vascular permeability in the pancreas. A selective PAF-antagonist, BN 52021 reduced by approximately 50% the increase in vascular permeability produced by immune complex in the pancreas as well as that elicited by intraperitoneal injection of PAF. These results suggest that PAF plays a role in the pathological manifestations of immune complex-mediated pancreatitis.     

Segmental pulmonary vascular resistance in progressive hydrostatic and permeability edema

We used the in situ blood-perfused left lower lobe preparation of the dog to examine the effect of hydrostatic and permeability edema on the slope and intercept of the vascular pressure-flow (P/Q) relationship and on the longitudinal distribution of vascular resistance with the arterial and venous occlusion technique. Hydrostatic edema (HE) was induced by raising the venous pressure, and permeability edema (PE) was induced with alpha-naphthylthiourea. When the hematocrit (Hct) of the perfusate was kept normal (approximately 40%), HE had no significant effect on either the slope or the intercept of the P/Q relationship or on the distribution of vascular resistance. PE caused a small increase in the intercept of the P/Q relationship and a small rise in the resistance of the vessels in the middle segment. In another series of HE experiments in which Hct was allowed to increase during edema formation, there was a marked increase in vascular resistance. We conclude that edema per se does not increase vascular resistance significantly and that the increases in vascular resistance which were observed previously by other investigators in the isolated lungs may be due to increases in blood hematocrit.     

Role of sulfhydryls and early vascular lesions in gastric mucosal injury

This paper reviews the recently discovered role of sulfhydryls and early vascular injury in the pathogenesis of acute gastric mucosal injury. In the rat ethanol caused a dose-dependent decrease in nonprotein sulfhydryl concentration in the gastric mucosa within 1-5 min following an intragastric dose. These biochemical changes were accompanied by increased vascular permeability in the glandular stomach as revealed by the measurement of extravasated Evans blue injected i.v. prior to the administration of ethanol. Morphologic evidence of vascular injury was provided by labelling of damaged blood vessels in the stomach following the i.v. administration of colloidal particles in the form of india ink or monastral blue. The functional and structural damage to capillaries and venules in the glandular stomach was also maximal within 1-6 min after 1 ml of 75 or 100% ethanol given orally. Pretreatment with sulfhydryl (SH) containing drugs (e.g., L-cysteine, N-acetyl-L-cysteine, cysteamine, dimercaprol) or prostaglandin (PG) F2 beta prevented the ethanol-induced increase in vascular permeability, the labelling of blood vessels with vascular tracers, and the subsequent haemorrhagic erosions. The desquamation of superficial epithelial cells, however, was not markedly modified by either SH or PG compounds. This organoprotective effect of SH and PG drugs was virtually counteracted in adrenalectomized rats that exhibited "vascular fragility". Glucocorticoid treatment restored the response of adrenalectomized animals. Thus, a SH- and glucocorticoid-sensitive early vascular injury seems to be of major significance in the pathogenesis of haemorrhagic gastric erosions and SH-containing compounds represent a new group of cytoprotective or organoprotective agents.     

Angiopoietin-1 protects the adult vasculature against plasma leakage

Pathological increases in vascular leakage lead to edema and swelling, causing serious problems in brain tumors, in diabetic retinopathy, after strokes, during sepsis and also in inflammatory conditions such as rheumatoid arthritis and asthma. Although many agents and disease processes increase vascular leakage, no known agent specifically makes vessels resistant to leaking. Vascular endothelial growth factor (VEGF) and the angiopoietins function together during vascular development, with VEGF acting early during vessel formation, and angiopoietin-1 acting later during vessel remodeling, maturation and stabilization. Although VEGF was initially called vascular permeability factor, there has been less focus on its permeability actions and more effort devoted to its involvement in vessel growth and applications in ischemia and cancer. Recent transgenic approaches have confirmed the profound permeability effects of VEGF (refs. 12-14), and have shown that transgenic angiopoietin-1 acts reciprocally as an anti-permeability factor when provided chronically during vessel formation, although it also profoundly affects vascular morphology when thus delivered. To be useful clinically, angiopoietin-1 would have to inhibit leakage when acutely administered to adult vessels, and this action would have to be uncoupled from its profound angiogenic capabilities. Here we show that acute administration of angiopoietin-1 does indeed protect adult vasculature from leaking, countering the potentially lethal actions of VEGF and inflammatory agents.     

