Biomedical subjects

P D Hockings

Publications and source records attributed to P D Hockings.

10 recordsLinked to original sources

PubMed2003

Rapid reversal of hepatic steatosis, and reduction of muscle triglyceride, by rosiglitazone: MRI/S studies in Zucker fatty rats.

AIM: This study aimed to chart the time course and durability of the effects of rosiglitazone, a potent thiazolidinedione-based peroxisome proliferator-activated receptor gamma agonist, on hepatic steatosis and intramyocellular lipid in an animal model of obesity, the Zucker Fatty (ZF) rat. METHODS AND RESULTS: Rosiglitazone (3 mg/kg/day p.o.) significantly reduced both liver fat content (by 59%; p < 0.05) and size (11.5%; p < 0.05) in male ZF rats that received between 3 days and 1 week of treatment, and these reductions were maintained for at least 12 weeks. Liver fat content measured by magnetic resonance spectroscopy (MRS) correlated closely and positively with plasma insulin levels (reduced by 89% within a week, r = 0.8) and with postmortem histological fat fractional volume (r = 0.89). Similarly, liver volume measured by magnetic resonance imaging (MRI) correlated closely with postmortem wet weight (r = 0.99). MRS also showed, and numbers of lipid vacuoles counted in transmission electron micrographs confirmed, that rosiglitazone significantly reduced the elevated intramyocellular lipid seen in ZF rat skeletal muscle by at least 40% (p < 0.05). CONCLUSIONS: Localized MRS and MRI showed that rosiglitazone reversed the hepatic steatosis, hepatomegaly and intramyocellular lipid, characteristic of the ZF rat, an animal model of obesity.

Animals↗

PubMed2002

Extended acclimatization is required to eliminate stress effects of periodic blood-sampling procedures on vasoactive hormones and blood volume in beagle dogs.

Important in all experimental animal studies is the need to control stress stimuli associated with environmental change and experimental procedures. As the stress response involves alterations in levels of vasoactive hormones, ensuing changes in cardiovascular parameters may confound experimental outcomes. Accordingly, we evaluated the duration required for dogs (n = 4) to acclimatized to frequent blood sampling that involved different procedures. On each sampling occasion during a 6-week period, dogs were removed from their pen to a laboratory area and blood was collected either by venepuncture (days 2, 15, 34, 41) for plasma renin activity (PRA), epinephrine (EPI), norepinephrine, aldosterone, insulin, and atrial natriuretic peptide, or by cannulation (dogs restrained in slings; days 1, 8, 14, 22, 30, 33, 37, 40) for determination of haematocrit (HCT) alone (days 1 to 22) or HCT with plasma volume (PV; days 30 to 40). PRA was higher on days 2 and 15 compared with days 34 and 41 and had decreased by up to 48% by the end of the study (day 41 vs day 15; mean/SEM: 1.18/0.27 vs 2.88/0.79 ng ANG I/ml/h, respectively). EPI showed a time-related decrease from days 2 to 34, during which mean values had decreased by 51% (mean/SEM: 279/29 vs 134/20.9 pg/ml for days 2 and 34, respectively), but appeared stable from then on. None of the other hormones showed any significant variability throughout the course of the study. HCT was relatively variable between days 1 to 22 but stabilized from day 30, after which all mean values were approximately 6% lower than those between days 1 and 8. We conclude that an acclimatization period of at least 4 weeks is required to eliminate stress-related effects in dogs associated with periodic blood sampling.

Acclimatization↗

PubMed2001

Ischaemic preconditioning in the rat brain: a longitudinal magnetic resonance imaging (MRI) study.

Ischaemic preconditioning in rats was studied using MRI. Ischaemic preconditioning was induced, using an intraluminal filament method, by 30 min middle cerebral artery occlusion (MCAO), and imaged 24 h later. The secondary insult of 100 min MCAO was induced 3 days following preconditioning and imaged 24 and 72 h later. Twenty-four hours following ischaemic preconditioning most rats showed small sub-cortical hyperintense regions not seen in sham-preconditioned rats. Twenty-four hours and 72 h following the secondary insult preconditioned animals showed significantly smaller lesions (24 h = 112 +/- 31 mm(3), mean +/- standard error; 72 h = 80 +/- 35 mm(3)), which were confined to the striatum, than controls (24 h = 234 +/- 32 mm(3), p = 0.026; 72 h = 275 +/- 37 mm(3), p = 0.003). In addition during lesion maturation from 24 to 72 h post-secondary MCAO, preconditioned rats displayed an average reduction in lesion size as measured by MRI whereas sham-preconditioned rats displayed increases in lesion size; this is the first report of such differential lesion volume evolution in cerebral ischaemic preconditioning.

Animals↗

PubMed2000

Mice overexpressing human uncoupling protein-3 in skeletal muscle are hyperphagic and lean.

Uncoupling protein-3 (UCP-3) is a recently identified member of the mitochondrial transporter superfamily that is expressed predominantly in skeletal muscle. However, its close relative UCP-1 is expressed exclusively in brown adipose tissue, a tissue whose main function is fat combustion and thermogenesis. Studies on the expression of UCP-3 in animals and humans in different physiological situations support a role for UCP-3 in energy balance and lipid metabolism. However, direct evidence for these roles is lacking. Here we describe the creation of transgenic mice that overexpress human UCP-3 in skeletal muscle. These mice are hyperphagic but weigh less than their wild-type littermates. Magnetic resonance imaging shows a striking reduction in adipose tissue mass. The mice also exhibit lower fasting plasma glucose and insulin levels and an increased glucose clearance rate. This provides evidence that skeletal muscle UCP-3 has the potential to influence metabolic rate and glucose homeostasis in the whole animal.

