Platelet thrombus formation in microvessels of young spontaneously hypertensive rats

Vascular Effects on Cerebrovascular Permeability and Neurodegeneration

Neurons and glial cells in the brain are protected by the blood brain barrier (BBB). The local regulation of blood flow is determined by neurons and signal conducting cells called astrocytes. Although alterations in neurons and glial cells affect the function of neurons, the majority of effects are coming from other cells and organs of the body. Although it seems obvious that effects beginning in brain vasculature would play an important role in the development of various neuroinflammatory and neurodegenerative pathologies, significant interest has only been directed to the possible mechanisms involved in the development of vascular cognitive impairment and dementia (VCID) for the last decade. Presently, the National Institute of Neurological Disorders and Stroke applies considerable attention toward research related to VCID and vascular impairments during Alzheimer's disease. Thus, any changes in cerebral vessels, such as in blood flow, thrombogenesis, permeability, or others, which affect the proper vasculo-neuronal connection and interaction and result in neuronal degeneration that leads to memory decline should be considered as a subject of investigation under the VCID category. Out of several vascular effects that can trigger neurodegeneration, changes in cerebrovascular permeability seem to result in the most devastating effects. The present review emphasizes the importance of changes in the BBB and possible mechanisms primarily involving fibrinogen in the development and/or progression of neuroinflammatory and neurodegenerative diseases resulting in memory decline.

Temporal association between pulmonary and systemic effects of particulate matter in healthy and cardiovascular compromised rats

Exposure to particulate matter (PM) has been associated with increased morbidity and mortality among individuals with cardiovascular disease. It is hypothesized that systemic alterations occur concurrent to pulmonary injury/inflammation, and contribute to cardiac events in compromised hosts. We explored this hypothesis using a rat model for human hypertension and cardiovascular disease (spontaneously hypertensive, SH), and normotensive Wistar Kyoto (WKY) rats. SH and WKY rats (12-13 wk old) were exposed either intratracheally (IT; 0.0, 1.0, or 5.0 mg/kg in saline) or nose-only (15 mg/m(3) x 6 h/d x 3 d/wk x 1, 2 or 4 wk) to combustion source residual oil fly ash (ROFA) with low metal content, and examined 1, 2 or 4 d later. Bronchoalveolar lavage fluid (BALF) albumin and neutrophils increased (SH approximately equal WKY) at d 1 following ROFA IT. With inhalation exposure, both strains experienced progressive histological lung damage and increases in BALF albumin and neutrophils during 1 to 4 wk (SH > WKY). Acute lung injury from ROFA IT was temporally associated with increases in plasma fibrinogen in both strains, but only the SH rats responded to the acute 1-wk ROFA inhalation. Longer term (2 or 4 wk) ROFA caused progressive lung injury (SH > WKY), but did not sustain the increase in fibrinogen. BALF glutathione increased in a temporal fashion similar to fibrinogen; however, only WKY rats demonstrated this response. There was a small but consistent decrease in blood lymphocytes and an increase in blood neutrophils in SH rats exposed to ROFA acutely. In conclusion, acute PM exposure can provoke an acute systemic thrombogenic response associated with pulmonary injury/inflammation and oxidative stress in cardiovascular compromised rats. This evidence is consistent with greater cardiovascular events during acute PM episodes in compromised humans.

Molecular and genetic basis for thrombasthenic thrombopathia in otterhounds

OBJECTIVES

To determine the molecular and genetic basis for thrombasthenic thrombopathia in Otterhounds and establish whether the defect would be best classified as type-I Glanzmann's thrombasthenia.

ANIMALS

57 dogs, including 13 affected Otterhounds, 23 carrier Otterhounds, 17 unaffected Otterhounds, and 4 clinically normal unrelated dogs of other breeds.

PROCEDURE

Functional (platelet aggregation, clot retraction, buccal mucosa bleeding time) and biochemical (electrophoresis, flow cytometry, fibrinogen content) analyses were conducted. In addition, first-strand cDNA synthesis from platelet total RNA was performed. Exons of the genes encoding for glycoproteins (GP) IIb and IIIa were amplified in overlapping fashion. The resulting products were excised from agarose gels and sequenced. The sequences obtained were compared with known cDNA sequences for canine GPIIb and GPIIIa.

RESULTS

A single nucleotide change at position G1193 (1100) was detected in exon 12 of the gene encoding for platelet GPIIb in 2 affected Otterhounds. Carrier Otterhounds were heterozygous at this position, and 2 unaffected Otterhounds were unchanged. This nucleotide change would result in substitution of histidine for aspartic acid at position 398 (367) within the third calcium-binding domain of GPIIb.

CONCLUSIONS AND CLINICAL RELEVANCE

These studies suggest that thrombasthenic thrombopathia of Otterhounds is homologous phenotypically and has a similar molecular basis to type-I Glanzmann's thrombasthenia in humans.

Rodent models of susceptibility: what is their place in inhalation toxicology?

There is renewed interest in inhalation toxicology regarding 'susceptibility' as associated with host variables, including genetics, age, diet, and disease. This interest derives from epidemiology that shows air pollution-related human mortality/morbidity, especially among individuals with cardiopulmonary disease. Several animal models with experimental or genetically-based cardiopulmonary diseases are now being incorporated into inhalation toxicology studies to investigate mechanisms that underlie host susceptibility. However, current models have strengths and limitations as to how they mimic the essential features of human diseases. To date, animal models of pulmonary hypertension, bronchitis, asthma, and cardiovascular disease, but not emphysema, appear to exhibit greater susceptibility to air pollution particulate matter. As in humans, host susceptibility appears to involve multiple genetic and environmental factors, and is poorly understood, but the database of information is growing rapidly. As existing models gain wider use, our understanding of the models will improve and encourage refinements/development of models that integrate both genetic and environmental factors to better mimic the human condition.