Alterations of filtration coefficients in pulmonary edema of different pathogenesis.

Different pathomechanisms in the development of pulmonary edema are being discussed. We investigated the effect of pathogenetically varying forms of edema on lung vascular barrier function in isolated cell-free perfused rabbit lungs. As an index of permeability, capillary filtration coefficients (Kfc) were determined from the slope of lung weight change over periods of stepwise venous pressure elevation (5, 7.5, and 10 mmHg) before (controls) and 60 min after edema induction. Edema was induced by venous congestion (n = 6), by application of arachidonic acid in the presence of diclofenac sodium (n = 6), and by elastase application (n = 6). Control values ranged from 0.28 to 0.51 ml.min-1 x mmHg-1 x 100 g-1. Kfc was significantly enhanced after edema induction up to 243% of control value in the hydrostatic edema, 357% in the arachidonic acid edema, and 594% in the elastase edema. When the alterations in capillary filtration due to the different types of edema were compared, Kfc was significantly higher in the proteinase edema, indicating an irreversibly damaged barrier function. These data exemplify different pathophysiological characteristics due to the pathogenesis of interstitial edema formation.     

Effect of forskolin on alterations of vascular permeability induced with bradykinin, prostaglandin E1, adenosine, histamine and carrageenin in rats

The effect of the diterpene forskolin on vascular permeability alone and in combination with bradykinin, prostaglandin E1, adenosine or histamine has been investigated in rats. Vascular permeability in rat skin was measured using [125I]-labelled bovine serum albumin ([125I]BSA) as a tracer. In addition, the effect of forskolin on footpad edema induced by the injection of a mixture of 2% carrageenin was determined. Forskolin caused a marked potentiation of the increase in vascular permeability in rat skin elicited by the intradermal injection of histamine or bradykinin. However, forskolin caused a significant suppression of the prostaglandin E1-induced vascular permeability response and at a low concentration suppressed the response to adenosine. Forskolin greatly potentiated the footpad edema induced with carrageenin in rats. Intravenous administration of the enzyme bromelain, which reduces plasma kininogen levels, inhibited the footpad edema induced with carrageenin or with a mixture of carrageenin and forskolin. Parenteral administration of a prostaglandin synthetase inhibitor, indomethacin, suppressed the footpad edema induced with carrageenin, but did not inhibit the footpad edema induced with a mixture of carrageenin and forskolin. An antihistamine, cyproheptadine, had no effect on carrageenin-induced footpad edema either in the presence or absence of forskolin. These results suggest that both bradykinin and prostaglandins are essential for the development of carrageenin-induced footpad edema and that bradykinin plays an important role in the potentiative effect of forskolin on footpad edema induced with carrageenin in rats.     

Enhancing effects of salicylate on tonic and phasic block of Na+ channels by class 1 antiarrhythmic agents in the ventricular myocytes and the guinea pig papillary muscle

