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Biomedical subjects

D R Nelson

Publications and source records attributed to D R Nelson.

At least 181 records · Page 10Linked to original sources
PubMed1988

On the membrane topology of vertebrate cytochrome P-450 proteins.

Hydropathy profiles of 34 aligned cytochrome P-450 sequences were compared to identify potential transmembrane segments. Eleven regions with the potential to cross a membrane in at least some P-450 sequences were detected. The known sidedness of several residues and peptides was used to eliminate some of these regions from consideration. Further arguments based on the location and orientation of the heme relative to the membrane excluded others. This process of elimination was continued until only two regions remained. These two segments, present in the first 66 amino acids of the P-450 NH2 termini, are proposed as the only transmembrane peptides of vertebrate microsomal P-450s. Mitochondrial P-450s may have a different membrane association. The three-dimensional structure of cytochrome P-450cam was examined for the location of conserved charged residues. These residues occurred mainly on the opposite surface from the substrate-binding site and along the edges of the flat triangular P-450cam. A model is proposed for vertebrate microsomal P-450s that is similar to P-450cam. The substrate-binding site faces the membrane, the heme is parallel to the membrane surface, and two NH2-terminal transmembrane segments anchor the protein to the bilayer.

Amino Acid Sequence↗
PubMed1988

Immunohistological localization of IgG1, IgA and secretory component in the bovine mammary gland during involution.

Immunoperoxidase methods were used to localize secretory component, immunoglobulin A and immunoglobulin G1 in mammary tissue from dairy cows. In lactating tissue, immunostaining for immunoglobulin A and secretory component was observed primarily in the luminal contents of alveoli. By day 2 of involution, alveolar epithelial cells stained for both immunoglobulin A and secretory component. Staining of alveolar epithelial cells for immunoglobulin A and secretory component continued throughout the period of mammary involution. No staining for secretory component was observed in the interalveolar stromal area. Immunoglobulin G1 immunostaining was localized primarily in the interalveolar areas in lactating tissue, but was localized at the apical and basolateral surface of alveolar cells on day 2 of involution. In contrast to immunoglobulin A, immunoglobulin G1 staining of epithelial cells did not persist and was primarily in the interalveolar areas by day 4. These results suggest that an increased localization of immunoglobulin G1 in bovine mammary epithelial cells may occur transiently in early involution, while an increase in immunoglobulin A and secretory component localization in epithelial cells persists throughout involution.

Animals↗
PubMed1988

Pharmacokinetics of N-nitrosodimethylamine in swine.

The pharmacokinetics of N-nitrosodimethylamine (NDMA) have been studied in swine. They were studied following i.v. administration of 0.1, 0.5 and 1.0 mg/kg, and following oral doses of 1.0 and 5.0 mg/kg of NDMA. Following a bolus i.v. dose, the concentration of NDMA in blood declined biphasically with a mean distribution half-life of 7 min and a mean elimination half-life of 28 min. The areas under the blood concentration versus time curves (AUC) were roughly proportional to dose indicating that the pharmacokinetics in this dose range were first order. The mean systemic clearance from blood was 65.8 ml/min/kg, the steady-state volume of distribution was 1.4 l/kg, and the mean residence time was 20 min. Following the oral doses, the AUC and peak concentration in blood were not proportional to the dose. It is likely that the pharmacokinetics at the lower dose were first order, but at the higher dose the pharmacokinetics were no longer first order because metabolism was saturated. The bioavailability of the 1.0 mg/kg dose was 67%. Since the clearance was probably due to metabolism and the clearance from blood exceeded hepatic blood flow, the high bioavailability suggests that extrahepatic metabolism plays an important role in the systemic clearance of NDMA in swine.

Animals↗
PubMed1988

Ileal carcinoid tumor complicated by retroperitoneal fibrosis and a prolactinoma.

A patient with mid-gut carcinoid tumor and the unusual complication of retroperitoneal fibrosis was also found to have a prolactinoma. This case brings the number of reported mid-gut carcinoid tumors complicated by a second endocrine neoplasm to five. Three of the second tumors were parathyroid in origin, and the fourth was an insulinoma. In view of the rarity of second tumors and in the absence of documented familial occurrence, it is inappropriate to exhaustively study each person with mid-gut carcinoid tumor, or their families, for a second endocrine neoplasm; however, physicians caring for patients with mid-gut carcinoid should be aware that second tumors are possible. Retroperitoneal fibrosis is also a rare complication of carcinoid, but can be associated with renal failure that can be prevented by surgical intervention. Thus, physicians caring for patients with the carcinoid syndrome should also be aware of this complication.

Carcinoid Tumor↗
PubMed1988

Cloning and characterization of the Aeromonas caviae recA gene and construction of an A. caviae recA mutant.

