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Biomedical subjects

D R Davis

Publications and source records attributed to D R Davis.

At least 109 records · Page 6Linked to original sources
PubMed1988

Tin-protoporphyrin suppression of hyperbilirubinemia in the jaundiced Gunn rat.

Suppression of hyperbilirubinemia was studied in jaundiced adult and neonatal Gunn rats following treatment with tin-protoporphyrin. The effects of tin-protoporphyrin treatment on heme oxygenase, NADPH cytochrome c reductase, and biliverdin reductase activities were studied in adult jaundiced Gunn rat renal, hepatic and splenic tissues. Hepatic heme oxygenase activity was studied in nonjaundiced and jaundiced Gunn neonates. Significant decreases in plasma bilirubin levels were observed for both adult and neonatal rats treated with 50 or 100 mumol tin-protoporphyrin/kg body weight. Tin-protoporphyrin-treated rats had significantly lower hepatic and renal heme oxygenase activities, splenic and renal cytochrome c reductase activities, and a significantly higher splenic biliverdin reductase activity. Hepatic heme oxygenase activity was also significantly reduced in the neonatal rats.

Aging↗
PubMed1988

Interaction of Malaysian sera with Plasmodium vivax sporozoite antigen.

A seroepidemiologic survey of Plasmodium vivax and Plasmodium falciparum transmission was conducted in 94 Orang Asli children and adults. The prevalence of malaria was 46% in this population, and infections due to P. vivax and P. falciparum occurred with equal frequency. Multi-species infection was common, particularly in children less than 10 years of age. Circumsporozoite (CS) antibodies to P. vivax were detected by ELISA, using the recombinant protein NS181V20, in sera from 53-95% of all subjects in this study. The specificity of reactivity to NS181V20 was confirmed by immunofluorescence using air-dried sporozoites. CS antibodies to P. falciparum were present in less than 50% of the population less than 30 years of age. These data support further testing of this protein as a candidate vivax vaccine.

Adolescent↗
PubMed1988

Increased pro-opiomelanocortin-derived peptide release in myotonic dystrophy.

The response of plasma immunoreactive (IR)-ACTH, IR-beta-endorphin (beta-END) and IR-cortisol to insulin-induced hypoglycaemia, an acute stimulus to the pituitary corticotrophs through the central nervous system, and to synthetic ovine corticotrophin-releasing hormone (CRH), a direct corticotroph stimulator, were studied in normal males and males with myotonic dystrophy. Myotonics had an increased IR-ACTH and IR-beta-END response to hypoglycaemia and an increased IR-ACTH response to CRH compared with normals. Plasma IR-cortisol response were not different in either group of subjects to both stimuli. This neuroendocrine abnormality in myotonic dystrophy may represent a manifestation of the purported specific cell membrane defect underlying the disease. This is the first report of an abnormality in proopiomelanocortin peptide release in myotonic dystrophy.

Adolescent↗
PubMed1987

Isolation and structure elucidation of an epoxide derivative of the hypermodified nucleoside queuosine from Escherichia coli transfer RNA.

A new nucleoside has been identified in tRNATyr from Escherichia coli MRE 600, where it replaces the highly modified nucleoside queuosine. The nucleoside is also present in a large amount relative to queuosine in mixed tRNA from E. coli strains MRE 600 and W (from which it was isolated for characterization). The new nucleoside has been characterized as an epoxy derivative of queuosine: 7-(5-[(2,3-epoxy-4,5-dihydroxycyclopent-1-yl)amino]methyl)-7-de azaguanosine, oQ, based on data from directly combined liquid chromatography/mass spectrometry, high resolution mass spectrometry, and proton NMR spectroscopy. Nucleoside oQ is also present in small amounts in mixed tRNA from E. coli B. Isomerization of oQ occurs readily under alkaline conditions to give a rearranged product, oQ', characterized as 7-(5-[(3,4-epoxy-2,5-dihydroxycyclopent-1-yl)amino]methyl)-7-deaza guanosine. The present finding constitutes the first report of epoxide formation during post-transcriptional processing of RNA.