OBJECTIVE: To study the interaction between salicylate and class 1 antiarrhythmic agents. METHODS: The effects of salicylate on class 1 antiarrhythmic agent-induced tonic and phasic block of the Na+ current (INa) of ventricular myocytes and the upstroke velocity of the action potential (Vmax) of papillary muscles were examined by both the patch clamp technique and conventional microelectrode techniques. RESULTS: Salicylate enhanced quinidine-induced tonic and phasic block of INa at a holding potential of -100 mV but not at a holding potential of -140 mV; this enhancement was accompanied by a shift of the hinfinity curve in the presence of quinidine in a further hyperpolarized direction, although salicylate alone did not affect INa. Salicylate enhanced the tonic and phasic block of Vmax induced by quinidine, aprindine and disopyramide but had little effect on that induced by procainamide or mexiletine; the enhancing effects were related to the liposolubility of the drugs. CONCLUSIONS: Salicylate enhanced tonic and phasic block of Na+ channels induced by class 1 highly liposoluble antiarrhythmic agents. Based on the modulated receptor hypothesis, it is probable that this enhancement was mediated by an increase in the affinity of Na+ channel blockers with high lipid solubility to the inactivated state channels.     

Brain edema in diseases of different etiology

Cerebral edema is a potentially life-threatening complication shared by diseases of different etiology, such as diabetic ketoacidosis, acute liver failure, high altitude exposure, dialysis disequilibrium syndrome, and salicylate intoxication. Pulmonary edema is also habitually present in these disorders, indicating that the microcirculatory disturbance causing edema is not confined to the brain. Both cerebral and pulmonary subclinical edema may be detected before it becomes clinically evident. Available evidence suggests that tissue hypoxia or intracellular acidosis is a commonality occurring in all of these disorders. Tissue ischemia induces physiological compensatory mechanisms to ensure cell oxygenation and carbon dioxide removal from tissues, including hyperventilation, elevation of red blood cell 2,3-bisphosphoglycerate content, and capillary vasodilatation. Clinical, laboratory, and necropsy findings in these diseases confirm the occurrence of low plasma carbon dioxide partial pressure, increased erythrocyte 2,3-bisphosphoglycerate concentration, and capillary vasodilatation with increased vascular permeability in all of them. Baseline tissue hypoxia or intracellular acidosis induced by the disease may further deteriorate when tissue oxygen requirement is no longer matched to oxygen delivery resulting in massive capillary vasodilatation with increased vascular permeability and plasma fluid leakage into the interstitial compartment leading to edema affecting the brain, lung, and other organs. Causative factors involved in the progression from physiological adaptation to devastating clinical edema are not well known and may include uncontrolled disease, malfunctioning adaptive responses, or unknown factors. The role of carbon monoxide and local nitric oxide production influencing tissue oxygenation is unclear.     

Hyperoxia causes angiopoietin 2-mediated acute lung injury and necrotic cell death

The angiogenic growth factor angiopoietin 2 (Ang2) destabilizes blood vessels, enhances vascular leak and induces vascular regression and endothelial cell apoptosis. We considered that Ang2 might be important in hyperoxic acute lung injury (ALI). Here we have characterized the responses in lungs induced by hyperoxia in wild-type and Ang2-/- mice or those given either recombinant Ang2 or short interfering RNA (siRNA) targeted to Ang2. During hyperoxia Ang2 expression is induced in lung epithelial cells, while hyperoxia-induced oxidant injury, cell death, inflammation, permeability alterations and mortality are ameliorated in Ang2-/- and siRNA-treated mice. Hyperoxia induces and activates the extrinsic and mitochondrial cell death pathways and activates initiator and effector caspases through Ang2-dependent pathways in vivo. Ang2 increases inflammation and cell death during hyperoxia in vivo and stimulates epithelial necrosis in hyperoxia in vitro. Ang2 in plasma and alveolar edema fluid is increased in adults with ALI and pulmonary edema. Tracheal Ang2 is also increased in neonates that develop bronchopulmonary dysplasia. Ang2 is thus a mediator of epithelial necrosis with an important role in hyperoxic ALI and pulmonary edema.     

