Lisa M. Wilson

Environmental Stress Causes Mast Cell Degranulation, Endothelial and Epithelial Changes, and Edema in the Rat Intestinal Mucosa

Objective: Mental stress has been shown to produce intestinal disease, but the effects of a mild environmental stress on intestinal physiology have not been elucidated. This study was performed to determine the effects of environmental stress on the ultrastructure of the intestinal mucosa, using the rat as an experimental model.

Effect of pressure on aortic hydraulic conductance.

This study was performed to determine whether the transmural hydraulic conductance (Lp) of the rabbit aortic wall depends on its distension. In 19 rabbits, the aorta was cannulated in situ and perfused at a given pressure with a physiologically buffered solution containing 4% bovine serum albumin. The output cannula was then occluded to limit fluid flow to that traversing the artery wall. External diameter and transmural fluid flow were measured at three pressures (eight rabbits, group 1) or at four pressures (12 rabbits, group 2) in each vessel. Transmural fluid flow was determined by monitoring the velocity of an air bubble within a buffer-filled tube leading to the input cannula. From group 1 measurements, Lp values (mean +/- SD) at 50, 100, and 150 mm Hg were calculated to be 3.8 +/- 2.8, 3.5 +/- 1.3, and 4.1 +/- 1.2 x 10(-8) cm/sec/mm Hg, respectively. Group 2 measurements gave values of 4.2 +/- 1.6, 3.8 +/- 1.1, 3.8 +/- 1.1, and 4.2 +/- 1.1 x 10(-8) cm/sec/mm Hg at 75, 100, 125, and 150 mm Hg, respectively. Paired Students t tests indicated no significant change in Lp with pressure. However, linear regression analysis demonstrated a weak correlation between Lp values obtained at 50 and 100 mm Hg (r2 = 0.30) and at 75 and 100 mm Hg (r2 = 0.36). Values of Lp at 100 and 150 mm Hg and at 125 and 150 mm Hg were closely correlated in each case. These results suggest that between 50 and 100 mm Hg the structural properties of the aortic wall change so as to alter Lp but not in the same way in each vessel. Lp may increase or decrease depending on which structural change predominates in a particular vessel.

Effect of Atherosclerosis on Transmural Convection and Arterial Ultrastructure Implications for Local Intravascular Drug Delivery

Local infusion of agents through perforated catheters may reduce neointimal formation following vascular angioplasty. Such treatment will succeed only if the drug is retained within the arterial intima long enough to promote repair. Drugs will be dispersed throughout the wall predominantly by transmural convection instead of diffusion if the Peclet number, Pe = J (1-delta f)/P, is greater than unity, where J is the transmural fluid flow per unit surface area and delta(f) and P are the reflection and permeability coefficients to the drug, respectively. Although the targets of local drug delivery will be atherosclerotic vessels, little is known about the transport properties of these vessels. Accordingly, we evaluated the effects of hypercholesterolemia and atherosclerosis on J per unit pressure (hydraulic conductance, Lp) and on ultrastructure in femoral arteries. Measurements were made at 30, 60, and 90 mm Hg in anesthetized New Zealand white rabbits fed a normal diet (n = 6) and after 3 weeks of lipid feeding (n = 19). Atherosclerosis was induced in six lipid-fed animals by air desiccation of a femoral artery. Hydraulic conductance was significantly greater in vessels from hypercholesterolemic than from normal animals and decreased with pressure only in hypercholesterolemic arteries. Atherosclerosis did not augment hydraulic conductance compared with hypercholesterolemia alone. Electron microscopic examination demonstrated damaged endothelium in hypercholesterolemic arteries and both altered endothelium and less tightly packed medial tissue, compared with controls, in atherosclerotic vessels, at least at lower pressures. Peclet numbers for macromolecules exceeded unity for all three groups of arteries and reached 0.3 to 0.4 for molecules as small as heparin. Thus, convection plays a dominant role in the distribution of macromolecular agents following local delivery and may result in their rapid transport to the adventitia in the femoral artery.

Ultrastructural effects of intravascularly injected polyethylene glycol-hemoglobin in intestinal mucosa.

