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Biomedical subjects

D L Morgan

Publications and source records attributed to D L Morgan.

At least 91 records · Page 5Linked to original sources
PubMed1997

CS2-mediated cross-linking of erythrocyte spectrin and neurofilament protein: dose response and temporal relationship to the formation of axonal swellings.

Using model proteins, a mechanism for CS2-mediated covalent cross-linking of proteins has been demonstrated previously. The biologic importance of CS2-promoted protein cross-linking is apparent as a possible dosimeter of CS2 exposure and as a potential mechanism to account for the identical neuropathies produced by 2,5-hexanedione and CS2. The present investigation examines the utility of erythrocyte spectrin cross-linking as a biomarker of effect for inhalation exposure to CS2 and examines the ability of CS2 to cross-link neurofilament proteins, a potential neurotoxic target. Rats were exposed to CS2 via inhalation at control, 50-, 500-, and 800-ppm levels for 2, 4, 8, and 13 weeks and spectrin dimer formation was quantified using denaturing gel electrophoresis and densitometry. Neurofilament preparations were also obtained from spinal cords and examined for cross-linking using Western blotting methods. The results obtained for protein cross-linking were compared to morphologic changes in the cervical and lumbar spinal cord using light and electron microscopy. The spectrin dimer exhibited a cumulative dose response and was detectable at both the 50-ppm level employed that did not produce axonal swellings and prior to the development of axonal swellings for the 500- and 800-ppm levels used. Neurofilament protein cross-linking involved all three subunits and the temporal relationship of cross-linking was consistent with a contributing role in the development of axonal swellings. These results establish the sensitivity of spectrin cross-linking for evaluating inhalation exposures and extend the similarities observed for 2,5-hexanedione and CS2 in both clinical settings and in vitro models to their effects exerted on neurofilaments in the axon.

Administration, Inhalation↗
PubMed1997

Comparative pulmonary absorption, distribution, and toxicity of copper gallium diselenide, copper indium diselenide, and cadmium telluride in Sprague-Dawley rats.

Copper gallium diselenide (CGS), copper indium diselenide (CIS), and cadmium telluride (CdTe) are novel compounds used in the photovoltaic and semiconductor industries. This study was conducted to characterize the relative toxicities of these compounds and to evaluate the pulmonary absorption and distribution after intratracheal instillation. Female Sprague-Dawley rats were administered a single equimolar dose (70 mM) of CGS (21 mg/kg), CIS (24 mg/kg), CdTe (17 mg/kg), or saline by intratracheal instillation. Bronchoalveolar lavage fluid (BALF) protein, fibronectin, inflammatory cells, lung hydroxyproline, and tissue distribution were measured 1, 3, 7, 14, and 28 days after instillation. Relative lung weights were significantly increased in CIS- and CdTe-treated rats at most time points. Inflammatory lesions in the lungs consisting of an influx of macrophages, lymphocytes, and PMNs were most severe in CdTe-treated rats, intermediate in CIS-treated rats, and minimal in rats receiving CGS. Hyperplasia of alveolar type 2 cells was present in CIS- and CdTe-treated rats and was greatest in CdTe-treated rats. Pulmonary interstitial fibrosis was observed in CdTe-treated rats at all time points. All three compounds caused marked increases in total BALF cell numbers, with the greatest increase observed in CIS-treated rats. BALF protein, fibronectin, and lung hydroxyproline were significantly increased in all treated animals and were highest in CdTe-treated animals. There was no apparent pulmonary absorption or tissue distribution of CGS. Indium levels increased in extrapulmonary tissues of CIS-treated rats, although Cu and Se levels remained unchanged. CdTe was absorbed from the lung to a greater extent than CGS and CIS. Cd and Te levels decreased in the lung and increased in extrapulmonary tissues. Of these compounds CdTe presents the greatest potential health risk because it causes severe pulmonary inflammation and fibrosis and because it is readily absorbed from the lung may potentially cause extrapulmonary toxicity.

Absorption↗
PubMed1997

Changes in the mechanical properties of human and amphibian muscle after eccentric exercise.