A recombinant plasmid carrying the recA gene of Aeromonas caviae was isolated from an A. caviae genomic library by complementation of an Escherichia coli recA mutant. The plasmid restored resistance to both UV irradiation and to the DNA-damaging agent methyl methanesulfonate in the E. coli recA mutant strain. The cloned gene also restored recombination proficiency as measured by the formation of lac+ recombinants from duplicated mutant lacZ genes and by the ability to propagate a strain of phage lambda (red gam) that requires host recombination functions for growth. The approximate location of the recA gene on the cloned DNA fragment was determined by constructing deletions and by the insertion of Tn5, both of which abolished the ability of the recombinant plasmid to complement the E. coli recA strains. A. caviae recA::Tn5 was introduced into A. caviae by P1 transduction. The resulting A. caviae recA mutant strain was considerably more sensitive to UV light than was its parent. Southern hybridization analysis indicated that the A. caviae recA gene has diverged from the recA genes from a variety of gram-negative bacteria, including A. hydrophila and A. sobria. Maxicell labeling experiments revealed that the RecA protein of A. caviae had an Mr of about 39,400.

Aeromonas↗
PubMed1988

Acceleration of starvation- and glycerol-induced myxospore formation by prior heat shock in Myxococcus xanthus.

The effect of heat shock on Myxococcus xanthus was investigated during both glycerol- and starvation-induced development. Cells heat shocked at 40 degrees C for 1 h prior to a development-inducing signal displayed an accelerated rate of myxospore formation at 30 degrees C. Additionally, M. xanthus cells heat shocked prior to glycerol induction formed a greater total number of myxospores when sporulation was complete than did control cells maintained at 30 degrees C. However, in starvation-induced fruiting cells the total number of myxospores in control and heat-shocked populations was about equal when fruiting body and myxospore formation was complete. When extended heat shock (3 h) was applied to cells prior to development, no acceleration of myxospore formation was observed. Heat shock elicited the premature expression of many developmentally regulated proteins. Cell fractionation and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography revealed the subcellular location and molecular weights of the 18 glycerol-induced and 9 starvation-induced developmental proteins. Comparison with previously identified M. xanthus heat shock proteins showed that nine of the developmental proteins found in glycerol-induced cells and three of the developmental proteins found in starvation-induced cells were heat shock proteins. Furthermore, heat shock increased the activity of alkaline phosphatase, a developmentally regulated enzyme, in vegetative cells, glycerol-induced cells, and starvation-induced cells.

Alkaline Phosphatase↗
PubMed1987

Biochemical effects of the antidepressant paroxetine, a specific 5-hydroxytryptamine uptake inhibitor.

Paroxetine was shown to be a potent (Ki = 1.1 nM) and specific inhibitor of [3H]-5-hydroxytryptamine (5-HT) uptake into rat cortical and hypothalamic synaptosomes in vitro. Lineweaver-Burk kinetic analysis determined that this inhibition was competitive in nature, implying a direct interaction with the 5-HT uptake transporter complex. Oral administration of paroxetine produced a dose-related inhibition of [3H]-5-HT uptake (ED50 = 1.9 mg/kg) into rat hypothalamic synaptosomes ex vivo with little effect on [3H]-l-noradrenaline (NA) uptake (ED50 greater than 30 mg/kg). This selectivity for 5-HT uptake was maintained after oral dosing for 14 days. Paroxetine (ED50 1-3 mg/kg PO) prevented the 5-HT depleting effect of p-chloroamphetamine (PCA) in rat brain, demonstrating 5-HT uptake blockade in vivo. Radioligand binding techniques in rat brain in vitro showed that paroxetine has little affinity for alpha 1, alpha 2 or beta adrenoceptors, dopamine (D2), 5-HT1, 5-HT2 or histamine (H1) receptors at concentrations below 1000 nM. Paroxetine demonstrated weak affinity for muscarinic receptors (Ki = 89 nM) but was at least 15 fold weaker than amitriptyline (Ki = 5.1 nM). Paroxetine, therefore, provides a useful pharmacological tool for investigating 5-HT systems and furthermore should be an antidepressant with reduced tricyclic-like side-effects.

Animals↗
PubMed1987

Evolution of cytochrome P-450 proteins.

Thirty-four cytochrome P-450 sequences from one bacterial and six vertebrate species have been aligned with the aid of a computer alignment algorithm. Phylogenetic trees were constructed using the unweighted-pair-group and neighbor-joining methods. The two trees differed at only a single branch point near the base of the tree. The cytochrome P-450 superfamily of proteins clustered into eight families and contained 16 gene-duplication events. The first gene duplication occurred approximately 1,360 Myr before the present (Mybp) and gave rise to cytochrome P-450s found in two different cellular organelles, the mitochondria and the endoplasmic reticulum. Both groups utilize cholesterol or its metabolites as substrates, implying that cholesterol existed greater than 1,360 Mybp. The fourth gene duplication (approximately 900 Mybp) gave rise to the drug-metabolizing P-450s. These proteins aid in the detoxification of foreign chemicals, as opposed to the metabolism of endogenous compounds. The importance of the capacity to metabolize drugs is reflected in 11 further gene duplications occurring in this lineage. The first occurred approximately 800 Mybp and gave rise to the two major P-450 families, the phenobarbital and 3-methylcholanthrene families. An apparent increase in the rate of cytochrome P-450 evolution is noted between the bird-mammal divergence (300 Mybp) and the mammalian radiation (75 Mybp).

