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Biomedical subjects

A Tucker

Publications and source records attributed to A Tucker.

At least 91 records · Page 5Linked to original sources
PubMed1991

Pulmonary particle deposition and airway mucociliary clearance in cold-exposed calves.

Effect of cold-induced changes in respiratory pattern on pulmonary particle deposition was investigated in 10 male Holstein calves between the ages of 1 and 3 months. Deposition of intranasally instilled fluorescence-enhanced Pasteurella haemolytica was significantly higher (P less than 0.05) for cold-exposed calves and appears to be caused by the cold-induced respiratory pattern change. Deposition was greater in apical and mediastinal lung lobes, but the reason for this preferential deposition is uncertain. Nasal mucus velocity was measured in 4 nonanesthetized calves at ambient temperature of 2 to 4 C and 16 to 18 C, using tantalum-paraffin oil droplets and serial radiography. Nasal mucus velocity was 24% lower during cold exposure. In addition, the effect of mucosal temperature on tracheal mucus velocity was determined in excised tracheas from 7 calves. A direct relationship existed between mucosal temperature and tracheal mucus velocity within the mucosal temperature range studied (35.0 to 39.5 C). Tracheal air temperature measurements in calves at ambient temperatures of -10.4 C (n = 4) and 18.5 C (n = 5) indicated that conditioning of inspired air is not complete at the tracheal level during extreme cold exposure. Therefore, cold air may directly influence tracheal mucociliary clearance. It is speculated that cold exposure increases pulmonary deposition of pathogens, while simultaneously decreasing mucociliary clearance of the upper airways, thus predisposing cold-exposed calves to respiratory tract infection.

Animals↗
PubMed1991

Vascular cells respond differentially to transforming growth factors beta 1 and beta 2 in vitro.

Transforming growth factor beta 1 (TGF-beta 1) and beta 2 (TGF-beta 2) are equipotent in many cell systems studies thus far. Recent data, however, show different effects elicited by these two growth factors in specific biologic systems. This investigation compares the effects of TGF-beta 1 and TGF-beta 2 bovine aortic endothelial cells (BAECs), rat epididymal fat pad microvascular endothelium (RFCs), and bovine aortic smooth muscle cells (BASCs). In two-dimensional cultures, proliferation of BAECs, BASMCs, and RFCs were all inhibited by TGF-beta 1, while in response to TGF-beta 2, BASMCs were fully inhibited, RFCs were modestly inhibited, and BAECs were unaffected. Bovine aortic endothelial cell migration was significantly inhibited by TGF-beta 1, but only slightly inhibited by TGF-beta 2. In contrast, BASMC migration was enhanced by TGF-beta 1 and was not affected by TGF-beta 2. In three-dimensional cultures, RFCs were stimulated to undergo in vitro angiogenesis in response to TGF-beta 1 and TGF-beta 2 at 10-fold higher concentrations. Three distinct receptor assays demonstrated the presence of type I and type II TGF-beta 1 cell-surface-binding proteins on BAECs, BASMCs, and RFCs. Labeled TGF-beta 1 was competed off completely with 100-fold molar excess unlabeled TGF-beta 1, but only partially with equivalent excess unlabeled TGF-beta 2. Furthermore the ratios of type I to type II TGF-beta receptors in these three vascular cell types vary from 1:1 in BAECs to 1.5:1 in RFCs to 3:1 in BASMCs and can be correlated with the differences noted in cellular responses to TGF-beta 1 and TGF-beta 2 in proliferation, migration, and in vitro angiogenic assays. These findings support the hypothesis that there are different responses to the TGF-beta s, depending on the cell type and experimental conditions as well as the TGF-beta concentration and isoform used.

Animals↗
PubMed1990

Colicins: prokaryotic killer-pores.

Colicins are plasmid-encoded protein antibiotics which kill bacteria closely related to the producing strain (generally Escherichia coli). The study of the function of colicins has revealed many features which reflect common targeting and translocation mechanisms with bacteriophages and toxins. Like many toxins, colicins are composed of structural domains specialized in one of the different steps of the activity, targeting, translocation and killing. The major group comprises those colicins which permeabilize the cytoplasmic membrane, thereby destroying the cell's membrane potential. These colicins form well-defined voltage-gated ion channels in artificial membranes. The scope of this review is to describe some of the more recent findings concerning the structure and mode of action of pore-forming colicins with a special attention to models of membrane insertion and pore structure based on the recently determined three-dimensional structure of the pore-forming domain of colicin A.

