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Biomedical subjects

D D Smith

Publications and source records attributed to D D Smith.

At least 91 records · Page 5Linked to original sources
PubMed1987

Glutamine synthetase isozymes in elasmobranch brain and liver tissues.

Glutamine synthetase is present as isozymic forms in the elasmobranchs Squalus acanthias (dogfish shark) and Dasyatis sabina (stingray). Subcellular fractionation of elasmobranch brain and liver tissue shows the enzyme to be predominantly cytosolic in the former tissue and mitochondrial in the latter. For the cytosolic brain enzyme, the subunit Mr equals 42,000 in the stingray and 45,000 in the shark, as determined by sodium dodecyl sulfate-gel electrophoresis/Western blotting. The subunit Mr = 45,000 and 47,000, respectively, for stingray and dogfish mitochondrial liver enzymes. Translation of total brain RNA from both species gives immunoprecipitable nascent peptides of the same size as their respective mature enzymes. However, in liver tissue, translation of glutamine synthetase mRNA yields peptides of higher Mr than that of the mature enzymes. In dogfish liver, Mr = 50,000 for the translation product and, in stingray liver, Mr = 48,000. This suggests that the translocation of the enzyme into liver mitochondria may be via a signal or leader sequence mechanism. The larger liver isozyme of elasmobranch glutamine synthetase is found in kidney where it is also known to be mitochondrial. The smaller cytosolic isozyme occurs in retina, heart, gill, and rectal gland tissue as well as in brain.

Animals↗
PubMed1987

Uricoteley:its nature and origin during the evolution of tetrapod vertebrates.

The hepatic mechanism for detoxication of ammonia formed during amino acid gluconeogenesis in uricotelic vertebrates requires the intramitochondrial synthesis of glutamine by glutamine synthetase. This glutamine then serves as a precursor of uric acid in the cytosol. The evolutionary development of uricoteley thus required the localization of glutamine synthetase in liver mitochondria. The mechanism for the mitochondrial import of glutamine synthetase in uricotelic vertebrate liver is not yet known. Tortoises, extant relatives of the stem reptiles, possess both the ureotelic and uricotelic hepatic systems. It therefore seems likely that the genetic events allowing the mitochondrial localization of glutamine synthetase in liver occurred in the amniote amphibian ancestors of the stem reptiles. The selection of ureoteley by the theropsids and of uricoteley by the sauropsids were major events in the divergence and subsequent evolution of these two lines. Once established in the sauropsid line, uricoteley has persisted through to the higher reptiles, crocodilians, and birds. Uricoteley was in part responsible for the radiation of the archosaurs during the Triassic as a water-conserving mechanism in the adult, thereby allowing them to invade the arid environments of that period. Contrary to dogma, uricoteley was probably of minor significance in the development of the cleidoic egg. Neither mammalian nor avian embryonic liver tissues catabolize amino acids to any great extent, so it is inappropriate to attribute to them a kind of "waste" nitrogen metabolism.

Ammonia↗
PubMed1987

Glutamine synthetase in liver of the American alligator, Alligator mississippiensis.

Glutamine synthetase was shown to be localized in liver mitochondria of the American alligator, Alligator mississippiensis, by immunofluorescent staining of frozen liver sections and by the detection of enzymatic activity and immunoreactive protein in the mitochondrial fraction following subcellular fractionation of liver tissue by differential centrifugation. The primary translation product of alligator liver glutamine synthetase mRNA was shown to have an Mr = 45,000 which is similar if not identical in size to that of the mature subunit. This mRNA was found to be heterogeneous in size with a major form corresponding to 2.8-3.0 kb and a lesser form corresponding to around 2 kb. Both are in excess of the size required to code for the glutamine synthetase subunit. The synthesis and presumably the mitochondrial import of glutamine synthetase in alligator liver are thus very similar to the same processes in avian liver. Despite the excretion of a high percentage of nitrogen as ammonia, the demonstration of a mitochondrial glutamine synthetase indicates the alligator has the typical avian-type uricotelic ammonia-detoxification system in liver. This suggests that the transition to uricotelism occurred in the sauropsid line of evolution and has persisted through both the lepidosaurian (snakes, lizards) and archosaurian (dinosaurs, crocodilians, birds) lines.