Chromatography, High Pressure Liquid↗
PubMed1987

Activated charcoal as an adjunct to phototherapy for neonatal jaundice.

The effectiveness of activated charcoal as an adjunct to phototherapy in reducing plasma bilirubin levels was studied in the jaundiced rat. The administration of charcoal either by feeding or gavage was effective in reducing plasma bilirubin levels in both the adult and suckling jaundiced rat. The combination of charcoal feeding and phototherapy in the adult rat was additive in that the bilirubin levels were significantly lower when compared to levels of the rats given charcoal alone. Plasma bilirubin levels were significantly reduced in the suckling jaundiced rat given either charcoal or charcoal together with phototherapy, however, the combination of treatments did not appear to be additive. These data suggest that charcoal could be a useful adjunct to phototherapy by binding bilirubin in the intestinal lumen and reducing the potential for the enterohepatic circulation of unconjugated bilirubin. Charcoal combined with phototherapy may also reduce the intensity of phototherapy needed to effectively lower plasma bilirubin levels.

Animals↗
PubMed1987

Transfer of the heritable nonhemolytic jaundice trait from the Gunn rat to the Sprague-Dawley rat.

Congenital nonhemolytic jaundice as observed in the Gunn rat was transferred successfully to the Sprague-Dawley rat. This jaundice trait occurs as the result of a deficiency of bilirubin glucuronyltransferase and appeared to transfer by simple Mendelian inheritance. A comparison of jaundiced Gunn with jaundiced Gunn-Sprague-Dawley cross rats for plasma bilirubin level, bilirubin glucuronyltransferase activity and female reproductive performance showed no significant difference between the two jaundiced rat groups. The phenotypic expression of the jaundice trait as viewed by the parameters used in this study appeared to be the same for both the Gunn and Gunn-Sprague-Dawley cross rats. The transfer of the jaundice trait to another rat strain enhances the opportunity to characterize this animal model and to determine the possible influence of a long-term closed mating system.

Animals↗
PubMed1986

15N-labeled tRNA. Identification of 4-thiouridine in Escherichia coli tRNASer1 and tRNATyr2 by 1H-15N two-dimensional NMR spectroscopy.

Uridine is uniquely conserved at position 8 in elongator tRNAs and binds to A14 to form a reversed Hoogsteen base pair which folds the dihydrouridine loop back into the core of the L-shaped molecule. On the basis of 1H NMR studies, Hurd and co-workers (Hurd, R. E., Robillard, G. T., and Reid, B. R. (1977) Biochemistry 16, 2095-2100) concluded that the interaction between positions 8 and 14 is absent in Escherichia coli tRNAs with only 3 base pairs in the dihydrouridine stem. We have taken advantage of the unique 15N chemical shift of N3 in thiouridine to identify 1H and 15N resonances for the imino units of S4U8 and s4U9 in E. coli tRNASer1 and tRNATyr2. Model studies with chloroform-soluble derivatives of uridine and 4-thiouridine show that the chemical shifts of the protons in the imino moieties move downfield from 7.9 to 14.4 ppm and from 9.1 to 15.7 ppm, respectively; whereas, the corresponding 15N chemical shifts move downfield from 157.5 to 162.5 ppm and from 175.5 to 180.1 ppm upon hydrogen bonding to 5'-O-acetyl-2',3'-isopropylidene adenosine. The large difference in 15N chemical shifts for U and s4U allows one to unambiguously identify s4U imino resonances by 15N NMR spectroscopy. E. coli tRNASer1 and tRNATyr2 were selectively enriched with 15N at N3 of all uridines and modified uridines. Two-dimensional 1H-15N chemical shift correlation NMR spectroscopy revealed that both tRNAs have resonances with 1H and 15N chemical shifts characteristic of s4UA pairs. The 1H shift is approximately 1 ppm upfield from the typical s4U8 resonance at 14.8 ppm, presumably as a result of local diamagnetic anisotropies. An additional s4U resonance with 1H and 15N shifts typical of interaction of a bound water or a sugar hydroxyl group with s4U9 was discovered in the spectrum of tRNATyr2. Our NMR results for tRNAs with 3-base pair dihydrouridine stems suggest that these molecules have an U8A14 tertiary interaction similar to that found in tRNAs with 4-base pair dihydrouridine stems.