Amino Acid Sequence↗
PubMed1990

Metabolic consequences of reduced frequency breathing during submaximal exercise at moderate altitude.

The intention of this study was to determine the metabolic consequences of reduced frequency breathing (RFB) at total lung capacity (TLC) in competitive cyclists during submaximal exercise at moderate altitude (1520 m; barometric pressure, PB = 84.6 kPa; 635 mm Hg). Nine trained males performed an RFB exercise test (10 breaths.min-1) and a normal breathing exercise test at 75-85% of the ventilatory threshold intensity for 6 min on separate days. RFB exercise induced significant (P less than 0.05) decreases in ventilation (VE), carbon dioxide production (VCO2), respiratory exchange ratio (RER), ventilatory equivalent for O2 consumption (VE/VO2), arterial O2 saturation and increases in heart rate and venous lactate concentration, while maintaining a similar O2 consumption (VO2). During recovery from RFB exercise (spontaneous breathing) a significant (P less than 0.05) decreases in blood pH was detected along with increases in VE, VO2, VCO2, RER, and venous partial pressure of carbon dioxide. The results indicate that voluntary hypoventilation at TLC, during submaximal cycling exercise at moderate altitude, elicits systemic hypercapnia, arterial hypoxemia, tissue hypoxia and acidosis. These data suggest that RFB exercise at moderate altitude causes an increase in energy production from glycolytic pathways above that which occurs with normal breathing.

Adult↗
PubMed1990

Lung volumes and maximal respiratory pressures in collegiate swimmers and runners.

To determine whether respiratory muscle strength is related to pulmonary volume differences in athletes and nonathletes, 11 intercollegiate female swimmers, 11 female cross-country runners, and two nonathletic control groups, matched to the athletes in height and age, were evaluated for pulmonary parameters including maximal inspiratory pressure (PImax) and maximal expiratory pressure (PEmax). Swimmers exhibited larger (p less than .05) vital capacities (VC), residual lung volumes (RV), inspiratory capacities (IC), and functional residual capacities (FRC) than both the runners or the controls but no difference (p greater than .05) in either PImax or inspiratory flow (FIV 25%-75%). Timed expiratory volumes (FEV 0.5 and FEV 1.0) were significantly (p less than .05) lower in the swimmers than in the controls. These data suggest that an adaptational growth may be responsible, in part, for the augmented static lung volumes demonstrated in swimmers.

Adolescent↗
PubMed1990

Hepatobiliary cystadenoma with mesenchymal stroma.

In a detailed review of cystic hepatobiliary neoplasms, we identified a subset of 50 cases in which tumors were characterized by the presence of a mesenchymal cell layer interposed between an inner epithelial lining and an outer connective tissue layer. We have recently seen three such patients, making a total of 53 patients reported in the English literature. All of the patients were female, 44 of whom, with an average age of 41 years, had benign tumors. The average age of the remaining nine patients was 57 years and these patients had malignant tumors. In seven patients, the malignancy arose from the epithelial layer, but in two patients sarcomatous changes were identified in the mesenchymal tissues. The older age of the patients with malignant tumors with adequate serial biopsies in two cases supported the thesis that malignant transformation may occur in the benign tumors. Moreover the location of the tumor in one of our patients in whom the resected tumor was associated with anomalous right hepatic ducts and portal veins supported the theory that these tumors develop embryologically from nests of primitive hepatobiliary endodermal and mesodermal cells. Although surgical treatment was performed in all patients, 25% of the patients with benign hepatobiliary cystadenoma with mesenchymal stroma (CMS), and 33% of the patients with malignant CMS had tumor recurrence after primary resection. Ninety per cent of these patients had an incomplete resection at the time of their initial operations. Forty-four per cent of the patients with malignant CMS died after a mean follow-up of 17 months. We conclude that CMS (Edmonson's tumor) occurs uniquely in young female patients, develops from nests of primitive embryonal cells, has the potential for malignant transformation, and should be completely resected at primary operation to avoid recurrence.

Adult↗
PubMed1990

Age-dependent effects of chronic hypoxia on renin-angiotensin and urinary excretions.