Effect of the superoxide dismutase inhibitor, diethyldithiocarbamate, on the cytotoxicity of mitomycin antibiotics

Mitomycin C (MC) and its structural analogs porfiromycin (PM), BMY-25282 and BL-6783 are toxic to EMT6 cells under aerobic and hypoxic conditions. The mitomycin antibiotics are hypothesized to exert cytotoxicity under hypoxic conditions by cross-linking DNA following reductive activation, while aerobic cytotoxicity may involve DNA cross-linking by these agents and/or damage due to the generation of oxygen radicals. Previous findings (Pritsos and Sartorelli, 1986) indicated that the rank order of cytotoxicity for a series of mitomycins was the same as the rank order for the rate of oxygen consumption induced by these agents. As an additional approach to explore the role of oxygen radicals in the aerobic cytotoxicity of the four agents studied, EMT6 cells were treated with the mitomycins in the presence of the superoxide dismutase inhibitor diethyldithiocarbamate (DETC). DETC, which decreased superoxide dismutase activity in EMT6 cells, increased the cytotoxicity of BMY-25282 and BL-6783 by half an order of magnitude, but did not affect the toxicity of PM or MC to these cells. DNA cross-links, a proposed cytotoxic lesion induced by BMY-25282, however, were not detectably increased in EMT6 cells exposed to this agent in the presence of DETC in spite of the large increase in cytotoxicity under these treatment conditions. No single strand breaks were detected in cells exposed to either BMY-25282 or BMY-25282 plus DETC. The findings support the concept that oxygen radicals may have a role in the aerobic cytotoxicity of some of the mitomycin antibiotics, and that the lesions responsible for cytotoxicity produced by oxygen radicals may not reside entirely at the level of DNA.     

Neurogenic inflammation, vascular permeability, and mast cells. II. Additional evidence indicating that mast cells are not involved in neurogenic inflammation.

Activation of cutaneous sensory nerves induces vasodilatation and vascular permeability, i.e., neurogenic inflammation. We examined the histology and possible mast cell involvement in cutaneous neurogenic inflammation induced by electrical nerve stimulation (ENS). Three lines of evidence indicated that mast cells were not involved in rodent cutaneous neurogenic inflammation induced by electrical stimulation of the saphenous nerve. 1) Most mast cells (86.5% of all mast cells in the dorsal skin of the paw) were found in the deep dermis, whereas vessels developing increased vascular permeability after nerve stimulation (visualized with the supravital dye Monastral blue B, a macro-molecular tracer) were localized predominantly in the superficial dermis. By contrast, i.v. substance P, which also causes increased cutaneous vascular permeability, predominantly caused deeper vessels to leak. As analyzed by electron microscopy, the vessels that developed permeability in response to nerve stimulation, and were thereby stained with Monastral blue B, were found to be exclusively postcapillary venules. 2) Disodium cromoglycate (DSCG), a mast cell stabilizing compound, inhibited the cutaneous vascular permeability induced by intradermal injections of anti-IgE in a dose-dependent manner. By contrast, vascular permeability induced by ENS was not influenced by disodium cromoglycate treatment. 3) ENS and i.v. substance P both induced cutaneous vascular permeability in mast cell-deficient W/Wv mice, despite the fact that their skin contained only 4.7% of the mast cells present in their normal +/+ litter mates. The magnitude of ENS-induced vascular permeability responses in W/Wv mice were similar to control +/+ and BALB/c mice. This study supports our earlier observations suggesting that mast cell activation is not essential for the initial, vascular permeability phase of neurogenic inflammation in rodent skin.     

