Amelioration of renal ischemic injury by phosphocreatine

Phosphocreatine (PCr) is a critical intracellular energy reservoir used in the regeneration of ATP. The aim of this study was to determine the efficacy of exogenously added PCr on preservation of renal function in an in vitro model. The renal artery and ureter of a rat were cannulated and the kidney was subjected to 45 min of normothermic in vivo ischemia. The kidneys were then perfused ex vivo with either a Krebs-bicarbonate solution (Krebs) or a Krebs solution containing 3 mM PCr or an osmotically balanced solution containing 3 mM PCr. Our results indicate that the perfusion of kidneys subjected to 45 min of warm ischemia with solutions containing PCr resulted in significant improvements in GFR, RPF, and V, FRNa and FRH2O compared to KREBS alone. This suggests that the important factor in preservation of kidney function after an initial ischemic insult may be the addition of PCr rather that the electrolyte solution used.

Stimulation of endothelial secretion of tissue-type plasminogen activator by repetitive stretch

Endothelial cells (EC) synthesize many of the fibrinolytic components and anticoagulants present in plasma. EC have been demonstrated to release tissue type plasminogen activator (t-PA) and its rapid inhibitor type 1 plasminogen activator inhibitor (PAI-1). In vivo, EC lining a blood vessel are exposed to the forces of the circulation, predominantly shear stress and pulsatile stretch. We have previously reported that repetitive stretch of EC in culture will stimulate prostacyclin secretion. In this study, the effects of cyclic stretch on the production of t-PA and PAI-1 by cultured EC were examined. EC harvested from human saphenous vein were seeded in culture plates with flexible membrane bottoms and grown to confluence. Vacuum (-20 kPa) was used to deform the membrane bottoms to 24% maximum strain. EC in the experimental group were subjected to 24% maximum strain at 60 cycles/min (0.5 sec elongation alternating with 0.5 sec relaxation), while control EC were grown on the same membranes but kept stationary in the same incubator. After 1, 3, and 5 days, the cell numbers were counted and the media were collected and analyzed for t-PA and PAI-1 by ELISA. The result shows a significant increase in t-PA production with the cyclic stretch on Days 3 and 5. There was no significant difference in PAI-1 levels in stretched versus stationary EC. We concluded that cyclic stretch of EC in vitro can selectively stimulate t-PA production and may account for the relative nonthrombogenicity of the endothelium in vivo.

Design and evaluation of a fiberoptic fluorescence guided laser recanalization system

Current angioplasty techniques for recanalization of totally occluded arteries are limited by the inability to cross the occlusion and by the risk of perforation. A fiberoptic fluorescence guided laser recanalization system was developed and evaluated in vitro for recanalization of 17 human femoral or tibial totally occluded arterial segments (length 1.9-6.8 cm, diameter 2.5-6.0 mm). A 400 or 600 micron silica fiber was coupled to a helium-cadmium laser (lambda = 325 nm) for fluorescence excitation and to a holmium: YAG laser (lambda = 2.1 micron) for tissue ablation. Fluorescence was recorded during recanalization after every other holmium laser pulse. During recanalization, each arterial segment was bent 30-90 degrees with respect to the fiber to simulate arterial tortuosity. Ablation continued with fiber advancement as long as the fluorescence confirmed that the target tissue was atherosclerotic. Arterial spectra were classified as normal or atherosclerotic by an on-line computerized fluorescence classification algorithm (sensitivity 93%, specificity 95%). Normal fluorescence necessitated redirection of the fiber greater than 30 times per segment to continue recanalization. Fifteen of 17 totally occluded arteries had multiple recanalization channels created following total energy delivery of 40-1,016 Joules per segment with no angiographic or histologic evidence of laser perforation. Two heavily calcified arterial occlusions were not recanalized due to inhibition of holmium: YAG laser ablation by the recording of normal fluorescence spectra. Therefore, this fluorescence guided laser recanalization system appears safe and effective for recanalization of totally occluded arteries and merits in vivo evaluation. However, the lower sensitivity of fluorescence detection of heavily calcified plaques may limit the efficacy (but not safety) of fluorescence guided recanalization of heavily calcified occlusions.