The mechanisms regulating water, electrolyte, and blood volume homeostasis continue to mature in early postnatal life, and this maturation may be altered by perturbations of volume or cardiovascular status. To evaluate the long-term effects of chronic hypoxia on water balance, urinary electrolyte excretion, heart weights, systemic arterial pressure, and components of the renin-angiotensin system, male Sprague-Dawley rats were exposed to periods of simulated altitude of 10,000 ft up to 90 days of age beginning at 2 or 30 days of age. Altitude exposure of both neonatal and adult rats was associated with increases in urine output and water intake after 30 days of exposure, and right ventricular (RV) hypertrophy at all ages was examined. However, the percent increase in urine output, water intake, and RV hypertrophy was numerically greater in neonates. Neonates also had increases in urinary sodium and potassium excretion after 30 days of exposure. Plasma renin activity and serum angiotensin-converting enzyme (ACE) activity were not affected, but plasma renin substrate was reduced in both neonatal and adult altitude-exposed rats. Lung ACE activity was also decreased in altitude-exposed neonates. These data indicate that the degree and, in some cases, the nature of these homeostatic responses varies with age during long-term hypoxia.

Altitude↗
PubMed1990

Cold-induced changes in breathing pattern as a strategy to reduce respiratory heat loss.

Thermoregulatory benefits of cold-induced changes in breathing pattern and mechanism(s) by which cold induces hypoventilation were investigated using male Holstein calves (1-3 mo old). Effects of ambient temperatures (Ta) between 4 and 18 degrees C on ventilatory parameters and respiratory heat loss (RHL) were determined in four calves. As Ta decreased, respiratory frequency decreased 29%, tidal volume increased 35%, total ventilation and RHL did not change, and the percentage of metabolic rate attributed to RHL decreased 26%. Total ventilation was stimulated by increasing inspired CO2 in six calves (Ta 4-6 degrees C), and a positive relationship existed between respiratory frequency and expired air temperature. Therefore, cold-exposed calves conserve respiratory heat by decreasing expired air temperature and dead space ventilation. Compared with thermoneutral exposure (16-18 degrees C), hypoventilation was induced by airway cold exposure (4-6 degrees C) alone and by exposing the body but not the airways to cold. Blocking nasal thermoreceptors with topical lidocaine during airway cold exposure prevented the ventilatory response but did not lower hypothalamic temperature. Hypothalamic cooling (Ta 16-18 degrees C) did not produce a ventilatory response. Thus, airway temperature but not hypothalamic temperature appears to control ventilation in cold-exposed calves.

Acclimatization↗
PubMed1990

Normoxic and acute hypoxic exercise tolerance in man following acetazolamide.

The influence of acetazolamide (ACZ) upon the ability to perform and sustain maximal and submaximal exercise bouts under normoxic and hypoxic conditions was examined in four groups of healthy male subjects (N = 27). ACZ (500 mg) or inert placebo (Pla) was administered prior to exercise in a quasi-randomized, double-blind, crossover fashion. ACZ was shown to lower venous pH (ACZ, 7.31 +/- 0.01, vs Pla, 7.35 +/- 0.08) and bicarbonate (ACZ, 22.4 +/- 0.27 mM, vs Pla, 25.4 +/- 0.6 mM) and to elevate urine pH (ACZ, 7.36 +/- 0.06, vs Pla, 5.84 +/- 0.19) and tended to elevate VE (P = 0.07) at rest. Peak VO2 measured using a continuous incremental protocol was unaltered in normoxia, while peak VCO2 and RER were lowered by ACZ. No significant effect of ACZ upon VO2, VCO2, RER, or heart rate (HR) was observed during submaximal exercise (75% of peak VO2) although VE was increased by 14% and time to exhaustion (EXHt) was reduced by 29%. During acute hypoxia at a simulated altitude of 4,270 m (Pbar = 446 mm Hg), no significant differences were noted in VE, VO2, VCO2, RER, HR, or arterial saturation (SaO2) at rest. Prior to exercise, venous pH (ACZ, 7.39 +/- 0.04, vs Pla, 7.44 +/- 0.007) and bicarbonate were lower with ACZ (ACZ, 21.6 +/- 0.46 mM, vs Pla, 24.2 +/- 0.25 mM), while urine pH was higher (ACZ, 7.6 +/- 0.07, vs Pla, 5.9 +/- 0.25). Other than a higher PCO2 and lower venous lactate with ACZ, no significant differences were identified at peak VO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetazolamide↗
PubMed1989

Crystallization of p68 on lipid monolayers and as three-dimensional single crystals.