Effects of isoproterenol treatment for 7 days on inflammatory mediators in the rat aorta

The aim of the present study was to evaluate the effect of overstimulation of beta-adrenoceptors on vascular inflammatory mediators. Wistar rats were treated with the beta-adrenoceptor agonist isoproterenol (0.3 mg.kg(-1).day(-1) sc) or vehicle (control) for 7 days. At the end of treatment, the right carotid artery was catheterized for arterial and left ventricular (LV) hemodynamic evaluation. Isoproterenol treatment increased LV weight but did not change hemodynamic parameters. Aortic mRNA and protein expression were quantified by real-time RT-PCR and Western blot analysis, respectively. Isoproterenol enhanced aortic mRNA and protein expression of IL-1beta (124% and 125%) and IL-6 (231% and 40%) compared with controls but did not change TNF-alpha expression. The nuclear-to-cytoplasmatic protein expression ration of the NF-kappaB p65 subunit was increased by isoproterenol treatment (51%); in addition, it reduced the cytoplasmatic expression of IkappaB-alpha (52%) in aortas. An electrophoretic mobility shift assay was performed using the aorta, and increased NF-kappaB DNA binding (31%) was observed in isoproterenol-treated rats compared with controls (P < 0.05). Isoproterenol treatment increased phenylephrine-induced contraction in aortic rigs (P < 0.05), which was significantly reduced by superoxide dismutase (150 U/ml) and sodium salicylate (5 mM). Cotreatment with thalidomide (150 mg.kg(-1).day(-1) for 7 days) also reduced hyperreactivity to phenylephrine induced by isoproterenol. In conclusion, overstimulation of beta-adrenoceptors increased proinflammatory cytokines and upregulated NF-kappaB in the rat aorta. Moreover, local oxidative stress and the proinflammatory state seem to play key roles in the altered vascular reactivity of the rat aorta induced by chronic beta-adrenergic stimulation.     

Role of the protease in the permeability enhancement by Vibrio vulnificus

The protease produced by Vibrio vulnificus enhances vascular permeability through histamine release from mast cells and activation of the plasma kallikrein-kinin system which generates bradykinin when injected into the dorsal skin. V. vulnificus living cells also enhanced vascular permeability within a few hours after the injection into the dorsal skin. The permeability-enhancing activity of living cells was greatly reduced by addition of soybean trypsin inhibitor, a specific inhibitor for plasma kallikrein-kinin system, or anti-protease IgG. Two protease-deficient mutants induced by nitrosoguanidine treatment had only one-tenth permeability-enhancing activity of a wild-type strain. These results indicate that V. vulnificus elaborates the protease in vivo and that the protease elaborated enhances vascular permeability through release of chemical mediators such as histamine and bradykinin and forms edema.     

Paracrine VEGF/VE-cadherin action on ovarian cancer permeability

Ascites formation associated with neoplasms is most likely due to increased vascular permeability, a process in which vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) plays a pivotal role. We hypothesized that tumor-derived VEGF/VPF modulates ascites formation through a paracrine effect on both tumor and peritoneal vessels. We investigated human vascular endothelial permeability using a newly developed dual-chamber permeability assay by co-culturing human umbilical vein cells with and without ovarian cancer cell lines (OVCAR-3, Hey-A8, and OCC-1) in the presence or absence of a human VEGF monoclonal antibody and VE-cadherin function-blocking antibody. This method permits determination of mechanisms by which substances released from neoplasms and other sources of vascular endothelial cell secretagogues modulate vascular permeability and likely other pathologic states.     

Pharmacologic agents for the in vivo detection of vascular sodium transport defects in hypertension