Stimulation of adenylate cyclase activity in cultured endothelial cells subjected to cyclic stretch

While vascular endothelial cells are repeatedly stretched by the pulsatile nature of cardiac output, in vitro models traditionally used to study vascular biology involve static culture techniques. We have recently shown that pulsatile stretching of endothelial cells in culture will increase their rates of proliferation and regulate their secretion of macromolecules. The aim of this study was to determine whether membrane adenylate cyclase is involved in intracellular signalling during pulsatile stress. Bovine aortic endothelial cells were seeded on flexible-bottomed culture wells (3 x 10(5) cells/25 mm well) and allowed to attach for 48 hours. The culture wells were placed in a vacuum-operated stress providing instrument and subjected to 0.5 s of 24% strain, 0.5 s relaxation (60 cycles/min) for 0, 1, 3, 5, 7, 10 and 15 minutes (N = 24 wells/time point). Cells were homogenized and a crude membrane preparation (27,000 x g) was assayed for adenylate cyclase under basal and forskolin (100 microM) stimulated conditions. The results indicate that there is a time-dependent increase in both basal and stimulated adenylate cyclase with cyclic deformation and suggest that there may be a "stretch receptor" coupled to adenylate cyclase which can modulate endothelial cell function with hemodynamic changes.

Enhanced production of endothelium-derived contracting factor by endothelial cells subjected to pulsatile stretch

The purpose of this study was to assess the role of cyclic deformation in modulating the production by endothelial cells (ECs) in culture of a recently described endothelium-derived smooth muscle cell contracting factor, endothelin. We grew bovine aortic ECs to confluence on culture plates with flexible membrane bottoms. Vacuum (-20 kPa) was applied to deform the membrane to 24% strain at 60 cycles/min for 1, 3, or 5 days. Control ECs were grown on the same membrane but without vacuum deformation. The conditioned media were collected, centrifuged at 10,000 rpm for 10 minutes to remove cells and debris, and the supernatant fluid was subjected to radioimmunoassay for endothelin. The results demonstrate that bovine aortic ECs release a basal level of endothelin under stationary conditions (107.1 +/- 14.7 pg/10(5) cells), and this production increased fivefold to sixfold with cyclic stretch. Thus physical forces exerted on ECs in culture can influence the secretion of this vasoconstrictive molecule.

Modulation of endothelial cell phenotype by cyclic stretch: inhibition of collagen production

Endothelial cells (EC) are constantly subjected to pulsatile stretch in vivo, but most studies of EC are performed under stationary tissue culture conditions. The aim of this study was to examine the effect of repetitive mechanical stretching on EC collagen production. Bovine EC were seeded in 35-mm flexible-bottom culture wells, allowed to attach for 24 hr, and then subjected to up to 24% elongation cyclic deformation, 3 cycles/min, 10 sec of elongation alternating with 10 sec of relaxation, for 5 days. Twenty-four hours prior to harvesting, serum-free media containing 50 microCi [3H]proline (PRO), an amino acid hydroxylated (OH) in collagen, and 50 micrograms/ml ascorbate were added per well. On Days 1, 3, and 5, the media and cells were collected, precipitated with TCA, sedimented, lyophilized, and analyzed by HPLC for OH-PRO and PRO. The results of this study indicate that EC production of collagen is inhibited with repetitive deformation. Since previous studies have shown that EC proliferation is increased after 3 cycles/min stretching, this supports the theory that collagen gene expression varies inversely with the proliferative state.