Following a series of eccentric contractions, that is stretching of the muscle while generating active tension, the length-tension relationship of isolated amphibian muscle has been shown to shift towards longer muscle length (Katz 1939; Wood et al. 1993). Here we report observations of electrically stimulated ankle extensor muscles of nine human subjects, demonstrating a similar shift in optimum angle for torque generation [3.9 (1.5) degrees] following exercise on an inclined treadmill that involved eccentric contractions in one leg. (All values are means with the SEMs in parentheses). The shift in the unexercised, control leg was significantly less [mean 0.4 (0.7) degree P < 0.05]. Correlated with this shift was a drop in torque [25.1 (5.6)% for the experimental leg; 1.6 (0.7)% for the control leg, P < 0.002]. Optimum angles returned to pre-exercise values by 2 days post-exercise, while torque took a week to recover. A similar shift in optimum length [12 (1.3)% of rest length] was obtained for five toad (Bufo marinus) sartorius muscles subjected to 25 eccentric contractions. Isometrically contracted control muscles showed a smaller shift [3.5 (1.6)%, n = 5]. Accompanying the shift was a drop in tension of 46 (3)% after the eccentric contractions [control isometric, 23 (6)%, P < 0.0001]. By 5 h after the eccentric contractions the shift had returned to control values, while tension had not recovered. When viewed with an electron microscope, sartorius muscles fixed immediately after the eccentric contractions exhibited many small, and a few larger, regions of myofilament disruption. In muscles fixed 5 h after the contractions, no small regions of disruption were visible, and the number of large regions was no greater than in those muscles fixed immediately after the eccentric contractions. These disruptions are interpreted as the cause of the shift in length-tension relationship.

Adult↗
PubMed1997

Effects of various pretreatments on the hepatotoxicity of inhaled styrene in the B6C3F1 mouse.

1. The roles of cytochrome P450 monooxygenases (P450) and glutathione (GSH) in styrene hepatotoxicity were investigated in mice by pretreating with either phenobarbital (PB; P450 inducer), SKF 525A (P450 inhibitor), N-acetylcysteine (NAC; GSH precursor), or saline (vehicle control) prior to a 6-h exposure to either 500 ppm styrene on air. 2. Styrene caused hepatocellular degeneration or necrosis in all groups; these changes were more extensive and severe in mice pretreated with PB. Styrene significantly increased relative liver weights and serum ALT and SDH levels only in mice pretreated with PB. NAC did not prevent GSH depletion or hepatotoxicity. 3. In the fat of SKF 525A-pretreated mice a slight but statistically significant increase in styrene levels was observed, suggesting that metabolism was decreased; the SO/styrene ratio in the fat of PB-pretreated mice showed a slight, but statistically significant, increase indicating a slight increase in styrene metabolism. Neither SKF 525A nor PB caused changes in microsomal enzyme activity in vitro. 4. These results suggest that styrene may be activated by a pathway not totally dependent upon P450 enzyme activity, or more likely that PB and SKF 525A are not specific for the P450 enzymes involved in activation and detoxification of styrene.

Adipose Tissue↗
PubMed1997

Aboriginal philosophy and its impact on health care outcomes.

Philosophical perspective is an important factor influencing the health and health care outcomes of Aboriginal Australians. To date, the nature of the Aboriginal perspective and its differences from mainstream European thinking have been poorly understood. The negative impact that this has on the health and health care of Aboriginal people has been seriously neglected. We outline some of the important features of the philosophical perspective of Aboriginal Australians. We suggest ways in which the recognition of these views can inform changes in treatment settings and methods that can contribute to improvements in the health care outcomes of Aboriginal Australians.

Attitude to Health↗
PubMed1997

Alveolar macrophages stimulated with titanium dioxide, chrysotile asbestos, and residual oil fly ash upregulate the PDGF receptor-alpha on lung fibroblasts through an IL-1beta-dependent mechanism.

Enhanced proliferation of fibroblasts is a primary characteristic of lung fibrosis. Macrophage-secreted platelet-derived growth factor (PDGF) is a potent mitogen and chemoattractant for lung fibroblasts. The magnitude of the fibroblast PDGF response is dependent on the number of PDGF receptor alpha (PDGF-R alpha) relative to PDGF-R beta at the cell surface. We recently reported that upregulation of the PDGF-R alpha subtype by interleukin (IL)-1beta results in enhanced lung fibroblast proliferation in response to PDGF-AA, PDGF-AB, and PDGF-BB whereas transforming growth factor (TGF)-beta1 has the opposite effect. Both IL-1beta and TGF-beta1 are produced by particle-activated macrophages in vivo and in vitro. We studied the net effect of macrophage conditioned medium (MOCM), which contains both IL-1beta and TGF-beta1, on the expression of the lung fibroblast PDGF receptor system. MOCM obtained from unstimulated, titanium dioxide (TiO2)-, chrysotile asbestos-, or residual oil fly ash (ROFA)-exposed macrophages in vitro increased [125I]PDGF-AA binding 3-, 6-, 6-, and 20-fold, respectively. These increases correlated with increased PDGF-R alpha mRNA and protein expression as shown by northern and western assays. PDGF-AB and -BB-stimulated [3H]thymidine incorporation by fibroblasts was enhanced 5-, 5-, 10-, and 20-fold by pretreatment with MOCM from unstimulated, TiO2-, asbestos-, and ROFA-exposed macrophages, respectively. [125I]PDGF-AA binding experiments using the IL-1 receptor antagonist blocked the upregulatory effect of all MOCM samples. Latent TGF-beta1 present in MOCM was activated by acid treatment, inhibiting upregulation by approximately 60%, a result similar to experiments with IL-1beta and TGF-beta1 mixtures. Treatment with a TGF-beta neutralizing antibody restored full upregulatory activity to acidified MOCM. Thus activated macrophages increase lung fibroblast PDGF-R alpha primarily due to the secretion of IL-1beta. Intratracheal instillation of ROFA particles in rats induced a 2-fold increase in total lung PDGF-R alpha mRNA in vivo. These findings support the idea that macrophage-derived IL-1beta plays a key role in the initiation of a fibrotic response by increasing fibroblast PDGF-R alpha expression, thereby dramatically potentiating the mitogenic response to PDGF.

