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J K Saunders

Publications and source records attributed to J K Saunders.

53 records · Page 3Linked to original sources
PubMed1991

The effects of caffeine on ischemic neuronal injury as determined by magnetic resonance imaging and histopathology.

The effects of caffeine on ischemic neuronal injury were determined in rats subjected to forebrain ischemia induced by bilateral carotid occlusion and controlled hypotension (50 mmHg for 10 min). High resolution (100 microns) multi-slice, multi-echo magnetic resonance images were obtained daily for three consecutive days post-operatively in sham-operated rats and in rats that received either saline vehicle (controls), a single i.v. injection of 10 mg/kg caffeine 30 min prior to an ischemic insult (acute caffeine group), or up to 90 mg/kg per day of caffeine for three consecutive weeks prior to an ischemic insult (chronic caffeine group). Rats in the control group exhibited enhanced magnetic resonance image intensity in the striatum 24 h after ischemia which increased in the striatum and also appeared in the hippocampus after 48 h, and which began to resolve in both regions by 72 h post-ischemia. Histopathological analysis of each rat following the final magnetic resonance examination showed that ischemic neuronal injury was strictly confined to the brain regions showing magnetic resonance image changes. Acute caffeine rats showed accelerated changes in the magnetic resonance images, with increased hippocampal intensity appearing at 24 h post-ischemia. Although there was magnetic resonance evidence of accelerated injury, quantitative analysis of the histopathological data at 72 h showed no significant difference in the extent of neuronal injury in any brain region between control-ischemic and acute caffeine rats. Nine out of 11 rats in the chronic caffeine group showed no magnetic resonance image changes over the three study days. Chronic caffeine rats had significantly less neuronal damage in all vulnerable brain regions than either of the other groups of ischemic rats. The accelerated ischemic injury in rats treated with an acute dose of caffeine may occur secondary to antagonism of adenosine receptors, whereas protection from ischemic injury following chronic administration of caffeine may be mediated by up-regulation of adenosine receptors.

Adenosine↗
PubMed1991

23Na and flame photometric studies of the NMR visibility of sodium in rat muscle.

23Na nuclear magnetic resonance spectroscopy (NMR) is increasingly being used to study Na+ gradients and fluxes in biological tissues. However, the quantitative aspects of 23Na NMR applied to living systems remain controversial. This paper compares sodium concentrations determined by 23Na NMR in intact rat hindlimb (n = 8) and excised rat gastrocnemius muscle (n = 4) with those obtained by flame photometric methods. In both types of samples, 90% of the sodium measured by flame photometry was found to be NMR-visible. This is much higher than previously reported values. The NMR measurements for intact hindlimb correlated linearly with the flame photometric measurements, implying that one pool of sodium, predominantly extracellular, is 100% visible. From measurements on excised muscle, in which extracellular space is more clearly defined, the NMR visibility of intracellular Na+ was calculated to be 70%, assuming an extracellular space of 12% of the total tissue water volume and an extracellular NMR visibility of 100%. 23Na transverse relaxation measurements were carried out using a Hahn spin echo on both intact hindlimb (n = 1) and excised muscle (n = 2) samples. These showed relaxation curves that could each be described adequately using two relaxation times. The rapidly relaxing component showed a T2 value of 3-4 ms and the slowly relaxing component a T2 of 21-37 ms. A spin lattice relaxation (T1) measurement on intact hindlimb yielded a value of 51 ms. These relatively long relaxation times show that the quadrupolar relaxation effect of Na+ complexing to large macromolecules or being otherwise motionally restricted is relatively weak. This is consistent with the high NMR visibilities reported here.

Animals↗
PubMed1990

Optimization of magnetization transfer measurements: statistical analysis by stochastic simulation. Application to creatine kinase kinetics.

A systematic study was performed to optimize the accuracy of kinetic parameters derived from magnetization transfer measurements. Three techniques were investigated: time-dependent saturation transfer (TDST), saturation recovery (SRS), and inversion recovery (IRS). In the last two methods, one of the resonances undergoing exchange is saturated throughout the experiment. The three techniques were compared with respect to the accuracy of the kinetic parameters derived from experiments performed in a given, fixed, amount of time. Stochastic simulation of magnetization transfer experiments was performed to optimize experimental design. General formulas for the relative accuracies of the unidirectional rate constant (k) were derived for each of the three experimental methods. It was calculated that for k values between 0.1 and 1.0 s-1, T1 values between 1 and 10 s, and relaxation delays appropriate for the creatine kinase reaction, the SRS method yields more accurate values of k than does the IRS method. The TDST method is more accurate than the SRS method for reactions where T1 is long and k is large, within the range of k and T1 values examined. Experimental verification of the method was carried out on a solution in which the forward (PCr----ATP) rate constant (kf) of the creatine kinase reaction was measured.