The influence of perfusate viscosity, RBC deformability and drag on the function of an isolated perfused rat kidney

There is increasing clinical interest in improving blood rheology to optimize organ function, but studies correlating the two are scarce. To study this, rat kidneys were perfused in vitro at 37 degrees C at a constant mean renal arterial pressure of 160 mm Hg. The perfusate consisted of an oxygenated Krebs HCO3 buffer containing 1 mg/ml glucose, 0.5 mg/ml creatinine, amino acids, [3H]inulin (marker for GFR), 2.5 g/dl albumin, and 10 or 20% hematocrit. In some experiments, RBC were made nondeformable by heating at 50 degrees C for 20 min. Deformability was measured by an ektacytometer. In other experiments, 0.001% of an anionic polyacrylamide (Separan), a drag-reducing agent, was added to the perfusate. Viscosity was measured with a cone and plate viscometer, [Na+] with a flame spectrophotometer, and perfusate flow with a Brooks in-line flowmeter. Other functional parameters, GFR, urine flow, RPF, and reabsorption of sodium and water, were also measured. The results indicate that (1) making RBC nondeformable or increasing viscosity by increasing hematocrit reduces renal function, and (2) addition of a drag-reducing agent improves renal function at 20% hematocrit. We conclude that rheologic manipulation of a perfusate solution can alter flow and renal function.

Enhanced collagen production by smooth muscle cells during repetitive mechanical stretching

We examined the effect of repetitive mechanical stretching on smooth muscle cell (SMC) collagen production. Porcine SMCs from passages 3 through 7 were seeded in 35-mm2 flexible-bottomed culture wells at a concentration of 2 x 10(5) cells per well and allowed to attach for 24 hours. The experimental group was placed in a vacuum-operated stress-providing instrument that exerted an average elongation of 25% at maximum downward deflection of the culture plate bottom. The stretched cells (nine wells per day) were subjected to a cyclic force regimen of 10 s of elongation and 10 s of relaxation for five days. The control cells (nine wells per day) were subjected to incubation conditions similar to those in the experimental group but without cyclic stretching. Twenty-four hours before harvesting, serum-free medium containing 50-microCi tritiated proline, an amino acid hydroxylated in collagen (hydroxyproline), and 50 micrograms/mL of ascorbate was added per well. On days 3 and 5 the medium and cells were collected, precipitated with trichloroacetic acid, and then sedimented, lyophilized, and analyzed to separate hydroxyproline and proline. Values for collagen and noncollagen protein were calculated after quantitation of the hydroxyproline and proline concentrations. The results indicate that three-cycle-per-minute stretching coordinately stimulated SMC production of collagen and noncollagen protein. We conclude that pulsatile stretch enhances collagen and noncollagen protein synthesis.

Prostacyclin synthetic activity in cultured aortic endothelial cells undergoing cyclic mechanical deformation

The effect of mechanical stretching on prostacyclin (PGI2) synthesis was studied by growing bovine aortic endothelial cells on flexible-bottomed culture plates that could be deformed by vacuum. A stress unit was used to exert an elongation of 24% at maximum downward deflection of the culture plate bottom. The experimental group was subjected to cycles of 10 seconds of elongation, 10 seconds of relaxation for 1, 3, or 5 days. The control group was subjected to similar incubations but without cyclic stretch. Twenty-four hours before collection, the medium was replaced with new medium that was devoid of serum. On days 1, 3, and 5, the 24-hour culture medium was collected (basal state). Arachidonic acid (20 mumol/L) was then added to each culture and incubated for 5 minutes at 37 degrees C. The medium was then collected to assess prostacyclin synthetic activity (stimulated state). Media were assayed for PGI2 and thromboxane A2 by radioimmunoassays for 6-keto-PGF1 alpha and thromboxane B2, the respective stable hydrolysis product. The results indicate that cyclic stretching, while not altering the basal production of PGI2, increases PGI2 synthetic capacity in a time-dependent manner. These data suggest that it may be inappropriate to extrapolate the mechanisms of in vivo PGI2 release from studies of endothelial cells in stationary culture.