Animals↗
PubMed1997

Drugs detected in patients suspected of acute intoxication.

Drug screens were performed for 434 adult patients who presented to the Parkland Memorial Hospital Emergency Department with suspected acute drug overdose. The screening consisted of analysis of urine by automated high performance liquid chromatography (REMEDi) in combination with qualitative EMIT immunoassays. Selected patients also had ethanol measured in blood, salicylate and acetaminophen measured in serum, and urine specimens analyzed qualitatively for cannabinoids. Most patients (83.4%), regardless of age, race, or gender, had evidence of consumption of at least one drug. The drugs detected most often were ethanol (30.0%) and cocaine (23.7%). At least one of the nine most common drugs-of-abuse (amphetamines, barbiturates, benzodiazepines, cannabinoids, cocaine, ethanol, opiates, opioids, and phencyclidine) was detected in 64.5% of the specimens, and combinations of these drugs were present in 45.4%. For most drugs, age, gender, ethnicity, time of day, day of week, and indication for screening could not be used to predict the drug screen result.

Acetaminophen↗
PubMed1996

The effects of repeated active stretches on tension generation and myoplasmic calcium in frog single muscle fibres.

1. A series of contractions with stretches (eccentric contractions) beyond the optimal length for tension generation (optimum) were shown to induce a shift in that optimum in single muscle fibres of frog, as has been previously reported for whole muscles. Shifts averaging 0.129 micron (sarcomere)-1 or 6% were found, without apparent damage to the fibre. 2. The stiffness of fibres was found to fall during a stretch, even though tension was rising. In addition, the isometric stiffness fell as a result of a series of eccentric contractions. 3. Calcium-sensitive fluorescent dyes indicated that such contractions did not reduce the amplitude of the intracellular calcium transient, but did increase its duration. A rise in resting [Ca2+] was found to accompany damage, but not necessarily the shift in optimum. 4. The twitch potentiator nitrate was shown to increase myoplasmic [Ca2+] during twitch and tetani, but not to reverse the shift in optimum length due to eccentric contractions. Both eccentric contractions and twitch potentiation reduced the maximum stimulation rate to which a fibre could respond with propagated action potentials. 5. These results exclude reduced myoplasmic [Ca2+] as the cause of the shift in optimum length in this preparation.

Animals↗
PubMed1996

Cytogenetic effects in mice of divinylbenzene-55 inhalation.

Male B6C3F1 mice (8 weeks of age) were exposed by inhalation to divinylbenzene-55 (DVB-55), at target concentrations of 0, 25, 50 and 75 ppm for 6 h per day for 3 days. Following exposure the animals were killed blood smears were prepared for micronucleus (MN) analysis, and the spleens were removed and cultured for sister chromatid exchange (SCE) and chromosome aberration (CA) analyses. DVB-55 induced a dose dependent increase in SCE with the two highest doses reaching statistical significance. Similarly, there was a statistically significant although less pronounced increase in the frequency of CAs in splenocytes and MN in polychromatic erythrocytes. There was no indication of toxicity as measured by cell cycle kinetics in the splenocytes or the percentage of polychromatic erythrocytes in the peripheral blood smears. Thus, DVB-55 appears to be a weak genotoxicant in vivo.

Administration, Inhalation↗
PubMed1996

Quantitative analysis of sarcomere non-uniformities in active muscle following a stretch.