Amino Acid Sequence↗
PubMed1987

Involution of the bovine mammary gland: histological and ultrastructural changes.

Bovine mammary tissue was collected by surgical biopsy at intervals during involution for histological and ultrastructural observation. In lactating tissue (d 0 of involution, collected 8 h after the final milking), alveolar epithelial cells had marked ultrastructural evidence of lactation, including protein-containing secretory vesicles, lipid droplets, extensive rough endoplasmic reticulum, and numerous mitochondria. By d 2 of involution, alveolar epithelial cells contained large vacuoles apparently formed by coalescing of protein-containing secretory vesicles and lipid droplets. Large vacuoles were observed in epithelial cells until about the 3rd wk of involution. By d 2 of involution, the Golgi apparatus generally was not apparent. Rough endoplasmic reticulum and mitochondria were observed throughout the period studied, although in reduced amounts compared with their presence in lactating tissue. A marked increase in lysosomal or cytosegresomal structures in epithelial cells was not observed. There was no evidence of extensive sloughing of epithelial cells from the basement membrane. There was a progressive increase in the interalveolar area and a concurrent decrease in the alveolar luminal area as involution progressed. Ultrastructural examination showed that alveolar epithelial cells at d 21 and 30 of involution appear to be functionally active but not secreting milk components.

Animals↗
PubMed1987

Surgical procedure for chronic biliary sample collection in pigs.

To collect biliary samples from pigs, catheters were placed in the distal end of the gallbladders in twelve 20- to 30-kg pigs. An occluder cuff was placed around the bile duct proximal to the duodenum. Inflation of the occluder cuff prevented bile flow into the duodenum and allowed total collection of bile from the catheter in the gallbladder. Deflation of the occluder cuff allowed return of bile flow into the duodenum. Two pigs developed gastric ulcers and two pigs had bile duct dilatation. These responses were attributed to occluder cuffs of inadequate size which could have caused partial or complete obstruction of the bile duct.

Animals↗
PubMed1987

The pig as an animal model for the study of nitrosamine metabolism.

Surgical procedures have been developed that permit the sampling of portal blood, bile and hepatic blood in intact pigs. Animals so prepared have been used to study liver metabolism and biliary excretion of N-nitrosodimethylamine (NDMA) following oral and intravenous dosing.

Animals↗
PubMed1986

Heat shock proteins of vegetative and fruiting Myxococcus xanthus cells.

The heat shock response of Myxococcus xanthus was investigated and characterized. When shifted from 28 to 40 degrees C, log-phase cells rapidly ceased growth, exhibited a 50% reduction in CFU, and initiated the synthesis of heat shock proteins (HTPs). Heat-shocked log-phase M. xanthus cells labeled with [35S]methionine were found to produce 18 major HTPs. The HTPs, analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography, were characterized with regard to molecular mass, subcellular location (periplasm, membrane, or cytoplasm), and temperature required for expression. Most HTPs were expressed at 36 degrees C, the optimum growth temperature of M. xanthus. Cells preincubated at 36 degrees C for 1 h before being shifted to 40 degrees C demonstrated increased thermotolerance compared with cells shifted directly from 28 to 40 degrees C. The HTPs produced by heat-shocked starvation-induced fruiting cells and glycerol-induced sporulating cells were also analyzed and characterized. Thirteen HTPs were detected in fruiting cells shifted from 28 to 40 degrees C. Six of these HTPs were not seen in vegetative M. xanthus cells. Log-phase cells induced to sporulate by the addition of glycerol produced 17 HTPs after being shifted to 40 degrees C. These HTPs were found to be a mixture of HTPs detected in heat-shocked log-phase cells and heat-shocked fruiting cells.

Bacterial Proteins↗
PubMed1986

Effects of feed intake and protein degradability on ruminal characteristics and site of digestion in steers.

Four multiple-fistulated Hereford steers were used in a 4 X 4 Latin square design with a 2 X 2 factorial arrangement of treatments [two intakes (9.1 and 6.1 kg dry matter/d) and two protein sources differing in ruminal degradability (dry distillers grains and dry corn gluten feed)]. Steers fed at the high intake had faster fluid dilution rates (7.63 versus 6.52%/h), higher ruminal fluid outflows (120.2 versus 91.7 L/d), lower apparent ruminal digestibilities of organic matter (41.3 versus 44.3%) and neutral detergent fiber (56.0 versus 60.2%), and lower total tract digestibilities of neutral detergent fiber (64.3 versus 68.7%) than when they were fed at the low intake. Steers fed dry corn gluten feed had higher apparent ruminal digestibilities of organic matter (45.5 versus 40.1%) and neutral detergent fiber (60.2 versus 56.0%) and lower duodenal flows of nonammonia-nonbacterial N (40.1 versus 52.2% of N intake) than when they were fed dry distillers grains. Efficiency of ruminal bacterial growth was higher when steers were fed at the high versus low intakes. Efficiency of ruminal bacterial growth and site and extent of fiber digestion, especially hemicellulose, but not ruminal escape of protein, can be readily altered by manipulation of feed intake of moderately high forage diets.

Ammonia↗