A morphometric and functional study of the toxicity of atmospheric ammonia in the extrathoracic airways in pigs

The effects of atmospheric ammonia (NH₃) on the nasal and tracheal mucosa of pigs were investigated by morphometric and functional methods. Pigs were exposed to four concentrations of NH₃ [5 (control), 25, 50 and 100 ppm] for 6 days in a specially designed air-pollutant exposure chamber. Samples were taken from the turbinates and the trachea, and the respiratory mucosa was examined by light and scanning electron microscopy. Dose-response curves to carbachol and isoproterenol were constructed using isolated strips of tracheal smooth muscle, with or without epithelium. In pigs exposed to ammonia, considerable mucosal injuries were observed in the turbinates but not in the trachea. The number of neutrophils in the epithelial layer and in the lamina propria, and epithelial hyperplasia were closely and significantly correlated with the concentrations of ammonia (r=0.894, p<0.001; r=0.727, p<0.001; and r=0.818, p<0.001, respectively). Except for the lamina propria, all these changes were significant (p<0.05) at ammonia concentrations as low as 25 ppm. The percentage of the surface of the turbinate mucosa that was ciliated tended to decrease with increasing ammonia concentration (r=0.439, p<0.082). Ammonia induced smooth-muscle hyperresponsiveness to carbachol with a close linear correlation between individual values of the carbachol-induced maximal effect and the NH₃ concentrations (r=0.526, p<0.003). While mechanical destruction of the epithelium induced an increase in E _max in the control group, no difference was observed between the intact and denuded strips from animals exposed to ammonia. The response to isoproterenol was not influenced by ammonia. It was concluded that quantitative histological analysis of the inflammatory infiltration and epithelial hyperplasia in the turbinates is a useful tool for quantifying the effects of atmospheric pollutants in pigs; a 6-day exposure to ammonia induces nasal irritation and functional disturbances of the tracheal smooth-muscle contractions at concentrations as low as 25 ppm.Abbreviations E _max maximal effect - IM intramuscularly - IV intravenously - NAL nasal lavage - pD ₂ negative logarithm of the molar concentration of agonist which induces an increase in tension equivalent to 50% of the maximal effect E _max expressed as grams force per mg of dry weight - r correlation coefficient     

RADIOGRAPHIC QUANTIFICATION OF TRACHEAL DIMENSIONS OF THE NORMAL THOROUGHBRED HORSE

Radiographic measurement of tracheal dimensions in the horse may be useful in evaluating upper and lower respiratory tract conditions due to the gradient of pressure changes between these areas. Lateral radiographs of the trachea of 15 normal sedated Thoroughbred horses were made at inspiration and expiration and magnification-corrected mean airway heights measured were, respectively: larynx: 5.89 and 5.86 cm; trachea at the third cervical vertebra (C3): 4.17 and 4.04 cm; at the fifth cervical vertebra (C5): 3.62 and 3.59 cm; at the first thoracic vertebra (T1): 3.4 and 3.23 cm; and carina: 3.85 and 4.12 cm. The ratio of airway height to nearby vertebral body lengths, at inspiration and expiration were, respectively: laryngeal height at C3: 0.56 and 0.56; tracheal height at C3: 0.4 and 0.39; at C5: 0.37 and 0.37; at T1: 0.59 and 0.59; and carina height: 0.91 and 0.94. The ratio of tracheal height to the thoracic inlet at inspiration and expiration was, respectively, 0.15 and 0.15. There was not a statistically significant association between airway diameter and phase of respiration. No association was found between tracheal height and body mass or height at the withers. Radiographic tracheal height can be measured independent of respiratory phase in sedated horses. It is suggested that the ratio of tracheal height to an adjacent bony landmark is more reliable for comparison between horses and tracheal height measurement should be made at C5, due to a lower standard deviation. If only thoracic radiographs are made, measurements of tracheal height at the thoracic inlet may be valuable.     

