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Biomedical subjects

J A Nelson

Publications and source records attributed to J A Nelson.

At least 163 records · Page 9Linked to original sources
PubMed1992

Infant-feeding practices and adiposity in 4-y-old Anglo- and Mexican-Americans.

A longer duration of breast-feeding and later introduction to solids may protect against excessive adiposity in infancy. This study investigated infant feeding practices and their relationship to two measures of adiposity--body mass index (BMI) and sum of skinfold thicknesses (SUMSF)--in 331 4-y-old Anglo- (43%) and Mexican-American (57%) children. No associations were detected between any of the infant feeding variables of duration of breast-feeding and introduction to solids and formula and measures of the child's adiposity. Mother's physical measures of BMI and SUMSF explained the largest portion of variance for both measures of childhood adiposity, BMI (9.5%), and SUMSF (8.3%). Genetic and environmental factors other than infant feeding practices appear to have a greater influence on a 4-y-olds' adiposity.

Adipose Tissue↗
PubMed1992

Spatial analysis of the distribution of Ixodes dammini (Acari: Ixodidae) on white-tailed deer in Ogle County, Illinois.

The pattern of infestations of Ixodes dammini on white-tailed deer in Ogle County in Illinois was studied through examinations of hunted deer from 1988 to 1990. The Illinois Geographic Information System mapped the spatial distribution of tick infestations on deer and related it to a known endemic focus for I. dammini and Borrelia burgdorferi (Castle Rock State Park), and to a major waterway (Rock River). Second-order neighborhood analysis was used to analyze the spatial distribution of deer around Castle Rock State Park. More than 25% of deer were infested. All deer were clustered around CRSP, but the clustering resulted mostly from clustering of infested deer around CRSP. CRSP is apparently the only important source of tick infestations in Ogle County. Clustering of infested deer did not change during the 3-yr study period. The dispersion pattern of ticks on deer was aggregated, with twice and three times as many ticks collected from bucks as from does and from fawns, respectively. More male ticks than female ticks were collected from infested deer. Of 59 ticks removed from harvested deer in 1990, 5.1% tested positive for B. burgdorferi.

Animals↗
PubMed1992

Hepatic contrast-enhancing properties of manganese-mesoporphyrin and manganese-TPPS4. A comparative magnetic resonance imaging study in rats.

OBJECTIVES: Manganese (III) mesoporphyrin (Mn-mesoporphyrin), a synthetic and stable complex, was investigated for its hepatic magnetic resonance imaging (MRI) properties and compared with manganese tetrakis-(4 sulfonatophenyl) porphyrin (Mn-TPPS4). METHODS: Liver abscesses (n = 10) and tumors (n = 14) were induced in rats. These rats then underwent MRI at 2.0 T. Animals received one of the two contrast agents, and measurement of lesion enhancement was performed. RESULTS: At an intravenous dose of 0.035 mmol/kg, Mn-mesoporphyrin caused significant enhancement of normal liver parenchyma and increased the lesion-to-liver contrast in both the models of heptic liver abscess and metastatic liver disease. Mn-TTPS4 at an intravenous dose of 0.04 mmol/kg typically enhanced both lesion and normal liver parenchyma and therefore did not improve the lesion-to-liver contrast. CONCLUSIONS: The hepatotrophic properties of Mn-mesoporphyrin indicate its potential as an intravenous contrast agent for liver imaging.

Animals↗
PubMed1992

Consequences of 6-thioguanine incorporation into DNA on polymerase, ligase, and endonuclease reactions.

The incorporation of 6-thioguanine (S6G) in place of guanine proceeds readily in DNA synthesis reactions catalyzed by mammalian and bacterial polymerases. This report summarizes the consequences of such incorporation studied to date. S6G was incorporated into one strand of a defined M13mp18 phage sequence in a (+)reaction catalyzed by the Klenow fragment of Escherichia coli DNA polymerase I. After denaturation of the newly synthesized strand (containing S6G) and annealing with a reverse (-) 32P-labeled primer, polymerization catalyzed by the Klenow enzyme as well as by human DNA polymerases alpha, gamma, and delta was slowed considerably, compared with that across the corresponding guanine-containing template. To evaluate S6G-containing DNA as a substrate for DNA ligases, two oligodeoxynucleotides (19- and 20-mers) antisense to a 40-mer were synthesized so that the 40-mer coded for guanine at the 3' terminus of the 19-mer. After annealing of the synthetic oligonucleotides to form a duplex DNA containing a one-nucleotide gap (opposite cytosine in the 40-mer), the 19-mer was extended with 2'-deoxythioguanosine 5'-triphosphate using DNA polymerase, forming a nicked duplex DNA. The abilities of T4 DNA ligase and HeLa and calf thymus DNA ligase I to join the 5'-phosphate with the 3'-S6G-OH were severely inhibited, compared with the 3'-guanine-extended control. This finding suggests that incorporation of S6G at the 3' terminus of Okazaki fragments would inhibit lagging strand DNA synthesis. In other experiments, cleavage of S6G-containing DNA by some but not all restriction endonucleases progressed poorly, compared with the control guanine-containing DNA, independently of the location of S6G at recognition or cleavage sites, as previously observed by Iwaniec et al. [Mol. Pharmacol. 39:299-306 (1991)] with a different spectrum of enzymes. These findings indicate altered DNA-protein interactions due to S6G incorporation. The poor template function of S6G-containing DNA is consistent with the known delayed cytotoxicity and DNA damage previously reported to occur in S6G-treated cells.