Alligators and Crocodiles↗
PubMed1987

Evaluation of breathlessness in asbestos workers. Results of exercise testing.

We studied 120 asbestos-exposed workers seeking compensation for asbestos-related ventilatory impairment who were referred to us for evaluation of their complaint of dyspnea. We reviewed history, chest radiographs, pulmonary function studies, and exercise tests. The workers were 59.9 +/- 9.5 (mean +/- SD) yr of age and their first asbestos exposure had been 34.4 +/- 10 yr prior to the study; 63% were smokers, 19% were ex-smokers, and 18% were nonsmokers. Chest radiographs were normal in 4%, showed only pleural disease in 35%, only parenchymal diseases in 5%, and pleuroparenchymal disease in 56%. Restrictive pulmonary function abnormalities were present in 25% of the workers, and obstructive abnormalities were present in 27%. Because the impairment of one of several organ systems (i.e., ventilatory, cardiac, pulmonary vascular, or peripheral circulatory) may limit exercise performance, we designed an exercise test score in an attempt to identify the system causing the limitation. No abnormal limitation was detectable in half (49.2%) of the subjects. Only 26% had a ventilatory limitation, which was much more frequent in smokers (32%) than in nonsmokers (9%) (p less than 0.05). Unexpectedly, rather more (37%) had a cardiac rather than a ventilatory limitation. We conclude that the complaint of dyspnea in these asbestos-exposed workers was usually not caused by a ventilatory dysfunction.

Asbestosis↗
PubMed1987

Effects of interferon-gamma and other cytokines on collagen synthesis in fetal rat bone cultures.

Control of trabecular bone volume is mediated by local events. Recently, it has been shown that the cytokines interleukin-1 (IL-1), tumor necrosis factor alpha (TNF alpha), and TNF beta [also called lymphotoxin (LT)] produced by immune cells all stimulate osteoclast activity, whereas the lymphokine interferon-gamma (IFN gamma) inhibits osteoclast activity stimulated by these agents. We report here the effects of each of these cytokines on bone collagen content measured as incorporation of proline into collagen and noncollagen protein in 20-day-old fetal rat calvariae. We found that IL-1, LT, and TNF decreased bone collagen synthesis and, to a lesser degree, noncollagen protein synthesis when the bones were exposed continuously to these agents. In addition, these cytokines stimulated DNA synthesis in the calvariae. In contrast to its action on bone resorption, where it opposed the resorptive effects of IL-1, TNF, and LT, IFN gamma inhibited bone collagen synthesis and had an additive effect with TNF and LT when bones were exposed to both. However, unlike the other cytokines, IFN gamma also decreased DNA synthesis in the calvariae. These data indicate that cytokines released by immune cells in the bone marrow microenvironment may work in concert to affect osteoblast activity in vitro.

Animals↗
PubMed1986

Forskolin effects on longitudinal myometrial strips from the pregnant rat: relationship with membrane potential and cyclic AMP.

The effects of forskolin on tension, membrane potential and cyclic AMP accumulation were studied in longitudinal myometrial strips from pregnant rats. 0.1 microM forskolin reduced the amplitude of spontaneous contractions by decreasing the frequency of action potential discharge without a change in resting potential or cyclic AMP accumulation. Forskolin, 1.0 microM, abolished contractions and action potentials, hyperpolarized the membrane and increased cyclic AMP accumulation. Ouabain, 1 mM, depolarized the muscle and increased resting tension. Ouabain reduced potential change produced by forskolin but did not prevent the relaxation or cAMP accumulation. Therefore changes in membrane potential are not prerequisite for the inhibitory actions of forskolin. The cyclic AMP-related relaxation may result primarily from intracellular events that remove calcium from the contractile elements.

Animals↗
PubMed1986

Mannitol oxidase: partial purification and characterization of the membrane-bound enzyme from the snail Helix aspersa.