Adipose Tissue↗

PubMed1997

Thermodynamic significance of the lactate gradient.

The theory that some bacteria can save energy by an energy-recycling process, in which protons are excreted with metabolic end-products with variable stoichiometry, has been examined by 1H-NMR. A method has been developed that utilises observed differences in the Hahn T2 relaxation of metabolites in the intracellular and extracellular compartments to distinguish and quantify metabolite signals originating from both compartments. It was found that the lactate electrochemical-potential gradient calculated from the fraction of lactate that is sufficiently mobile to contribute to the NMR signal was in exact balance with the proton electrochemical-potential gradient over a wide range of pH values. The conclusion was reached that previous reports of variable stoichiometry were due to 'bound' lactate at high intracellular pH that could neither contribute neither to the NMR signal nor to the lactate electrochemical-potential gradient.

Enterococcus faecalis↗

PubMed1996

The measurement of transmembrane electrical potential with lipophilic cations.

The binding of lipophilic cation probes of membrane potential to cells was re-examined. Even concentrations of probe molecules as low as 100 nM were found to reduce delta psi and thus many commonly used techniques for delta psi determination are inappropriate. Binding was found to be a linear function of probe concentration and independent of pH. The proportionality constant for binding has been equated to an "apparent binding volume' for [3H]TPP+ with units of microliter/mg dry weight of cells. This "apparent binding volume' is thermodynamically equivalent to the volume of cell membrane multiplied by the partition coefficient of [3H]TPP+ for cell membrane and was equivalent to 9.10 +/- 0.33 microliters/mg dry weight in Enterococcus faecalis. It was concluded that the most accurate method for delta psi determination was to use nanomolar concentrations of lipophilic cations and appropriate correction for energy dependent binding.

Cations↗

PubMed1995

Image directed proton spectroscopy of gerbil brain at 7 tesla.

Image directed localized 1H NMR spectra were obtained at 7 T (300 MHz) from cubic volumes of less than 40 microL in the gerbil brain. Signals from cerebral metabolites commonly detected in other rodent species were easily assigned, and high resolution spectroscopy (360 MHz) of aqueous brain extracts assisted the tentative identification of partially overlapping resonances from lower concentration compounds like alanine, lysine, gamma-aminobutyrate, valine, leucine and isoleucine. Weak coupling at 7 T was manifest in the resolution of signals from the gamma-CH2 groups of glutamine and glutamate. Down-field of water, signals assigned to purine nucleotides were conspicuous in the extract spectra, but localized spectra acquired routinely in vivo, using selective excitation and gradient crushing (SUBMERGE) for water suppression, exhibited little or no signal from purines. When localized in vivo spectra were acquired without water suppression, however, or using a low power binomial excitation sequence rather than SUBMERGE, a broad signal appeared at the resonant frequency of purine aromatic protons. NMR experiments on the nucleotide adenosine 5'-monophosphate (AMP) in 90% glycerol/10% D2O solution demonstrated that pre-irradiation of the water signal even for less than 100 ms attenuated the nucleotide signal appreciably. This implies that the soft pulses required for selective excitation of water in sequences such as SUBMERGE induce spin-diffusion which eliminates or diminishes the signal from nucleotides in vivo.

Acetates↗

PubMed1994

1H NMR determination of intracellular volume in cell suspensions.

A 1H NMR method has been developed for determining the intracellular and extracellular volumes in a cell suspension. The method is quick, simple, and inexpensive. A comparison of the ratios of the water and Tris buffer resonances in a cell suspension and in a buffer solution gives the intracellular volume. The most important precaution to take is to ensure that coil loading is identical in both solutions and that the NMR signal is not saturating. The method was validated with a 20% polyethylene glycol solution. A comparison with radiolabel methods for volume determination found that the radiolabel probe of extracellular volume did not penetrate the cell wall water of Enterococcus faecalis, resulting in an overestimation of the intracellular volume, and that tritiated water probably exchanged with macromolecules, causing an underestimation of intracellular volume.

Enterococcus faecalis↗

PubMed1992

Selective intracellular lactate invisibility in Enterococcus faecalis.

In this article we will demonstrate that differences in Hahn T2 relaxation of the 1H NMR signal from cytosolic and extracellular lactate can be exploited to monitor lactate concentration gradients in bacterial cells and provide information on lactate transport mechanisms. As a by-product of this study we have determined that there are at least three pools of lactate in bacterial cells with differing visibility in the NMR experiment. This has serious implications for the spectral editing techniques that are so vital for in vivo spectroscopy.

Biological Transport↗

PubMedDate not supplied

Correlation between high-field T2-weighted MR imaging and histology of ischemic lesions in gerbil brain.

Global forebrain ischemia in the Mongolian gerbil is a common animal model for use in stroke research. We produced lesions of graded severity in gerbil brains (after prescreening by MR imaging) by performing 6-minute bilateral carotid artery occlusions while monitoring pericranial temperature with a temporalis muscle thermocouple probe and maintaining the temperature at 32 degrees C, 36 degrees C, or 40 degrees C. Lesion severity was scored 4 days after occlusion from findings on spin-echo images acquired at 7 T and from histologic scores. Statistically significant correlation was observed between the MR imaging score and brain temperature and between the MR imaging score and the area of the CA region of the hippocampus measured by histology. In addition, because prescreening with MR imaging revealed abnormalities in the hippocampus of some of the animals, and these animals were rejected from the study, the statistical significance of the result could be strengthened.

Animals↗