Autoradiography↗
PubMed1992

Postnatal development of organic cation transport and mdr gene expression in mouse kidney.

The apical surface of the proximal tubular epithelium is the site of both P-glycoprotein localization and postulated active secretion of organic cations in the mammalian kidney. P-glycoprotein has been shown to act as a pleiotropic drug efflux pump across the cell membrane of tumor cells expressing the multidrug resistance phenotype, whereas the renal organic anion and organic cation secretory systems serve the function of pleiotropic drug transport across the proximal tubule epithelium. Because most known substrates for P-glycoprotein are organic cations, we tested the hypothesis that the physiological function of this protein in the kidney is to mediate renal organic cation secretion. In one approach, we compared the postnatal development of organic cation transport with that of kidney mdr gene expression. Cimetidine-sensitive uptake of classical substrates for renal secretion (N-methyl nicotinamide and tetraethylammonium) into kidney slices developed gradually in neonate mice, reaching adult capacity in 4 to 6 weeks. P-glycoprotein and its mRNA, as estimated by immunohistochemical methods and RNAse protection analysis, were undetectable at birth and were expressed abruptly at the adult level between 2 and 3 weeks of age. In another approach, classical inhibitors of renal organic cation secretion (cimetidine and cyanine 863) failed to reverse resistance to adriamycin in Chinese hamster ovary and P388 cell lines, which possess the phenotypic traits of multidrug resistance. These results suggest that the cimetidine-sensitive component of organic cation secretion is mediated by a protein other than the P-glycoprotein in the mammalian kidney.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

The composite resin-amalgam window preparation.

Amalgam restorations with a very visible mesiofacial aspect can be aesthetically modified. Clinical experience has proven the amalgam window preparation to be an economical, expedient, and effective treatment approach when patients request tooth-colored fillings in posterior maxillary teeth.

Composite Resins↗
PubMed1992

Anglo- and Mexican-American preschoolers at home and at recess: activity patterns and environmental influences.

Habitual physical activity in children is related to physical fitness and appears to mediate cardiovascular disease (CVD) risk factors. We studied the physical activity patterns and associated variables of a large bi-ethnic cohort of 4-year-old children from low to middle socioeconomic families. Trained observers coded the behavior of 351 children (150 Anglo-American, 201 Mexican-American; 182 boys, 169 girls) during two 60-minute home visits and two unstructured recesses lasting up to 30 minutes each at 63 different preschools. Findings indicated that although children were much less active at home, there were low but significant correlations between their activity patterns at home and during recess (r = .13). Children who had activity-promoting toys at home also tended to have them available during preschool recess (r = .20). Ethnic differences were evident for both activity and environmental variables. Mexican-American children were less active than Anglo children at home (p less than .002) and during recess (p less than .03), thus adding to the adult literature that has found Mexican-Americans to be less active than Anglos, and supporting to the notion that physical activity life-style habits may be established in early childhood. In both settings, Mexican-American children spent more time in presence of adults (home, p less than .04; recess, p less than .03) and had access to fewer active toys (home, p less than .001; recess, p less than .05). Gender differences were also evident for both activity and environmental variables.(ABSTRACT TRUNCATED AT 250 WORDS)

California↗
PubMed1991

Porphyrins as contrast media.

The interest in tissue distribution of variously labeled or otherwise detectable natural and synthetic porphyrins and porphyrin derivatives dates back well over 60 years. Although a considerable interest in fluorescent tumor localization and therapy dominates the history of porphyrin biodistribution studies, many investigators have evaluated the diagnostic and therapeutic characteristics of porphyrins with radioactive, radiopaque, and paramagnetic qualities. In this paper, a review of the use of porphyrins as nuclear medicine, X-ray, and NMR contrast agents is presented.

Animals↗
PubMed1991

Intrathoracic airstream temperatures during acute expansions of thoracic blood volume.