Osteoblasts increase their rate of division and align in response to cyclic, mechanical tension in vitro

Bone adapts to physical deformation in vivo, yet the mechanism of the adaptive process remains unknown. One reason for this perplexity has been the difficulty in examining the effects of a well-defined deformation regimen on individual bone cells. With the utilization of novel, flexible-bottomed cell culture plates, one can study the effects of cyclic strain on the morphologic and biochemical adaptations of individual osteoblasts in vitro. Avian, calvarial osteoblast-like cells, from passes 2-5, responded to cyclic strain, by increasing their rates of DNA synthesis and cell division during the first 72 h after initiation of a continuous deformation regimen comprised of 3 cycles per min of 0-24% elongation. In addition, within hours after initiation of the deformation regimen, cells oriented 90 degrees to the applied strain field at the periphery of the culture plate in the region of maximum strain and elongation.

Response of porcine aortic smooth muscle cells to cyclic tensional deformation in culture

The vascular wall is continuously subjected to pulsatile hydrostatic pressures. However, most studies of smooth muscle cells (SMC) are done under static tissue culture conditions. We have utilized a flexible-bottom culture plate and applied cyclic tensional deformation to cultured SMC. Recent studies have shown that endothelial cells (EC) proliferate but remain randomly oriented when subjected to a force regimen of 3 cycle/min of up to 24% elongation. The current experiments were performed to study the effects of a similar force regimen on SMC. Porcine SMC were seeded at 200,000 cells/35-mm2 well and permitted to adhere for 24 hr. After 24 hr, the plates were placed on a vacuum-operated stress-providing unit that exerted a 24% elongation on the culture plate substratum at maximum downward deflection of the plate bottom. The stretched cells (n = 6 wells/day) were subjected to cycles of 10 sec of 24% elongation and 10 sec of relaxation for 7 days. The control cells (n = 6 wells/day) were subjected to similar incubations as the control group but without cyclic deformation. Media were changed every 24 hr. [3H]Thymidine (THY), a precursor for DNA synthesis, was added (2 microCi/well) to plates 24 hr prior to harvesting. On Days 0, 1, 3, 5, and 7 cells were counted and analyzed for THY incorporation. While previous results indicate that pulsatile stretching stimulates EC, the present study indicates that a similar regimen of stress inhibits SMC proliferation. THY incorporation into SMC paralleled the observed changes in cell count. Morphologically, SMC aligned in an annular pattern in response to applied strain, whereas EC maintained a random orientation.(ABSTRACT TRUNCATED AT 250 WORDS)

Variceal bleeding, hypersplenism, and systemic mastocytosis. Pathophysiology and management

Systemic mastocytosis is characterized by an abnormal proliferation of tissue mast cells. Though rarely a surgical disease, it occasionally presents as variceal bleeding secondary to portal hypertension. Ultrastructural studies of the liver and spleen and portal pressure measurements support the hypothesis that a perisinusoidal intrahepatic fibrosis is responsible for the increased portal pressure. When variceal bleeding complicates systemic mastocytosis, shunt surgery is indicated, with the type of shunt dictated by both hematologic and hemodynamic issues. Satisfactory blockade of histamine release can be achieved preoperatively by disodium cromoglycate and/or histamine antagonists to obviate any systemic effects precipitated by shunting of mast cell-rich splenic blood into the systemic circulation.

Alterations in aortic endothelial cell morphology and cytoskeletal protein synthesis during cyclic tensional deformation

Previous studies have shown that bovine aortic endothelial cells (ECs) in culture respond to repetitive tensional deformation with an increase in deoxyribonucleic acid synthesis and cell proliferation. This study was designed to determine whether cyclic tensional deformation of ECs in vitro induces different morphologic or protein synthetic responses. ECs from passages 6 through 9 were seeded in 35 mm2 well silicone rubber plates at 2 x 10(5) cells/well and allowed to attach for 24 hours. The experimental group was placed in a vacuum-operated stress-providing device that exerted an elongation of 24% at maximum downward deflection of the culture plate bottom and was subjected to repetitive cycles of 10 seconds of 24% maximum elongation and 10 seconds of relaxation for 5 days. The control group was subjected to similar incubation conditions but without stretch. 35S-methionine (500 muCi/well) was added to the plates 24 hours before harvesting, and two-dimensional gels of the harvested lysates (isoelectric focusing with pH 3 to 10 ampholytes followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis on 12.5% gels) were performed and the labeled proteins visualized by autoradiography. The data indicate that there is a differential synthesis of proteins, with synthesis of some proteins decreased or ablated whereas other proteins were increased in response to cyclic mechanical tension. The actin filament organization was evaluated after staining with rhodamine phalloidin, a fluorescent F-actin probe. The ECs subjected to tension had a more polygonal shape and demonstrated pseudopods and actin stress fibers, whereas ECs cultured under static conditions were more rounded and did not express actin stress cables.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleviation of cyclosporine nephrotoxicity with verapamil and ATP-MgCl2. Mitochondrial respiratory and calcium studies