Anatagonists to angiotensin, catecholamines, aldosterone, and vasopressin have long been used to help determine agonist roles in hypertension. We here call attention to a possible extension of this approach to detect, evaluate, and treat vascular sodium transport defects in hypertension. Two basic types of transport defects have been identified in the blood vessels of hypertensive animals, increased sodium permeability and decreased sodium pump activity. Intravenous injection of 6-iodo-amiloride, a sodium channel blocker and vasodilator, produces an immediate and sustained decrease in blood pressure in two genetic models of hypertension characterized by increased permeability of the vascular smooth muscle cell membrane to sodium (Okamoto spontaneously hypertensive rat, Dahl salt sensitive rat), whereas it produces only a transient fall in arterial pressure in two renal models of hypertension having normal sodium permeability in vascular smooth muscle cells (reduced renal mass-saline rat, one-kidney, one clip rat). Canrenone, a metabolic product of spironolactone which can compete with oubain for binding to Na+,K+-ATPase at the digitalis receptor site, decreases blood pressure in a low renin, volume expanded model of hypertension which has been shown to have depressed sodium pump activity in arteries and increased sodium pump inhibitor in plasma (reduced renal mass-saline rat) but has no effect on blood pressure in a genetic model of hypertension which has been shown to have increased sodium pump activity secondary to increased sodium permeability (spontaneously hypertensive rat). Thus, a sodium channel blocker and a competitor to ouabain binding can detect and determine the functional significance of sodium transport defects in the blood vessels of intact hypertensive animals. Studies in red and white blood cells suggest that similar defects may exist in the blood vessels of hypertensive humans. Thus, this approach, probing for vascular transport defects in the intact animal, may ultimately also be useful in the clinical setting.     

Selective inhibition of cholesterol synthesis in liver versus extrahepatic tissues by HMG-CoA reductase inhibitors

Hepatic specificity of inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase may be achieved by efficient first-pass liver extraction resulting in low circulating drug levels, as with lovastatin, or by lower cellular uptake in peripheral tissues, seen with pravastatin. BMY-21950 and its lactone form BMY-22089, new synthetic inhibitors of HMG-CoA reductase, were compared with the major reference agent lovastatin and with the synthetic inhibitor fluindostatin in several in vitro and in vivo models of potency and tissue selectivity. The kinetic mechanism and the potency of BMY-21950 as a competitive inhibitor of isolated HMG-CoA reductase were comparable to the reference agents. The inhibitory potency (cholesterol synthesis assayed by 3H2O or [14C]acetate incorporation) of BMY-21950 in rat hepatocytes (IC50 = 21 nM) and dog liver slices (IC50 = 23 nM) equalled or exceeded the potencies of the reference agents. Hepatic cholesterol synthesis in vivo in rats was effectively inhibited by BMY-21950 and its lactone form BMY-22089 (ED50 = 0.1 mg/kg p.o.), but oral doses (20 mg/kg) that suppressed liver synthesis by 83-95% inhibited sterol synthesis by only 17-24% in the ileum. In contrast, equivalent doses of lovastatin markedly inhibited cholesterol synthesis in both organs. In tissue slices from rat ileum, cell dispersions from testes, adrenal, and spleen, and in bovine ocular lens epithelial cells, BMY-21950 inhibited sterol synthesis weakly in vitro with IC50 values 76- and 188-times higher than in hepatocytes; similar effects were seen for BMY-22089. However, the IC50 ratios (tissue/hepatocyte) for lovastatin and fluindostatin were near unity in these models. Thus, BMY-21950 and BMY-22089 are the first potent synthetic HMG-CoA reductase inhibitors that possess a very high degree of liver selectivity based upon differential inhibition sensitivities in tissues. This cellular uptake-based property of hepatic specificity of BMY-21950 and BMY-22089, also manifest in pravastatin, is biochemically distinct from the pharmacodynamic-based disposition of lovastatin, which along with fluindostatin exhibited potent inhibition in all tissues that were exposed to it.     

Acute exposure to a moderate strength static magnetic field reduces edema formation in rats