Adenosine Diphosphate↗
PubMed1990

Magnetic resonance spectroscopy in cancer research.

Magnetic resonance spectroscopy (MRS), a useful complement to magnetic resonance imaging (MRI), yields a wealth of information about the biochemical content of tissue and the dynamic behavior of its component molecules. When used for colonic tumors, it can distinguish between those with and those without metastatic potential, through the relaxation time (T2) of the resonance at 1.3 ppm in the proton (1H) MRS spectrum. The presence of peaks near 3.2 ppm correlates well with tumor stage and allows identification of premalignant tissue. Two-dimensional MRS provides an independent method for staging colonic tumors by means of a crosspeak between 1.3 and 4.2 ppm. With a combination of MRS and MRI (localized spectroscopy) it should soon be possible to locate and stage a colonic tumor without physical intervention. In the plasma of patients who have cancer there often exists a lipoprotein band with MRS characteristics similar to those of colonic tumors. It also occurs occasionally in healthy persons and in those who have diseases other than cancer. The lipoprotein appears to be lipoprotein (a), which also has been associated with cardiac disease. We have used a simple MRS measurement on unfractionated plasma, which has been suggested as a reliable indicator of the presence of cancer, on approximately 1800 persons who were healthy, ill with cancer, and ill with other diseases. We found it unsatisfactory as a screening method for an asymptomatic population, because essentially it measures the plasma triglyceride level, especially that in very low-density lipoprotein, which can be elevated for a variety of reasons unrelated to cancer.

Animals↗
PubMed1989

Forebrain ischemia studied using magnetic resonance imaging and spectroscopy.

A combination of magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) has been used to follow the time course of changes resulting from forebrain ischemia in the rat. The 31P MRS demonstrates that the level of high energy metabolites decreases significantly during the 10 min ischemic period but returns to normal after 1 h of reperfusion. MRI shows no change after 1 h of reperfusion but significant changes in the striatum after 24 h and in the hippocampus after 48 h. These changes correlate well with histopathology. Diabetic rats have shown the effect of hyperglycemia in accentuation of ischemic and post ischemic pH changes. Conversely, diabetic rats maintained severely hypoglycemic with insulin showed little variation in pH during or following the ischemic insult. The results emphasize the importance of both MRS and MRI in following the temporal profile and distribution of ischemic neuronal injury.

Animals↗
PubMed1989

31P NMR studies of the metabolic status of pig hearts preserved for transplantation.

31P NMR spectroscopy has been used to evaluate the metabolic status of cardioplegically arrested pig hearts. Hearts were stored with Plegisol for up to 12 hours at either 5 degrees C or 12 degrees C. Results indicated that the ATP content of hearts could be maintained (greater than 70% of initial values) for up to 5 hours in the ischemic storage state. The ATP loss was greater at 12 degrees C. PCr was lost exponentially under the same conditions. Functional testing by reperfusing the stored hearts in vitro indicated a good correlation between the ATP content and survivability of the preparations. Twenty-four hour preservation of pig hearts using slow perfusion with a modified cardioplegic solution (Wicomb) allowed for preservation of both PCr and ATP, in all cases, reperfusion of hearts revealed a loss of NMR- visible ATP and PCr.

Adenosine Triphosphate↗
PubMed1989

Preservation of high-energy phosphates in human myocardium. A phosphorus 31-nuclear magnetic resonance study of the effect of temperature on atrial appendages.