Mannitol oxidase, a membrane-bound oxidase has been purified 250-fold from snail digestive gland tissue. The activity is solubilized by a number of ionic, non-ionic, and zwitterionic detergents. Purification of the solubilized enzyme was by polyethylene glycol fractionation and column chromatography using anionic exchange resins, hydroxylapatite, and gel filtration. The enzyme is stabilized by glycerol and remains active for at least one week at -20 degrees. Hydrogen peroxide is the oxygen reduction product and a mannose/hydrogen peroxide stoichiometry of 0.86 was found. D-Arabinitol and D-mannitol were the most active substrates of those tested. Results with these and other substrates suggest that the configuration around carbons-2 and -4 is critical for binding and reactivity. The apparent Km for D-mannitol is 6 mM and for oxygen, 40 microM. The pH optimum for the enzyme is between 8 and 8.5 and the isoelectric point is 5.4-5.6.

Alcohol Oxidoreductases↗
PubMed1986

Human recombinant transforming growth factor alpha stimulates bone resorption and inhibits formation in vitro.

Human recombinant transforming growth factor alpha (TGF alpha), which binds to the epidermal growth factor (EGF) receptor and causes several biological effects similar to those caused by EGF, was compared with murine EGF for its effects on a number of parameters of bone cell metabolism. TGF alpha stimulated bone resorption in two organ culture systems, the fetal rat long bone and neonatal mouse calvarial systems. TGF alpha stimulated bone resorption at concentrations as low as 0.1 ng/ml. TGF alpha effects on bone resorption in mouse calvariae were inhibited by indomethacin, suggesting that, like EGF, its effects were mediated by prostaglandin synthesis. TGF alpha had a different time course of action on bone resorption from that of EGF, causing more rapid release of previously incorporated 45Ca from bone cultures, suggesting that TGF alpha does not function on bone as a simple EGF analogue. TGF alpha also caused effects on osteoblast function resembling those of EGF. It inhibited alkaline phosphatase activity in cultured rat osteosarcoma cells with the osteoblast phenotype and inhibited collagen synthesis in fetal rat calvaria at concentrations of 1.0 ng/ml. The lowest concentration of TGF alpha (expressed as nanogram equivalents of EGF per ml) required to produce a response in all of the systems tested was about 1/10th of that needed for EGF to produce a similar effect. These results indicate that TGF alpha is a potent stimulator of bone resorption and inhibitor of bone formation as assessed by inhibition of collagen synthesis and alkaline phosphatase activity and are consistent with the hypothesis that TGF alpha may be responsible, at least in part, for the bone resorption associated with some tumors.

Alkaline Phosphatase↗
PubMed1985

Methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate-cyclohydrolase-formyltetrahy dro folate synthetase. Affinity labelling of the dehydrogenase-cyclohydrolase active site.

Methylenetetrahydrofolate dehydrogenase and methenyltetrahydrofolate cyclohydrolase are inactivated in parallel by carbodiimide-activated folic acid in an NADP-dependent reaction. Modification with tritium-labelled reagent resulted in the incorporation of 1 mole 3H-folate per mole polypeptide, which demonstrates that these activities share a single folate binding site.

Affinity Labels↗
PubMed1985

EGF receptor antiserum inhibits bone resorbing activity produced by a rat Leydig cell tumor associated with the humoral hypercalcemia of malignancy.

The humoral hypercalcemia of malignancy (HHM) is a syndrome caused by tumor cells releasing unknown circulating factors which stimulate osteoclastic bone resorption. In the D6 variant of the rat Leydig cell tumor model of HHM, we found that tumor extracts and tumor cell conditioned medium contained a macromolecular bone resorbing factor which coeluted on column chromatography with transforming growth factor activity (TGF). This observation led to the hypothesis that the tumor-derived bone resorbing factor was a TGF which interacts with the epidermal growth factor (EGF) receptor. To test this hypothesis, we examined the effects of two classes of antisera to the EGF receptor on bone resorption stimulated by conditioned medium from Leydig D6 tumor cells using organ cultures of fetal rat long bones. The antiserum which blocks the binding of EGF to its receptor inhibited bone resorption stimulated by tumor conditioned medium and by EGF. The second antiserum to the EGF receptor which does not block EGF binding or biological activity had no effect on bone resorption stimulated by either tumor conditioned medium or EGF. Neither antiserum had any effect on bone resorption stimulated by parathyroid hormone (PTH). These results indicate that the tumor-derived bone resorbing factor is dependent upon the availability of EGF receptors for its activity and are consistent with it being a TGF.