External application of static magnetic fields (SMF), used specifically for the treatment of inflammatory conditions such as soft tissue injuries, has recently become popular as a complementary and/or alternative therapy with minimal investigation into efficacy or mechanism. Localized inflammation was induced via injection of inflammatory agents lambda-carrageenan (CA) or histamine into rat hindpaws, alone or in conjunction with pharmacological agents, resulting in a spatially and temporally defined inflammatory reaction. Application of a 10- or 70-mT, but not a 400-mT, SMF for 15 or 30 min immediately following histamine-induced edema resulted in a significant, 20-50% reduction in edema formation. In addition, a 2-h, 70-mT field application to CA-induced edema also resulted in significant (33-37%) edema reduction. Field application before injection or at the time of maximal edema did not influence edema formation or resolution, respectively. Together, these results suggest the existence of a therapeutic threshold of SMF strength (below 400 mT) and a temporal dependence of efficacy. Administration of pharmacological agents directed at nitric oxide signaling and L-type Ca(2+) channel dynamics in conjunction with SMF treatment and histamine-induced edema revealed that the potential mechanism of SMF action may be via modulation of vascular tone through effects on L-type Ca(2+) channels in vascular smooth muscle cells.     

Trophic effects induced by alpha1D-adrenoceptors on endothelial cells are potentiated by hypoxia

Catecholamines have been shown to be involved in vascular remodeling through the stimulation of alpha(1)-adrenoceptors (alpha(1)-ARs). Recently, it has been demonstrated that catecholamines can stimulate angiogenesis in pathological conditions, even if the mechanisms and the AR subtypes involved still remain unclear. We investigated the influence of hypoxia (3% O(2)) on the ability of picomolar concentrations of phenylephrine (PHE), which are unable to induce any vascular contraction, to induce a trophic effect in human endothelial cells through stimulation of the alpha(1D)-subtype ARs. PHE, at picomolar concentrations, significantly promoted pseudocapillary formation from fragments of human mature vessels in vitro. Exposure to hypoxia significantly potentiated this effect, which was inhibited by the selective alpha(1D)-AR antagonist BMY-7378 and by the nitric oxide synthase inhibitor L-NAME, suggesting that alpha(1D)-ARs were involved in this effect through activation of the nitric oxide pathway. Proliferation and migration of HUVEC were also affected by picomolar PHE concentrations. Again, these effects were significantly potentiated in cells exposed to hypoxia and were inhibited by BMY-7378 and by N(G)-nitro-L-arginine methyl ester. Conversely, the alpha(1A)-AR-selective antagonist (S)-(+)-niguldipine hydrochloride and the alpha(1B)-AR antagonist chloroethylclonidine dihydrochloride did not modify endothelial cell migration and proliferation in response to PHE. These results demonstrate that the stimulation of alpha(1D)-ARs, triggered by picomolar PHE concentrations devoid of any contractile vascular effects, induces a proangiogenic phenotype in human endothelial cells that is enhanced in a hypoxic environment. The role of alpha(1D)-ARs may become more prominent in the adaptive responses to hypoxic vasculature injury.     

Hydraulic conductance of lung endothelial phenotypes and Starling safety factors against edema

Recent permeability studies comparing endothelial cell phenotypes derived from alveolar and extra-alveolar vessels have significant implications for interpreting the mechanisms of fluid homeostasis in the intact lung. These studies indicate that confluent monolayers of rat pulmonary microvascular endothelial cells had a hydraulic conductance (L(p)) that was only 5% and a transendothelial flux rate for 72-kDa dextran only 9% of values determined for rat pulmonary artery endothelial cell monolayers. On the basis of previous studies partitioning the filtration coefficients between alveolar and extra-alveolar vascular segments in rat lungs and previous studies of lymph albumin fluxes and permeability, the contribution of the alveolar capillary segment to total albumin flux in lymph was estimated to be less than 10%. In addition, the Starling safety factors against the edema calculated for the alveolar capillaries are quite different from those estimated for whole lung. Estimates of the edema safety factor due to increased filtration across the alveolar capillary wall based on the low L(p) indicate it is quantitatively the greatest safety factor, although it would be a minor safety factor for extra-alveolar vessels. Also, a markedly higher effective protein osmotic absorptive force for plasma proteins must occur in the capillaries relative to extra-alveolar vessels. The lower L(p) for alveolar capillaries also has implications for the sequence of hydrostatic edema formation, and it also may have a role in preventing exercise-induced alveolar flooding.