After prolonged exposure to low temperatures (1 degree and 4 degrees C), human atrial trabeculae show poor recovery of contraction. At somewhat higher temperatures (12 degrees and 20 degrees C), recovery is much better (Keon and associates. Ann Thorac Surg 1988;46:337-41). Although better preservation of adenosine triphosphate and therefore improved contractile recovery might be expected after exposure to lower temperatures, it remained possible that, below a certain temperature, adenosine triphosphate-generating mechanisms could be slowed more than adenosine triphosphate utilization. To investigate this phenomenon further, we followed the time course of metabolic changes in human atrial appendages, harvested during cardiac bypass operations, at 1 degree, 4 degrees, 12 degrees, and 20 degrees C using high-resolution 31P and 1H nuclear magnetic resonance spectroscopy. The results are quantitated by correlation with data obtained from biochemical assays on quick-frozen tissues. Initial adenosine triphosphate levels in myocytes of human atrial appendages are 3.3 to 4.3 mumol.gm-1 tissue wet weight. At 20 degrees C, adenosine triphosphate disappears after 6 hours; at 12 degrees C, about half the initial adenosine triphosphate is still observable at this time; at 4 degrees C or 1 degree C, the decline is still slower. Only a small contribution toward adenosine triphosphate maintenance comes from creatine phosphate, since creatine phosphate, inorganic phosphate, and total creatine levels in the appendage are low (less than 2 mumol.gm-1 tissue wet weight). Glycolysis is active at all temperatures; the rate of glycolysis correlates positively with increasing temperature. Adenosine triphosphate generated by glycolysis falls just short of demand at all temperatures, but the difference is small at 1 degree and 4 degrees C. These studies lead us to conclude that the relatively poor recovery of contractile response of human atrial trabeculae, together with contracture reported previously at lower temperatures (1 degree and 4 degrees C), is not due to a failure to maintain adenosine triphosphate levels.

Adenosine Triphosphate↗
PubMed1988

Application of a T2-filtered COSY experiment to identify the origin of slowly relaxing species in normal and malignant tissue.

The 1H NMR spectrum of whole cells consists of many overlapping resonances which are difficult to resolve into individual components. We have developed a modification of the COSY pulse sequence which filters out resonances on the basis of their T2 relaxation rate. When applied to malignant cells, this technique has helped to identify fucose as the origin of the slowly relaxing species associated with their metastatic capacity. The technique can also be used to obtain T2 relaxation rates for individual resonances in a broad envelope of lines.

Adipose Tissue↗
PubMed1988

1H and 13C NMR studies of tissue from normal and diseased mice. Analysis of T1 and T2 relaxation profiles of triglycerides in liver.

The study was initiated to gain a better understanding of the manifestation of disease in the lipid dynamics in tissue. We have performed high resolution 13C and 1H NMR relaxation measurements on the observable lipid resonances in liver and adipose tissue, excised from mice which were normal fed, normal fasted, and infected with the malarial parasite Plasmodium berghei. We have observed that, although the parasite does not invade the hepatocytes, the composition of the liver lipids changes along with nutritional status and disease state. Analysis of the liver lipids using gas chromatography showed that in all cases studied (normal or malarial, fed or fasted) the phospholipid content of the liver remains constant. The triglyceride content, however, shows an increase of up to fourfold in both 24-hour fasted controls and highly parasitized mice. The fatty acid compositions of the triglycerides in 24-hour fasted normal and highly parasitized mice are altered, when compared with fed controls or with mice having a low level of infection. The unsaturation index increases twofold. The 13C T1 experiments on the methylene and olefinic resonances of liver give a single exponential decay. The value for a particular carbon is independent of the origin of the tissue, the nutritional status or the disease state of the animal. In contrast, both 1H and 13C T2 relaxation of the methylene and olefinic carbon resonances can generally be best analyzed as the sum of two exponential decays (based on an F-test). The 13C T2 values and the pre-exponential weighting factors are independent of the origin of the tissue examined. The T2 data could also be analyzed in terms of a distribution of relaxation times, a physically more realistic model. Lastly, our results suggest that the 1H and 13C resonances of lipids in the cells of diseased or normal liver tissues do not give rise to "long" T2 values, as have been observed in cancer cells with metastatic potential.

Animals↗
PubMed1987

Solvent influence on model oxidations of alpha-tocopherol.