The influence of ageing on muscarinic receptors, β-adrenoceptors and adenylate cyclase activity in the bovine lung

Muscarinic and -adrenoceptors were identified in airway epithelium, smooth muscle and lung parenchyma from Holstein-Friesian calves and cows and were characterized with [³H]quinuclidinyl benzilate and [³H]dihydroalprenolol, respectively. The muscarinic receptor density in the smooth muscle of cows (B _max=4803±245 fmol/mg protein) was 33% greater (p<0.01) than in calves. Low receptor numbers were detected in the epithelium and parenchyma. In both calves and cows, the density of epithelial -adrenoceptors was twice as high as in smooth muscle and parenchyma. The quantity of -adrenoceptors in the tracheal epithelium (B _max=994±83 fmol/mg protein) and smooth muscle (B _max=492±41 fmol/mg protein) in cows was respectively 37% (p<0.001) and 35% (p<0.01) lower than in calves. Adenylate cyclase (AC) assays indicated that the basal and the (–)-isopropylnoradrenaline- (ISO-) stimulated cAMP production were not significantly different between the calves and cows. After stimulation with NaF, significantly higher cAMP production was found in all tissues from cows. Significant correlations were found between absolute AC responses to NaF and -adrenoceptor density in epithelium (r=–0.75,p<0.001) and smooth muscle (r=–0.63,p<0.01). It seems that, in older animals, the production of cAMP is independent of the number of receptors, indicating the presence of fully active compensatory mechanisms.Abbreviations AC adenylate cyclase - cAMP intra-cellular adenosine monophosphate - G-protein GTP binding protein - GTP guanosine 5-triphosphate - ISO isopropylnoradrenaline - M muscarine - QNB quinuclidinyl benzilate     

Muscarinic receptor subtypes, β-adrenoceptors and cAMP in the tracheal smooth muscle of conventional and double-muscled calves

The total muscarinic (M₁ + M₂ + M₃) and -adrenergic receptors in the tracheal smooth muscle of conventional and double-muscled calves were identified and characterized with the non-specific antagonists [³H]quinuclidinyl benzilate ([³H]QNB) and [³H]dihydroalprenolol ([³H]DHA) respectively.Although the quantity of -adrenoceptors in double-muscled calves was 25% lower (p<0.05) than in conventional calves (B _max=327±89 fmol/mg protein), adenylate cyclase assays indicated that the basal adenylate cyclase activity and the (–)-isopropylnoradrenaline (ISO)- and sodium fluoride (NaF)-stimulated values were not significantly different between these calves. However, the density of muscarinic receptors in double-muscled calves was 40% higher (p<0.01) than in conventional calves (B _max=2955±625 fmol/mg protein). Subtypes of muscarinic receptors were studied with [³H]telenzepine (M₁-receptors), [³H]AF-DX 384 (M₂-receptors) and [³H]4DAMP (M₁ and M₃-receptors). It was found that in both double-muscled and conventional calves about 40% of the receptors were of the M₃-subtype, the remaining 60% being M₂-receptors.From these results, it is suggested that inflammation of the respiratory tract in double-muscled calves may be complicated by an imbalance between the cholinergic bronchoconstrictor and the -adrenergic bronchodilator components of the autonomic nervous system.     

Adenosquamous Carcinoma of the Trachea in a Domestic Ferret (Mustela putorius furo)

A 4-year-old, castrated, male domestic ferret (Mustela putorius furo) was evaluated for a possible upper respiratory tract infection and wheezing for approximately 3 weeks. Supportive care for a suspected upper respiratory tract infection was initiated; however, the patient became progressively more dyspneic over the next 48 hours. A possible tracheal mass was identified upon thoracic radiographic imaging of the ferret. Tracheoscopy and a computed tomography scan of the neck and thorax confirmed the presence of a tracheal mass approximately 3 cm from the larynx obstructing 80% of the tracheal lumen. Rather than pursuing surgical resection, the owners elected humane euthanasia. An adenosquamous carcinoma of the trachea was diagnosed after histologic analysis. This tumor type has been diagnosed in the lungs of ferrets that were experimentally exposed to carcinogens found in cigarette smoke; however, there are no previous reports of this or any other tumor type associated with the ferret trachea. A tracheal mass causing a partial upper airway obstruction should be considered within the differential disease diagnosis list when a ferret is presented with dyspnea.     