Electron microscopy of toad (Bufo marinus) muscle fixed without relaxing after a single eccentric contraction at muscle lengths greater than optimum showed over-stretched half-sarcomeres in sufficient numbers to account for more than half of the imposed stretch. Such sarcomeres were absent in another muscle fixed without relaxing after an isometric contraction at the same length and largely absent in a third muscle that underwent eccentric contraction at muscle lengths less than optimum. This provides direct evidence in support of the hypothesis that lengthening of muscles at long length involves lengthening of a few half sarcomeres to beyond filament overlap, while most half sarcomeres are extended much less than in proportion to muscle extension.

Animals↗
PubMed1996

Impulse initiation in the mammalian muscle spindle during combined fusimotor stimulation and succinyl choline infusion.

1. This is a report of observations on the responses of the primary and secondary endings of soleus muscle spindles of the anesthetized cat to the combined effects of the depolarizing neuromuscular blocker succinyl choline (SCh), given intravenously, and fusimotor stimulation. The findings were interpreted in terms of a dual pacemaker model for activity generated in the bag1 intrafusal fiber interacting with activity coming from bag2 and chain fibers. 2. In preliminary experiments it was found, using whole ventral root stimulation at fusimotor strength, that spindle responses to fusimotor stimulation were not blocked by SCh, whereas extrafusal junctions blocked rapidly. In the presence of SCh, fusimotor responses of spindle secondary endings were, on average, slightly larger than their control values before SCh was given, whereas fusimotor responses of primary endings were slightly smaller. 3. A study of the responses of spindle primary endings to stimulation of single dynamic (gamma D) and static (gamma S) axons in the presence of SCh revealed a fundamental difference in behavior. None of the responses to stimulation of gamma D axons (9 gamma D axons with 8 primary endings) showed significant summation with the responses to SCh. By contrast, the 20 gamma S axons studied showed varying degrees of summation with the responses to SCh. The responses of secondary endings to gamma S stimulation in the presence of SCh resembled those of primary endings and gamma S stimulation. 4. To explain these differences it is proposed that the primary ending has two separate sites of impulse initiation, one close to terminals on the bag1 intrafusal fiber (innervated by gamma D axons) and a second close to terminals on the bag2 and chain fibers (innervated by gamma S axons). It is proposed that the maintained increase in spindle firing observed during SCh infusion is the result of a bag2 contracture. The response to gamma S stimulation, contracting bag2 and chain fibers, adds to the SCh response. The degree of summation varies depending on whether the gamma S activates bag2 fibers, chain fibers, or both. The bag1 contracture, together with the effects of gamma D stimulation, acts through a separate pacemaker and therefore does not sum with the steady increase in spindle firing in the presence of SCh. There may be pacemaker switching between the bag1 generator and the bag2 and chain generator. 5. If the model is representative of most spindles containing the three kinds of intrafusal fibers, and the contractions of bag2 and chain fibers generate activity through a common impulse generator, then this bears on the question of the functional independence of the bag2 and chain fiber systems.

Animals↗
PubMed1996

Increasing ethnic diversity and managed care: how will they influence research patient recruitment in the nineties?

The challenge of research patient recruitment is intensifying in the 1990s. Relevant factors include the often negative impact of the press, increasing competition for patients, an increasingly ethnically diverse population, and a pervasive trend toward managed care. Based on preliminary findings from a patient focus group, 550 patients were contacted by mail and asked to complete a 25-item questionnaire. Survey results indicate that for most study patients initial telephone contact with a health care professional is not as important as the perception of a genuinely caring (i.e., "non-guinea pig") environment. Office location and other intangibles also affect recruitment; furthermore, several of the benefits sought by volunteers transcend ethnicity. The trend toward managed care will not impede and may enhance research patient recruitment. This research provides information and data that will enable investigators and sponsors to better meet the challenges of patient recruitment in the 1990s.

Adult↗
PubMed1995

Acute pulmonary toxicity of copper gallium diselenide, copper indium diselenide, and cadmium telluride intratracheally instilled into rats.

