Search PubMed⌕ Search

Biomedical subjects

T Nelson

Publications and source records attributed to T Nelson.

At least 91 records · Page 5Linked to original sources
PubMed1984

2-Deoxyglucose incorporation into rat brain glycogen during measurement of local cerebral glucose utilization by the 2-deoxyglucose method.

The incorporation of 14C into glycogen in rat brain has been measured under the same conditions that exist during the measurement of local cerebral glucose utilization by the autoradiographic 2-[14C]deoxyglucose method. The results demonstrate that approximately 2% of the total 14C in brain 45 min after the pulse of 2-[14C]deoxyglucose is contained in the glycogen portion, and, in fact, incorporated into alpha-1-4 and alpha-1-6 deoxyglucosyl linkages. When the brain is removed by dissection, as is routinely done in the course of the procedure of the 2-[14C]deoxyglucose method to preserve the structure of the brain for autoradiography, the portion of total brain 14C contained in glycogen falls to less than 1%, presumably because of postmortem glycogenolysis which restores much of the label to deoxyglucose-phosphates. In any case, the incorporation of the 14C into glycogen is of no consequence to the validity of the autoradiographic deoxyglucose method, not because of its small magnitude, but because 2-[14C]deoxyglucose is incorporated into glycogen via [14C]deoxyglucose-6-phosphate, and the label in glycogen represents, therefore, an additional "trapped" product of deoxyglucose phosphorylation by hexokinase. With the autoradiographic 2-[14C]deoxyglucose method, in which only total 14C concentration in the brain tissue is measured by quantitative autoradiography, it is essential that all the labeled products derived directly or indirectly from [14C]deoxyglucose phosphorylation by hexokinase be retained in the tissue; their chemical identity is of no significance.

Animals↗
PubMed1983

Naloxone pretreatment alters the local cerebral metabolic effect of gamma-hydroxybutyrate in rats.

The effect of naloxone on gamma-hydroxybutyrate (GHB)-induced cerebral metabolic depression was studied in rats with the 2-[14C]deoxyglucose method. Naloxone pretreatment statistically significantly antagonized the cerebral metabolic effect of GHB in 10 of 38 structures examined. These results are consistent with previous data showing reversal of the dopaminergic, electroencephalographic, and behavioral effects of GHB by naloxone and suggest that some of the neuropharmacological effects of GHB are mediated by the endogenous opiate system.

Animals↗
PubMed1983

Radionuclide analysis of pulmonary blood volume: the response to spontaneous angina pectoris and sublingual nitroglycerin in patients with coronary artery disease.

By manually assigning pulmonary regions of interest and deriving pulmonary time-activity (volume) curves, we were able to make count estimates of pulmonary blood volume (PBV) from gated cardiac blood pool scans. Five patients with coronary heart disease developed angina spontaneously while under a gamma camera. This produced an increase in cardiac volumes (p less than 0.05), a reduction in left ventricular ejection fraction (p less than 0.01), along with a marked increase in PBV (0.010 +/- 0.003 to 0.015 +/- 0.002 units, p less than 0.05). Nitroglycerin was then administered and reduced PBV in association with a return to normal in cardiac systolic function and size. In patients with stable chronic ischemic heart disease, sublingual nitroglycerin also reduced PBV (p less than 0.05), although not as much as when administered during an anginal episode. We conclude that gated imaging of the chest can be utilized to follow changes in PBV serially. These changes can be utilized to evaluate clinically important changes in hemodynamic status and the response to pharmacologic interventions.

Adult↗
PubMed1983

Regulation and properties of an NADP+ oxidoreductase which functions as a gamma-hydroxybutyrate dehydrogenase.

A number of naturally occurring biological intermediates have been found to inhibit competitively the activity of a highly purified NADP+-dependent oxidoreductase which catalyzes the simultaneous oxidation of gamma-hydroxybutyrate to succinic semialdehyde, and the reduction of D-glucuronate to L-gulonate. Of the inhibitors studied, those with the lowest Ki are the alpha-keto analogues of the branched chain or aromatic amino acids. The Vmax and Km for this enzyme are affected by pH; consequently, changes in substrate concentration can markedly alter the pH optimum. The enzyme has been found to be inhibited by reducing agents such as dithiothreitol and mercaptoethanol, protected against this inhibition by oxidizing agents such as oxidized glutathione or H2O2, and finally, protected against heat inactivation by the presence of either NADP+ or NADPH.