Endotracheal tube placement during computed tomography of brachycephalic dogs alters upper airway dimensional measurements

Computed tomography (CT) is used to document upper airway lesions in dogs with brachycephalic obstructive airway syndrome. The presence of an endotracheal tube during CT scanning is often required for general anesthesia. We hypothesized that the endotracheal tube placement would change the soft tissue dimensions of the upper airway. The aims of this prospective, method comparison study were to evaluate the reliability of the previously reported upper airway CT measurements with endotracheal tube placement, and to propose measurements that are minimally affected by the endotracheal tube. Twenty brachycephalic dogs were included in this study. Each dog underwent head/neck CT with an endotracheal tube, followed by a second scan without the endotracheal tube. Ten measurements of the soft palate, nasopharynx, and trachea were performed. Tracheal dimension was significantly larger with the endotracheal tube compared to without, whereas the soft palate cross‐sectional area was significantly smaller with the endotracheal tube than without the endotracheal tube. The influence of the endotracheal tube on the caudal nasopharynx cross‐sectional (transverse‐sectional) area varied with a mean proportional absolute difference of 35%. Rostral soft palate thickness, tracheal perimeter, and cross‐sectional area of the rostral nasopharynx were the measurements least affected by the endotracheal tube (intraclass correlation coefficient = 0.964, 0.967, and 0.951, respectively). Therefore, we proposed that these three measurements may be most useful for future brachycephalic obstructive airway syndrome studies that require CT scanning of intubated animals. However, with endotracheal tube placement, measurements of soft palate length, caudal nasopharyngeal cross‐sectional area, and trachea height and width may not be reliable.     

Evaluation of recovery of Salmonella from trachea and ceca in commercial poultry

Unpublished data from our laboratory suggest that the respiratory tract may be a viable portal of entry for Salmonella infection. Further, field reports have indicated that tracheal sampling can be a sensitive tool for monitoring for Salmonella incidence in commercial flocks. In the present study we conducted a series of field trials in North and South America to evaluate the association between cecal and tracheal recovery of Salmonella in chickens and turkeys from commercial flocks. Environmental humidity and temperature were measured to evaluate their effects on frequency of isolation from the organs. Salmonella was recovered from tracheal samples in all trials. In 3 of the 4 trials in which both trachea and ceca were sampled, the incidence of Salmonella recovery was higher in tracheal samples. Though Salmonella was not recovered from ceca in trial 2, 5% of liver and spleen samples indicated infection. Environmental conditions were not associated with incidence of Salmonella recovery. These data suggest that tracheal contamination can be a good indicator of Salmonella infection under commercial poultry conditions.     

Histomorphology of the lower respiratory tract in the Indian crested porcupine (Hystrix indica)

The Indian crested porcupine (Hystrix indica) (ICP) is widely distributed in Asia; however, compared with other rodents, little is known about the structures of its respiratory system. The aim of this study was to evaluate the histomorphology of the lower respiratory portion of the ICP to provide a basis for the identification of the normal structure of this organ. The larynx, trachea and lungs of four carcasses of adult Indian crested porcupines (two males and two females) were dissected and fixed in 10% neutral-buffered formalin. The gross anatomy and histology of all specimens were evaluated. A macroscopic evaluation showed unique structures in the ICP respiratory system, including the presence of a chamber-like structure at the origin of the bronchi and a difference in epiglottis shape between males and females. Histologically, the stratified squamous epithelium covered the epiglottis and arytenoid cartilage, and the pseudostratified ciliated columnar epithelium covered the internal part of the thyroid and cricoid cartilages. Histomorphological studies showed a few goblet cells in the tracheal epithelium. In the bronchi and larger bronchioles, pseudostratified ciliated columnar epithelia were observed. Bronchi were surrounded by segments of cartilage. Distal bronchioles had a simple cuboidal/columnar epithelium with club (Clara) cells, lacked cartilaginous tissue in their walls and had a complete smooth muscle layer. These results revealed histomorphological differences between the ICP and other rodents.