(+/-)-alpha-Tocopherol has been oxidised with t-butyl hydroperoxide in chloroform in order to simulate in vivo oxidations due to lipid hydroperoxides. t-Butyl hydroperoxide proved to be a weak oxidant and failed to oxidise alpha-tocopherol in 3 h at 60 degrees C. Inclusion of a small amount of ethanol in the reaction mixture brought about immediate oxidation and the formation of a new product, 5-ethoxymethyl-7,8-dimethyltocol in addition to the spiro dimer and spiro trimer of alpha-tocopherol, alpha-tocopherylquinone and 5-formyl-7,8-dimethyltocol. Formation of 5-ethoxymethyl-7,8-dimethyltocol increased with increasing concentrations of ethanol, up to a maximum of 59% at 20% ethanol. Further increase in ethanol concentration brought about a decrease in the oxidation of alpha-tocopherol and in the formation of 5-ethoxymethyl-7,8-dimethyltocol. Oxidation of the tocopherol model compound 2,2,5,7,8-pentamethyl-6-hydroxychroman under similar conditions produced the analogous product, 5-ethoxymethyl-2,2,7,8-tetramethyl-6-hydroxychroman together with 5-formyl-2,2,7,8-tetramethyl-6-hydroxychroman and 2-(3'-hydroxy-3'-methylbutyl)-3,5,6-trimethylbenzo-1,4-quinone.

Catalysis↗
PubMed1986

Classification of human tumours by high-resolution magnetic resonance spectroscopy.

Malignant tumours yield a high-resolution proton magnetic resonance (MR) spectrum. Fifty-one tumour biopsy specimens from patients with cancer of the ovary or colon were examined by magnetic resonance spectroscopy (MRS) to determine whether it was possible to identify tumour subtypes with metastatic potential. Relaxation parameters (T2) for visible lipid methylene protons were within the range of those measured for three animal metastasis models. Primary carcinomas with metastases gave T2 values greater than 350 ms, whereas carcinomas not associated with known metastases at the time of tumour excision gave a range of values from 150 to 1500 ms. All but two carcinomas gave a long T2 (greater than 350 ms) indicating metastatic potential. The MRS method designated five of six histologically borderline epithelial ovarian tumours as malignant with metastatic potential. MRS may be sensitive enough to detect malignant cells in a tumour which is of intermediate or borderline malignancy by light microscopy. Malignancy without a potential for metastasis is uncommon.

Colonic Neoplasms↗
PubMed1985

Stereospecific removal of methyl phosphotriesters from DNA by an Escherichia coli ada+ extract.

The ada+ gene product, a DNA methyltransferase present in extracts from an Escherichia coli strain constitutive for the adaptive response, removes only half of the methyl phosphotriesters from alkylated DNA. Since DNA phosphotriesters occur in two isomeric configurations (denoted Rp and Sp), we examined whether this reflects a stereospecific mode of repair by the methyltransferase. Analysis by reverse-phase HPLC, phosphorus NMR and circular dichroism established that only triesters in the Sp configuration are acted upon by the E. coli extract.

Alkylating Agents↗
PubMedDate not supplied

400 MHz NMR study on the C-terminal fragment 21-28 of vasoactive intestinal peptide.

A conformational study of the C-terminal fragment 21-28 of vasoactive intestinal peptide (VIP) was carried out by high resolution NMR spectroscopy. All spectral data were recorded with a Brüker 400 MHz spectrometer. The correct assignment of peaks was determined by specific homonuclear decoupling and by titration. The chemical shifts of amide protons were measured as a function of temperature in order to detect the presence of intramolecular hydrogen bonds. A tridimensional structure is proposed for the peptide.

Gastrointestinal Hormones↗
PubMedDate not supplied

Synthesis, conformational studies and biological activities of VIP and related fragments.

VIP and related fragments were prepared by the solid-phase method. The peptides were assembled on a benzhydrylamine resin and couplings of the Boc-amino acids were carried out by the symmetrical anhydride method. Cleavage was achieved by treatment with liquid HF and purification was accomplished by successive steps of cation exchange, partition and semi-preparative high pressure liquid chromatography. The biological activities were evaluated in vitro in the rabbit perfused heart and in vivo on the rat blood pressure. Structural studies were performed by high resolution (400 MHz) 1H-NMR spectroscopy and circular dichroism. The results show that among all the fragments tested, only VIP2-28 retains significant biological activity. The fragments 1-14 and 15-28, which are devoid of activity, were found to be inactive as antagonists. VIP and some of the fragments tend to adopt the helical structure, as demonstrated by spectroscopic techniques.

Amino Acid Sequence↗