Animals↗
PubMed1982

Mitomycin C: phase I study of a constant infusion ambulatory treatment schedule.

Thirty patients received mitomycin C by constant infusion for 5 consecutive days (16 patients ) or for extended period by an ambulatory infusion pump (Cor-Med model) for 9 to 30 days (14 patients). The short-term 5-day infusions were delivered at dose rates of 2, 3, 4, 5 and 6 mg/m2/d with a cumulative dose of 15-50 mg. The protracted infusions were delivered at dose rates of 0.75-3 mg/m2/d with a cumulative dose of 21.6-65.2 mg. Marrow suppression was dose-limiting and occurred in 5/6 evaluable patients receiving more than 30 mg in the short-term infusion schedule and 8/10 evaluable patients receiving more than 20 mg in the protracted infusion schedule. The characteristics of the marrow suppression are that: a) thrombocytopenia precedes or is observed without concomitant leukopenia and b) the nadir day is delayed (WBC day 42, platelet day 36). Mitomycin C delivered by constant infusion leads to dose-limiting marrow toxicity at 20 to 30 mg cumulative dose depending upon the dose rate and duration of treatment. For short-term 5-day therapy, 3 mg/m2/d and for protracted therapy (up to 30 d) 0.75 mg/m2/d are the recommended dose rates for the constant infusion schedule.

Adult↗
PubMed1981

Kinetics of coupled gamma-hydroxybutyrate oxidation and D-glucuronate reduction by an NADP+-dependent oxidoreductase.

A highly purified NADP+-dependent oxidoreductase from hamster liver (1) has been found to catalyze a reaction in which the oxidation of gamma-hydroxybutyrate is coupled to the reduction of D-glucuronate. In the coupled reaction, NADP+ is required in catalytic rather than stoichiometric amounts. When the coupled reaction is carried out under limiting conditions for the oxidation of gamma-hydroxybutyrate (i.e. a very low concentration of NADP+ and an inhibitory concentration of NADPH) the rate of gamma-hydroxybutyrate oxidation is determined by the concentration of D-glucuronate and can be stimulated at least 8-fold by D-glucuronate. The kinetics of the oxidation of gamma-hydroxybutyrate have been studied in both the uncoupled and the coupled reaction. In the coupled reaction the reduction of D-glucuronate drives the oxidation of gamma-hydroxybutyrate; the Km for NADP+ is markedly lower than the Km determined in the uncoupled reaction (1.4 X 10(-6) M as compared to 2 X 10(-5) M), and the inhibition by NADPH can be completely overcome. The kinetics of the uncoupled reaction suggest that, unlike many other dehydrogenases, the oxidation of gamma-hydroxybutyrate catalyzed by this enzyme proceeds by a Rapid Equilibrium Random Bi Bi mechanism.

Animals↗
PubMed1981

Ribonucleic acid and other polyanions facilitate chromatin assembly in vitro.

Crude extracts of Drosophila embryos are a rich source of both DNA topoisomerase I and chromatin assembly activity [Nelson, T., Hsieh, T., & Brutlag, D.L. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 5510-5514; Hseih, T., & Brutlag, D. L. (1980) Cell (Cambridge, Mass.) 21, 115-125]. Purified topoisomerase I from Drosophila embryos, however, is not sufficient for chromatin assembly. Rather, the ability of Drosophila embryo extracts to mediate chromatin assembly in vitro requires an anionic fraction which we demonstrate to be RNA. Exogenous natural and homopolymer RNAs, if of sufficient length, can also mediate chromatin assembly in vitro. The RNA acts stoichiometrically in assembly, being required in amounts at least equal in weight to the amount of histones present. Natural and homopolymer DNAs, whether single or double stranded, are inactive under the same conditions. The arginine-rich histones H3 and H4 or histone H4 alone is sufficient to produce nucleoprotein complexes with physiological numbers of supertwists in the DNA. Complexes containing these subsets of the core histones also resemble assembled complexes containing all four core histones with respect to some patterns of nuclease sensitivity, although complexes containing all four core histones more closely resemble native chromatin in nuclease digestions.