Although recent studies have shown that combined treatment with verapamil and ATP-MgCl2 (ATP) prevents cyclosporine (CyA)-induced nephrotoxicity, the mechanism of these effects remains unknown. To study this, rat kidneys were perfused at 100 mmHg for 100 minutes with Krebs buffer containing 7.5 g/dL of albumin and substrates. After an equilibration period of 30 minutes, 500 ng/mL CyA was added. In some experiments 1 microgram/mL verapamil was added 10 minutes prior to CyA and in others 2 mM ATP was added to CyA. At the end of the perfusion, cortical mitochondria (mito) were isolated and mito Ca2+ and Mg2+ (mumoles/g protein) and respiratory control ratios (RCR) were measured. In addition, total tissue Ca2+ and Mg2+ levels were measured. The results indicate that CyA treatment leads to an accumulation of mito Ca2+ and a decrease in ADP/O ratio. Simultaneous administration of ATP with CyA led to an increased mito Ca2+ accumulation and depressed RCR, which were corrected by verapamil pretreatment. The combination of verapamil pretreatment and ATP cotreatment with CyA increased tissue ATP levels from 0.8 +/- 0.4 (control) to 1.4 +/- 0.1 mumol/g. This pharmacologic regimen may prevent CyA-induced nephrotoxicity by preventing mito Ca2+ accumulation and by preserving mitochondrial respiratory function. This allows a more efficient generation of ATP and consequently preservation of renal function.

Aortic thrombosis with paraplegia: an unusual consequence of blunt abdominal trauma

Aortic thrombosis occurring after blunt abdominal trauma is a rare but recognized event. Most of these patients present with progressive and profound neurologic compromise. Successful management requires early diagnosis, maintenance of hemodynamic stability, and prompt revascularization. Despite appropriate management a large percentage of these patients (unprotected by heparin or collateral vessels) will remain paraplegic.

Mechanical stress stimulates aortic endothelial cells to proliferate

The effects of applied cyclic tensional deformation and relaxation on cultured bovine aortic endothelial cells were examined. Endothelial cells from passages 3 to 9 were seeded in flexible-bottomed plates and allowed to attach for 24 hours. Endothelial cells in the experimental group (n = 6 wells per time point) were placed in a vacuum-operated stress-providing instrument that exerted an average elongation of 10% at maximum downward deflection of the culture plate bottom. The stretched endothelial cells were subjected to repeating cycles of 10 seconds elongation and 10 seconds relaxation from days 1 through 7 in culture. Endothelial cells in the control group (n = 6 wells per time point) were subjected to similar incubation conditions as the experimental group but without tensional deformation. Tritiated thymidine was added to cells 24 hours before harvesting. On days 0, 1, 3, 5, and 7 cells were counted and analyzed for trichloroacetic acid-precipitable tritiated thymidine incorporation. The results showed that 3 cycles/min mechanical stretching stimulated deoxyribonucleic acid synthesis and endothelial cell division. We conclude that cyclic tensional deformation may stimulate endothelial cell proliferation. It is possible that naturally occurring cyclic mechanical deformation in vivo, such as the repetitive stretching and relaxation of aortic tissue by the heart, may invoke a particular pattern of synthesis and division in endothelial cells.