Polyethylene glycol (PEG)-conjugated Hb (PEG-Hb) is being considered as a blood substitute. Previously, we showed that PEG-Hb extravasates rapidly from the intestinal mucosa and causes transient epithelial sloughing, resulting in temporary unimpeded passage of material between the intestinal lumen and the microcirculation. The present study quantifies the time course of factors related to this disturbance. Anesthetized Sprague-Dawley rats (350-450 g) were injected with a bolus of PEG-Hb (10 mg/ml) in saline. Control animals received saline, alone or with Dextran 70 (5 mg/ml). After 2, 8, 15, 60, or 90 min, the small intestine was perfusion fixed for microscopy (4 animals for each time point). Epithelial cell detachment and mucosal mast cell degranulation peaked at 2 and 8-15 min, respectively, but by 90 min were back to normal. Goblet cell secretion increased with time up to 8-15 min, after which it leveled off. Mean interstitial width was significantly greater 8 min after injection than for controls and continued to increase with time. In capillaries, endothelial fenestral diaphragms were replaced by thick, amorphous structures. Mesenteric mast cell degranulation was significantly greater 60-90 min after injection compared with controls. We propose that these results are consistent with intravascular injection of PEG-Hb invoking a transient inflammatory response in the intestine.Polyethylene glycol (PEG)-conjugated Hb (PEG-Hb) is being considered as a blood substitute. Previously, we showed that PEG-Hb extravasates rapidly from the intestinal mucosa and causes transient epithelial sloughing, resulting in temporary unimpeded passage of material between the intestinal lumen and the microcirculation. The present study quantifies the time course of factors related to this disturbance. Anesthetized Sprague-Dawley rats (350-450 g) were injected with a bolus of PEG-Hb (10 mg/ml) in saline. Control animals received saline, alone or with Dextran 70 (5 mg/ml). After 2, 8, 15, 60, or 90 min, the small intestine was perfusion fixed for microscopy (4 animals for each time point). Epithelial cell detachment and mucosal mast cell degranulation peaked at 2 and 8-15 min, respectively, but by 90 min were back to normal. Goblet cell secretion increased with time up to 8-15 min, after which it leveled off. Mean interstitial width was significantly greater 8 min after injection than for controls and continued to increase with time. In capillaries, endothelial fenestral diaphragms were replaced by thick, amorphous structures. Mesenteric mast cell degranulation was significantly greater 60-90 min after injection compared with controls. We propose that these results are consistent with intravascular injection of PEG-Hb invoking a transient inflammatory response in the intestine.

Effects of Environmental Stress on the Architecture and Permeability of the Rat Mesenteric Microvasculature

Objective: This study was performed to determine the effects of environmental stress on the leakage to albumin and architecture of microvessels in the rat mesentery.

Structural alterations in the rat kidney after acute arsine exposure.

The mechanism of arsine (AsH3) toxicity is not completely understood. In this investigation, the toxicity of AsH3 and AsH3-produced hemolytic products was determined in primary culture of renal cortical epithelial cells and in the in situ isolated rat kidney. The objective of this study was to model kidney dysfunction caused by AsH3 exposure. The hypothesis was that unchanged AsH3 and AsH3-produced hemolysate that may contain arsenite (As(III)) as metabolite are both responsible for renal toxicity. Toxicity in isolated cells was determined by 2, 3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide inner salt (XTT) bioreduction, intracellular potassium (K+), and lactate dehydrogenase (LDH) leakage. Data from XTT bioreduction showed that most toxicity occurred at 1 hour and was independent of the arsenic species. At 4 hours, the observed toxicity depended on the arsenic species and was generated by As(III). In the isolated cells, the As(III)-spiked hemolysate produced similar toxicities with regard to intracellular K+ and LDH. The AsH3-hemolysate only affected LDH at 1 hour. Unchanged AsH3 was very toxic to the isolated rat kidney. In this system, after 10 minutes exposure to AsH3, the effects of toxicity were observed mainly in the glomerular and peritubular endothelial cells. Tubular epithelial cells also presented early signs of toxicity. The AsH3-hemolysate was not toxic after a 10-minute exposure. These data suggested that early cytotoxicity caused by unchanged AsH3 results in kidney dysfunction, produced by AsH3, and later by the formation of a hemolysate that may contain As(III). These data may be important in understanding the renal toxic effects after AsH3 intoxication.

Inflectional morphology in primary progressive aphasia: An elicited production study

Inflectional morphology lies at the intersection of phonology, syntax and the lexicon, three language domains that are differentially impacted in the three main variants of primary progressive aphasia (PPA). To characterize spared and impaired aspects of inflectional morphology in PPA, we elicited inflectional morphemes in 48 individuals with PPA and 13 healthy age-matched controls. We varied the factors of regularity, frequency, word class, and lexicality, and used voxel-based morphometry to identify brain regions where atrophy was predictive of deficits on particular conditions. All three PPA variants showed deficits in inflectional morphology, with the specific nature of the deficits dependent on the anatomical and linguistic features of each variant. Deficits in inflecting low-frequency irregular words were associated with semantic PPA, with lexical/semantic deficits, and with left temporal atrophy. Deficits in inflecting pseudowords were associated with non-fluent/agrammatic and logopenic variants, with phonological deficits, and with left frontal and parietal atrophy.

Acute blood stasis reduces interstitial uptake of albumin from intestinal microcirculatory networks

Temporary blood flow stoppage occurs in a greater percentage of the capillaries when blood flow to organs is reduced. Previous studies on the small intestine have suggested that acute blood stasis (≤10 min) results in expression of negative charge, not present when blood flow is brisk, on the luminal surface of mucosal capillaries. Negative surface charge would tend to reduce transcapillary passage of albumin from blood to interstitium, since albumin is also negatively charged. Here we test the hypothesis that acute blood stasis reduces the interstitial uptake of albumin from mucosal capillary networks in rat small intestine in situ. Animals were subjected to two treatments, which included intestinal blood flow and acute stasis. After each treatment, fluorescent albumins were perfused into the intestinal circulation, and then interstitial fluorescence was recorded using fluorescence microscopy. Images were later quantified by computer analysis. After brisk blood flow, but not after acute blood stasis, fluorescence rapidly appeared in the interstitium and resulted in higher interstitial fluorescence intensity values. These results may have relevance to the mechanisms by which albumin flux in the small intestine is synchronized with digestion and fasting, which are associated with high and low intestinal blood flow, respectively.