Animals↗
PubMed1981

The extraneural distribution of gamma-hydroxybutyrate.

gamma-Hydroxybutyrate has been found to be widely distributed in both neural and extraneural tissues in the rat. The kidney and brown fat have more than 10 times higher concentrations of gamma-hydroxybutyrate than does the brain. This observation suggests that gamma-hydroxybutyrate may participate in the metabolism of many organs, and that GABA may not be the precursor in extraneural tissues.

3-Hydroxybutyric Acid↗
PubMed1979

Extracts of Drosophila embryos mediate chromatin assembly in vitro.

Extracts of Drosophila embryos can mediate the assembly of a chromatinlike structure from histones and DNA under physiological conditions. The histone-DNA complex formed in vitro contains micrococcal nuclease-sensitive sites spaced at 200-base pair intervals. More extensive digestion of the complex by micrococcal nuclease generates 11S particles which cosediment with nucleosome core particles isolated from native chromatin. These particles contain 140-base pair DNA fragments which upon further cleavage with micrococcal nuclease give rise to a pattern of discretely sized DNA fragments characteristic of nucleosome core particles. We have assayed the chromatin assembly process both qualitatively by measuring the induction of supertwists into a relaxed circular DNA (a process requiring a nicking-closing enzyme) and quantitatively by measuring the formation of micrococcal nuclease-resistant DNA fragments from radioactively labeled linear DNA. The amount of chromatin formed depends primarily on the amount of histones, whereas the rate of assembly depends on the amount of extract protein added. The factors in the extract that mediate chromatin assembly appear to interact first with the DNA because preincubation of the DNA with the extract markedly increases the extent of assembly.

Animals↗
PubMed1979

Effects of maximal exercise stress on left ventricular function in patients with coronary artery disease using first pass radionuclide angiocardiography: a rapid, noninvasive technique for determining ejection fraction and segmental wall motion.

Angiographically determined changes in segmental wall motion (SWM) and ejection fraction (EF) are sensitive indices of left ventricular (LV) function. To compare the effects of exercise on LV function, first pass radionuclide angiocardiography was used before and during maximal upright bicycle stress in patients with nonsignificantly stenosed coronary arteries, and in those with greater than 75% stenosis. Gamma camera acquisitions were made in the 30 degree RAO projection using a 20 mCi I.V. bolus of 99mTc-pertechnetate. In the control group (seven normals, one nonsignificant (CAD) the EF significantly increased between rest and exercise (0.65 +/- 0.03 to 0.81 +/- 0.03 (mean +/- SEM), p less than 0.005). In this group SWM measured over the two anterior and two inferoposterior segments uniformly increased. In the 11 patients with a history of angina and significant coronary artery obstruction, the EF did not change in three and significantly decreased in the remaining eight (0.57 +/- 0.04 to 0.45 +/- 0.03, p less than 0.005). In all 11 patients SWM either decreased or did not increase in the areas supplied by the significantly stenosed coronary arteries. Upright maximal stress angiocardiography appears to be well-suited for diagnosing ischemic heart disease and localizing the area of ischemic dysfunction.

Adult↗
PubMed1977

Synthesis of hybrid bacterial plasmids containing highly repeated satellite DNA.

Hybrid plasmid molecules containing tandemly repeated Drosophila satellite DNA were constructed using a modification of the (dA)-(dT) homopolymer procedure of Lobban and Kaiser (1973). Recombinant plasmids recovered after transformation of recA bacteria contained 10% of the amount of satellite DNA present in the transforming molecules. The cloned plasmids were not homogenous in size. Recombinant plasmids isolated from a single colony contained populations of circular molecules which varied both in the length of the satellite region and in the poly(dA)-(dt) regions linking satellite and vector. While subcloning reduced the heterogeneity of these plasmid populations, continued cell growth caused further variations in the size of the repeated regions. Two different simple sequence satellites of Drosophila melanogaster (1.672 and 1.705 g/cm3) were unstable in both recA and recBC hosts and in both pSC101 and pCR1 vectors. We propose that this recA-independent instability of tandemly repeated sequences is due to unequal intramolecular recombination events in replicating DNA molecules, a mechanism analogous to sister chromatid exchange in eucaryotes.

DNA↗