Magnetic Resonance Spectroscopy↗
PubMed1986

15N-labeled tRNA. Identification of dihydrouridine in Escherichia coli tRNAfMet, tRNALys, and tRNAPhe by 1H-15N two-dimensional NMR.

The N3 imino units of dihydrouridine were identified in samples of 15N-labeled Escherichia coli tRNAfMet, tRNALys, and tRNAPhe by 1H-15N two-dimensional NMR. The peaks for dihydrouridine had high field 1H (9.7-9.8 ppm) and 15N (147.8-149.5 ppm) chemical shifts. Assignments were made by 1H-15N chemical shift correlation based on values obtained in model studies with tri-O-benzoyl- and tri-O-acetyldihydrouridine. The rates of exchange of the imino protons with water suggest that the D-loop in tRNAfMet is less stable than the D-loops in tRNALys or tRNAPhe. Closely spaced peaks were observed for the two dihydrouridines in tRNAPhe in a high resolution spectrum.

Escherichia coli↗
PubMed1986

Plasma immunoreactive proopiomelanocortin peptides and cortisol in normal dogs and dogs with Addison's disease and Cushing's syndrome: basal concentrations.

We measured basal plasma concentrations of the immunoreactive (IR) proopiomelanocortin (POMC)-derived peptides ACTH, beta-lipotropin (beta LPH), beta-endorphin (beta END), and alpha MSH in 160 normal dogs, 32 dogs with Addison's disease, 42 dogs with adrenocortical tumors causing Cushing's syndrome, and 169 dogs with pituitary-dependent Cushing's disease. In normal dogs, plasma IR-POMC peptide levels were similar to those in man, except that IR-alpha MSH, a pars intermedia POMC product, was readily detected. In Addisonian dogs, plasma cortisol was decreased, and the IR-POMC peptides were increased, except for IR-alpha MSH, which was normal. In 7 Addisonian dogs given dexamethasone, elevated plasma IR-ACTH, beta LPH, and beta END levels fell dramatically. In dogs with Cushing's syndrome due to adrenal tumors, plasma IR-ACTH, beta LPH, and beta END were decreased, and cortisol was increased, but IR-alpha MSH was normal. Dogs with Cushing's disease due to pars distalis tumors had elevated plasma IR-ACTH, beta LPH, beta END, and cortisol, but normal IR-alpha MSH; their plasma cortisol was suppressed by dexamethasone. There appeared to be 2 types of pars intermedia tumors causing Cushing's disease: 1 dexamethasone nonsuppressible and with disproportionately high plasma IR-alpha MSH levels, the other relatively dexamethasone suppressible and with normal to slightly elevated IR-alpha MSH levels. These 2 pars intermedia tumor types may arise from 2 distinct normal canine pars intermedia cell types. Canine Cushing's disease may provide a useful model for variants of the disorder in man.

Addison Disease↗
PubMed1986

A serological survey of scrub, tick, and endemic typhus in Sabah, East Malaysia.

A seroepidemiological survey of 837 people and 383 febrile patients was performed in rural areas of Sabah. We determined that the rickettsial diseases scrub typhus and endemic typhus were uncommon causes of febrile illness, as was tick typhus, except in forest dwelling peoples. The rate of occurrence of SFGR specific antibody was 16.5% among 412 forest dwellers, indicating that tick typhus may be a frequent cause of illness in this population.

Adolescent↗