Acute toxicity studies were conducted on copper gallium diselenide (CGS), copper indium diselenide (CIS), and cadmium telluride (CT), three novel compounds used in the photovoltaic and semiconductor industries. Female Sprague-Dawley rats (six rats/dose) were administered 0, 12, 25, 50, or 100 mg/kg body wt of CGS, CIS, or CT by intratracheal instillation. At 72 hr after treatment, body weight gain was significantly decreased in the 100 mg/kg CIS group and in all CT dose groups. Lung weights were increased in most chemical-treated rats, with CT causing the greatest increase. Total numbers of cells in bronchoalveolar lavage fluid (BALF) were significantly increased in treated rats and were greatest in the 100 mg/kg CIS group. Differential cell counts of BALF demonstrated a marked decrease in the percentage of alveolar macrophages and an increase in the percentage of polymorphonuclear leukocytes in all dose groups of all three chemicals. Slight to moderate increases in lactate dehydrogenase activity were observed in BALF from CGS- and CIS-treated rats; marked increases were observed in CT-treated rats. BALF protein was significantly increased in rats treated with CIS and CT. Microscopic examination revealed lymphoid hyperplasia in lungs of rats treated with all three chemicals. CT caused necrosis of the terminal bronchiolar epithelium and epithelium of the alveolar duct region with inflammation, prominent fibrin exudates, and type II cell hyperplasia. CGS and CIS also caused intraalveolar inflammation and type II cell hyperplasia, but did not cause the necrosis and fibrin exudate observed in lungs of CT-treated rats. Based on changes in lung weight, BALF indices, and histopathology, CT was the most toxic for the lung; CIS had intermediate toxicity and CGS was the least toxic. The solubilities of CGS and CIS were relatively low and similar at both pH levels and do not readily explain the observed differences in pulmonary toxicity. The solubility of CdTe was considerably greater than that of CGS and CIS and likely contributed to the greater toxicity of this compound.

Animals↗
PubMed1995

Comparison of styrene hepatotoxicity in B6C3F1 and Swiss mice.

Inhalation exposure to styrene at concentrations that cause metabolic saturation results in significantly greater hepatotoxicity in B6C3F1 mice than in Swiss mice; females of both strains are more susceptible than males. These studies were conducted to investigate the mouse strain and gender differences in susceptibility to hepatotoxicity caused by repeated exposure to styrene at concentrations that do not cause metabolic saturation. Male and female B6C3F1 and Swiss mice (8 weeks old) were exposed to 0, 150, or 200 ppm styrene for 6 hr/day, 5 days/week, for up to 2 weeks. Changes in body and liver weights, serum alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) levels, liver histopathology, and total liver glutathione (GSH) were evaluated after 2, 3, 5, and 10 exposures (six mice/sex/strain/time point/concentration). Blood levels of styrene and styrene-7,8-oxide (SO) were measured in mice exposed to 200 ppm styrene for 2,3, or 5 days (six mice/sex/strain/time point/concentration). Serum ALT and SDH levels were significantly elevated only in female B6C3F1 mice after 3 exposures to 200 ppm styrene; enzyme levels had returned to control levels when measured after 5 and 10 exposures. Degeneration and coagulative necrosis of centrilobular hepatocytes were observed in female B6C3F1 mice exposed 2, 3, and 5 days to 150 or 200 ppm styrene; incidences of these lesions were greater in the 200 ppm than in the 150 ppm dose group. After 10 days of exposure to 150 or 200 ppm styrene, hepatocellular lesions had resolved, although a residual chronic inflammation was present in livers of most female B6C3F1 mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine Transaminase↗
PubMed1995

Early changes in sex hormones are not evident in mice exposed to the uterine carcinogens chloroethane or bromoethane.

Chloroethane and bromoethane have been shown to cause a marked uterine tumor response in B6C3F1 mice exposed for 2 years. These chemicals are nearly unique in this regard among the nearly 400 chemicals studied by the National Toxicology Program, and the reasons for this carcinogenic activity are unclear. The possible relationship of changes in blood concentrations of sex hormones to this response was evaluated by examining the estrous cycle of mice prior to and during a 21-day exposure to concentrations of the haloethanes which resulted in the tumorigenic response in the 2-year studies. Serum concentrations of estradiol and progesterone were determined at the termination of the exposures and compared to exposure group and stage of the estrous cycle. No consistent patterns of change were found in estrous cyclicity or in blood concentrations of sex hormones. Thus, the findings suggest that early changes in circulating sex hormones are not important contributing factors in the uterine neoplasia caused by these chemicals.

Animals↗
PubMed1995

Severe ethanol intoxication in an adolescent.

A 15-year-old boy presented to the emergency department with status epilepticus and a blood ethanol concentration of 757 mg/dL. Mechanical ventilation and substantial amounts of benzodiazepines were required. His hospital course was complicated by aspiration pneumonia, but he had no episodes of hypoglycemia. He received 2.8 hours of hemodialysis, which increased the rate of ethanol elimination, but there is no evidence that hemodialysis improved his clinical outcome. To our knowledge, this is the highest blood ethanol level reported in a child or adolescent who survived.

Adolescent↗