Animals↗
PubMed1985

Effects of accidental chlorine inhalation on pulmonary function.

In an industrial accident, 19 previously healthy workers were briefly exposed to high concentrations of chlorine gas. Pulmonary function tests were done at intervals for about two years but complete follow-up data were available in only 11 subjects. Immediately following the exposure, airway obstruction was detected in 10 of 19 patients; 700 days later this was found in only 3 of 11 patients. Two of these three patients had a history of smoking, however. The mean residual volume was 141% +/- 97 (mean +/- standard error of the mean) on day 1. In subsequent follow-up studies, the residual volume progressively fell in all patients, and 700 days later the mean residual volume was 90% +/- 5. In 5 of the 19 subjects, all pulmonary function test results were within normal limits on day 1. Apparently in some subjects acute exposure to chlorine gas may cause immediate changes in the lung functions, but these changes gradually resolve. Because of the small number of patients in our series, however, the long-term effects of chlorine are less apparent.

Accidents, Occupational↗
PubMed1984

Pathogens detected in the faeces of children with diarrhoea in a Sydney hospital.

During a 54-week period, faecal samples taken from 350 children under 5 years of age, who were admitted with acute diarrhoea to the infectious diseases ward of a Sydney hospital, were examined for pathogens. Rotavirus was detected as the sole agent in the specimens of 58 patients (16.6%), enteroviruses in those of 26 patients (7.4%), salmonellae in those of 19 patients (5.4%) and Campylobacter jejuni in those of 15 patients (4.3%). Shigellae were not detected. The results are discussed and, in view of the changing patterns of infection, it is suggested that there is a continuing need for research into the causes of enteritis in Australia.

Australia↗
PubMed1984

Besnoitia darlingi (Apicomplexa, Sarcocystidae, Toxoplasmatinae): transmission between opossums and cats.

Opossums (Didelphis marsupialis), act as intermediate hosts for Besnoitia darlingi and could be infected orally with sporozoites (oocysts) and bradyzoites (tissue cysts), or intraperitoneally (i.p.) with tachyzoites. Infections could presumably be transmitted through cannibalism. Cats (Felis catus), the definitive host, could be infected only with bradyzoites but not sporozoites. Oocysts shed by cats measure about 12 X 12 microns, resemble similarly sized oocysts of Toxoplasma gondii and Hammondia hammondi, and must be differentiated by the appearance of tissue cysts after experimental infection of intermediate hosts. Cats did not form tissue cysts of B. darlingi. Tachyzoites from the related B. jellisoni could be used in the Sabin-Feldman dye test to determine the development of antibody to B. darlingi in opossums after infection.

Animals↗
PubMed1984

Hepatic ammonia metabolism in a uricotelic treefrog Phyllomedusa sauvagei.

Glutamine synthetase, a mitochondrial enzyme in liver of uricotelic reptiles and birds, is present in the cytosolic compartment of Phyllomedusa sauvagei liver. The average level is sufficient to account for the rate of uric acid excretion by adult frogs but is far lower than that present in birds and reptiles. Except for lower carbamoylphosphate synthetase activity, the activities of the urea cycle enzymes in P. sauvagei liver are comparable with those in adult ureotelic amphibians. The subcellular distribution of the urea cycle enzymes is much the same as in ureotelic amphibians and mammals with the possible exception of the occurrence of a small percentage of the carbamoylphosphate synthetase and ornithine transacarbamylase activities in the cytosol. In keeping with the subcellular localization of the enzymes, citrulline, and not glutamine, is formed by isolated liver mitochondria. The rapid degradation of glutamine by these mitochondria suggests a high degree of compartmentation of glutamine in the cytosol of P. sauvagei if it is to function as a precursor of uric acid in this compartment.

Ammonia↗