Two-dimensional crystals of p68, a Ca2+ -binding protein that has homology with members of the lipocortin/calpactin family, were obtained by interaction with a phospholipid monolayer. By measuring surface pressure at constant surface area, p68 was found to interact in a Ca2+ -dependent manner specifically with phosphatidylethanolamine, less so with phosphatidylserine and not at all with phosphatidylcholine. With dimyristoyl-phosphatidylethanolamine, two-dimensional crystalline arrays were formed. Image analysis of electron micrographs of these crystals, which diffracted to about 50 A, revealed p3 symmetry with a unit cell of about 178 A by 178 A; the protein densities showed a two-domain structure giving a cylindrical molecule of about 100 A by 35 A diameter packed as trimers. Three-dimensional microcrystals obtained without lipid or Ca2+ were suitable for electron microscopy and gave a tetragonal unit cell of about 256 A by 68 A. The implications of these observations on the structure and lipid specificity of p68 binding are discussed.

Annexin A6↗
PubMed1989

Sympathetic and metabolic correlates of hypoxic moderation of spontaneous hypertension in the rat.

Exposure to hypobaric hypoxia (H; simulated altitude = 3658 m) was initiated in 5-week-old, male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKy) normotensive rats while normoxic controls (N) for both groups were maintained under laboratory conditions. Significant attenuation of systolic arterial blood pressure was evident in SHR-H relative to SHR-N (125 +/- 6 vs 145 +/- 5 mm Hg; P less than 0.05) but not in WKy-H relative to WKy-N (WKy-H, 116 +/- 2 vs WKy-N, 117 +/- 5 mm Hg). Hypoxia significantly decreased metabolic efficiency in both normotensive and hypertensive rats, although being both more severe and accompanied by significantly impaired growth rate in SHR-H. Urinary excretion of norepinephrine in the SHR was elevated relative to WKy, irrespective of altitude treatment, while hypoxia elicited similar increases in urinary excretion of norepinephrine in both SHR and WKy. Myocardial and adrenal contents of norepinephrine were significantly reduced following 3 days of simulated altitude exposure in both strains of rats. Tissue contents of norepinephrine in hypoxic rats returned to normoxic levels by 21 days of simulated altitude. Both urine and tissue indices provided consistent indirect evidence that changes in sympathetic neuronal activity in response to hypoxia were similar in normotensive and hypertensive rats. These findings suggest that prior reports of reduced alpha-adrenergic responsiveness in vasculature from hypoxia-exposed SHR reflect a postsynaptic event that is regulated independently of norepinephrine release from sympathetic nerve terminals.

Adrenal Glands↗
PubMed1989

Crystalloids in salivary gland pleomorphic adenomas.

Two types of crystalloids in salivary gland pleomorphic adenomas were studied by light microscopy and electron microscopy. The first type of crystalloid, the previously described tyrosine-rich crystalloid, was identified in three (1.5%) of 205 cases. The crystalloids by light microscopy assumed a radial configuration, resulting in the characteristic petal-shaped morphology. Transmission electron microscopy revealed them to be electron-dense, lobular projections without internal structure. Scanning electron microscopy demonstrated a range of morphology from rounded and intact doughnutlike structures to aggregates of irregular, loosely cohesive plates. The crystalloids were backscatter positive by backscattered electron imaging, and by x-ray microanalysis exhibited prominent calcium, phosphorus, and magnesium peaks that were not present in the adjacent tumor tissue; these three elements may be important in the formation and structure of tyrosine-rich crystalloids. The second type of crystalloid was intraductal and birefringent and was identified in 26 (12.7%) of 205 cases. In 21 of these 26 cases the crystalloids were lost on 10% formaldehyde fixation and paraffin embedding. Histochemical stains and x-ray microanalysis did not reveal a definite chemical composition, but did suggest a predominantly organic nature.

Adenoma, Pleomorphic↗
PubMed1989

Cardiopulmonary changes in conscious dogs with induced progressive pneumothorax.

Cardiopulmonary function was measured in 6 conscious dogs with progressive degrees of induced pneumothorax. Minute volume, respiratory rate, central venous pressure, systemic arterial pressure, pulmonary arterial pressure, pulmonary arterial occlusion pressure, heart rate, cardiac output, and arterial and mixed venous blood gases were determined before pneumothorax and at progressive volumes of pneumothorax equivalent to 50, 100, and 150% of the calculated lung volume. Tidal volume, pulmonary vascular resistance, alveolar to arterial O2 tension difference, physiologic dead space fraction, and pulmonary venous admixture also were calculated. Linear increases in respiratory rate, central venous pressure, alveolar to arterial O2 tension difference, and pulmonary venous admixture differed significantly (P less than 0.05). Linear decreases in tidal volume, pHv, pHa, PvO2, and PaO2 were also significantly different. Quadratic increases were significantly different for pulmonary arterial pressure and pulmonary vascular resistance. Trends were not significantly different for other values.

Animals↗