BLOOD FLOW SHEAR RATES IN ARTERIOLES OF SPONTANEOUSLY HYPERTENSIVE RATS AT EARLY AND ESTABLISHED STAGES OF HYPERTENSION

Alterations of blood rheological properties can affect blood flow shear rates and therefore alter changes in the interactions between blood and vascular wall components during the development of hypertension. This study was done to evaluate alterations of blood flow shear rates in resistance vessels during the development of genetic hypertension in rats. In the current study, measurements were carried out on spontaneously hypertensive rats (SHR) during an early (3 weeks of age) and an established stage (12 weeks of age) of hypertension development. Age matched normotensive Wistar Kyoto (WKY) rats were used as controls. Intravital television microscopy was used to quantitate blood flow shear rates in first-(1A), second-(2A) and third-order (3A) arterioles of the cremaster muscle. In the young SHRs mean arterial blood pressure was not different from age matched WKY rats, but there was a significant increase of shear rate values in all observed (1A, 2A, 3A) arterioles of SHRs. However, shear rate values were significantly less in arterioles (1A, 2A, 3A) of SHRs with an established hypertension compared to the 3-week-old SHR group. We conclude that shear rates are elevated in resistance vessels prior to an increase in mean arterial pressure during the development of genetic hypertension. These results suggest that a change in blood rheology may cause a change in peripheral vascular resistance and thus contribute to the pathogenesis of hypertension.

The spontaneously hypertensive rat as a model of human cardiovascular disease: evidence of exacerbated cardiopulmonary injury and oxidative stress from inhaled emission particulate matter

Cardiovascular disease is considered a probable risk factor of particulate matter (PM)-related mortality and morbidity. It was hypothesized that rats with hereditary systemic hypertension and underlying cardiac disease would be more susceptible than healthy normotensive rats to pulmonary injury from inhaled residual oil fly ash (ROFA) PM. Eight spontaneously hypertensive (SH) and eight normotensive Wistar-Kyoto (WKY) rats (12-13 weeks old) were implanted with radiotelemetry transmitters on Day -10 for measurement of electrocardiographic (ECG) waveforms. These and other nonimplanted rats were exposed to filtered air or ROFA (containing leachable toxic levels of metals) on Day 0 by nose-only inhalation (ROFA, 15 mg/m(3) x 6 h/day x 3 days). ECGs were monitored during both exposure and nonexposure periods. At 0 or 18 h post-ROFA exposure, rats were assessed for airway hyperreactivity, pulmonary and cardiac histological lesions, bronchoalveolar lavage fluid (BALF) markers of lung injury, oxidative stress, and cytokine gene expression. Comparisons were made in two areas: (1) underlying cardiopulmonary complications of control SH rats in comparison to control WKY rats; and (2) ROFA-induced cardiopulmonary injury/inflammation and oxidative burden. With respect to the first area, control air-exposed SH rats had higher lung and left ventricular weights when compared to age-matched WKY rats. SH rats had hyporeactive airways to acetylcholine challenge. Lung histology revealed the presence of activated macrophages, neutrophils, and hemorrhage in control SHrats. Consistently, levels of BALF protein, macrophages, neutrophils, and red blood cells were also higher in SH rats. Thiobarbituric acid-reactive material in the BALF of air-exposed SH rats was significantly higher than that of WKY rats. Lung inflammation and lesions were mirrored in the higher basal levels of pulmonary cytokine mRNA expression. Cardiomyopathy and monocytic cell infiltration were apparent in the left ventricle of SH rats, along with increased cytokine expression. ECG demonstrated a depressed ST segment area in SH rats. With regard to the second area of comparison (ROFA-exposed rats), pulmonary histology indicated a slightly exacerbated pulmonary lesions including inflammatory response to ROFA in SH rats compared to WKY rats and ROFA-induced increases in BALF protein and albumin were significantly higher in SH rats than in WKY rats. In addition, ROFA caused an increase in BALF red blood cells in SH rats, indicating increased hemorrhage in the alveolar parenchyma. The number of alveolar macrophages increased more dramatically in SH rats following ROFA exposure, whereas neutrophils increased similarly in both strains. Despite greater pulmonary injury in SH rats, ROFA-induced increases in BALF GSH, ascorbate, and uric acid were attenuated when compared to WKY rats. ROFA inhalation exposure was associated with similar increases in pulmonary mRNA expression of IL-6, cellular fibronectin, and glucose-6-phosphate dehydrogenase (relative to that of beta-actin) in both rat strains. The expression of MIP-2 was increased in WKY but attenuated in SH rats. Thus, SH rats have underlying cardiac and pulmonary complications. When exposed to ROFA, SH rats exhibited exacerbated pulmonary injury, an attenuated antioxidant response, and acute depression in ST segment area of ECG, which is consistent with a greater susceptibility to adverse health effects of fugitive combustion PM. This study shows that the SH rat is a potentially useful model of genetically determined susceptibility with pulmonary and cardiovascular complications.