1. To determine the validity of employing intrathoracic heat flux as a reflection of changes in bronchial blood flow, we used a thermal probe to record airstream temperatures within the tracheobronchial tree in five normal and five asthmatic subjects during isocapnic hyperventilation challenges with and without inflation of the lower limb bladders of a pressure suit. 2. During hyperpnoea, airstream temperatures fell progressively in both subject groups. When blood volume was acutely shifted from the legs into the thorax via anti-shock trousers, airstream temperatures within the tracheobronchial tree rose and were significantly higher than the temperature recorded during hyperpnoea alone. In the normal subjects, once hyperpnoea ceased, the rate of airway re-warming was similar whether or not the anti-shock trousers were inflated. In the asthmatic subjects, however, shifting blood into the thorax attenuated the obstructive response to hyperpnoea and slowed the rate of re-warming. 3. These data demonstrate that changes in airway blood volume are reflected in fluctuations in intrathoracic heat exchange and that disruption of the end hyperpnoea thermal gradient attenuates the airway obstruction that follows hyperpnoea. Since the bronchial blood supply is the major source of heat to the airways, this circulation may play an important role in thermally induced asthma.

Asthma↗
PubMed1991

Improved method for in vivo magnetic resonance contrast media research.

This paper describes an approach for contrast media research with which high resolution MR images of rats can be studied before, during, and after intravenous contrast media administration. Using a probe designed to hold up to eight rats, the contrast-enhancing properties in normal rat brains of Gd-DTPA, a low molecular weight compound, and polylysine-(Gd-DTPA), a high molecular weight compound, were compared simultaneously in two groups of four rats each. Signal intensity-time graphs, as measured over various anatomical structures of the normal rat head, demonstrated the feasibility of directly comparing enhancement patterns of two pharmacologically different contrast agents and obtaining relevant data in a single experiment.

Animals↗
PubMed1991

Differentiation induction of human promyelocytic leukemia cells by 10-hydroxycamptothecin, a DNA topoisomerase I inhibitor.

The cytotoxic and differentiating effects of 10-hydroxycamptothecin (HCPT) in the human promyelocytic leukemia cell line HL-60 were examined. By trypan blue dye exclusion, a 24-h exposure of the cells to 0.1 microM of the drug was found to be cytotoxic. Exposure of the cells to lower concentrations (0.001-0.01 microM) for 3 days reduced cell proliferation and induced cell differentiation. As determined by Wright-Giemsa staining, approximately 25% of promyelocytic cells became metamyelocytes, banded and segmented neutrophils. Electron microscopy demonstrated alterations in the ultrastructure of HCPT-induced HL-60 cells that included the formation of lobulated nuclei and the accumulation of large vesicles and small myelin bodies as well as glycogen-like particles in the cell periphery. Qualitatively similar results were obtained in a subline of HL-60 that is resistant to 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA); however, the rate and extent of induced nitroblue tetrazolium-positive cells by HCPT and several other agents were greater in the resistant cell line. Under conditions that induced cell differentiation, HCPT sharply inhibited [3H]thymidine incorporation into DNA and increased the rate of protein synthesis without an effect on the rate of RNA synthesis. The measurement of DNA topoisomerase I activity in nuclear extracts from both HCPT- and DMSO-treated cells demonstrated that the enzyme was decreased in mature cells compared to nondifferentiated controls. The data suggest that progressive reduction of DNA topoisomerase I activity may be associated with cell differentiation, but whether HCPT-induced differentiation is mediated by inhibition of the enzyme is inconclusive.

Antineoplastic Agents, Phytogenic↗
PubMed1991

Pathogenesis of HIV encephalitis.

A wide spectrum of infectious agents attack the central nervous system (CNS) of acquired immunodeficiency syndrome (AIDS) patients. Human immunodeficiency virus (HIV) itself, infects the CNS of a subgroup of these patients. The mechanism behind why HIV enters the CNS is unclear. We have observed an interesting association between HIV and opportunistic viral infections that may explain why HIV enters the brain. Infection of the CNS by opportunistic agents results in recruitment of latently HIV-infected monocytes. Upon differentiation into macrophages these cells produce abundant HIV. Latent HIV-infection of monocytes/macrophages provides a unique opportunity for cooperativity between opportunistic infections and HIV in mediating CNS damage.

AIDS Dementia Complex↗
PubMed1991

A national survey on pediatric training and activities in school health.

National trends in school health practice and training were assessed 10 years after the report of the 1978 American Academy of Pediatrics Task Force on Pediatric Education. A questionnaire was sent to 2,237 randomly selected AAP Fellows and was returned by 1,068 (48%). Seventy-seven percent of practicing pediatricians reported involvement in some type of school-based or school consultant activity. Those having residency training in school health and those practicing in rural areas were most likely to be involved. The most common types of activity were school-based pre-athletic exams (56%), consultant to special education placement (26%), and game/event physician (23%). Pediatricians were paid for 20% of sports-related school consultation and 25% of nonsports school health activities. Didactic or clinical training in school health was offered during residency to 19%. Specific didactic topics in school health included learning and attention deficit disorders (32%), physician role in health education (15%), and sports medicine (12%). Preathletic participation exams were the most commonly performed school health activity during residency (23%), followed by serving as a school consultant (11%), and attending an individual education plan meeting (7%). Most pediatricians engaged in school health activities. However, they did so without preparation during residency and without payment for their services.

Chi-Square Distribution↗