Biomedical subjects
Publications and source records attributed to S R Williams.
We report here how magnetic resonance imaging can be used to gain definitive information about tissue pathology by the combined use of spin-echo and gradient-echo sequences. We also show how artifacts arising from respiratory motion can be eliminated by using a simple respiratory gating technique.
Blood flow and phosphorus metabolites have been measured simultaneously in the murine RIF-1 tumour in vivo. Blood flow was measured using the H2 washout technique and 31P NMR spectroscopy was used to measure high energy phosphates, inorganic phosphate and intracellular pH within the tumour. Following NMR and flow measurements, hydralazine was administered and the measurements repeated. There was always a decrease in blood flow, and a fall in nucleoside triphosphate detected by NMR, after administration of hydralazine. At blood flows in excess of 15 mL 100 g-1 min-1, the nucleoside triphosphate/inorganic phosphate ratio was 1.0 or greater, whereas at flows in the range of 5-12 mL 100 g-1 min-1 the ratio fell to below 0.5, and at flows below 5 mL 100 g-1 min-1 there was no detectable resonance from nucleoside triphosphate.
Cerebral ischaemia was produced in 2 groups of gerbils by occlusion of the common carotid arteries for 30 minutes, resulting in cerebral oedema. In group 1 cerebral oedema was measured by specific gravity microgravimetry, and in group 2 brain metabolism and blood flow were measured by 31P and 1H NMR spectroscopy and hydrogen clearance respectively. In group 1 the brain water content did not return to control levels by 180 minutes of reperfusion. Energy metabolism, determined by 31P NMR spectroscopy returned to control by 12 minutes, intracellular pH (pHi) by 20 minutes, and lactate, determined by 1H NMR spectroscopy, by 50 minutes. There was a lag of about 10 minutes before lactate began to be cleared from the brain. We suggest that while pHi is low, Na+/H+ exchange will negate the Na+ extrusion driven by the Na+/K+ ATPase. When pHi approaches normal there will be a net extrusion of Na+, taking osmotic water with it, and presumably with passive washout of lactate. This may be the cause of the initial delay in lactate clearance.
In a blinded, prospective, dose-response pilot study of continuous estrogen-progestin replacement therapy, 77 thin, nonsmoking, white women, who were 12 to 60 months postmenopausal and had normal medical histories, were randomly assigned to receive one of five dose combinations of daily ethinyl estradiol and norethindrone acetate (20 micrograms and 1.0 mg, 10 micrograms and 1.0 mg, 10 micrograms and 0.5 mg, 5 micrograms and 1.0 mg, and 5 micrograms and 0.5 mg) or conjugated estrogens 0.625 mg on days 1 to 25 and medroxyprogesterone acetate 10 mg on days 16 to 25. An additional 10 women meeting the same criteria served as a comparison group by taking calcium only. During 12 months of therapy, continuous users had significantly less vaginal bleeding and spotting than did sequential users. As compared with baseline values, bone metabolism and computerized tomographic measurements of vertebral trabecular bone density at month 12 indicated reduced bone turnover and increased density in hormone users. Endometrial biopsy specimens were negative for hyperplasia and neoplasia. The continuous ethinyl estradiol-norethindrone acetate tablet, even at the lowest doses studied, provided the same salutary effects on bone, endometrium, and postmenopausal symptoms as sequential therapy while minimizing annoying vaginal bleeding and spotting.
We have characterized sequences expressed in Chinese hamster ovary (CHO) cells which are related to the intracisternal A-particle (IAP) genes of mice and Syrian hamsters. Several cDNA clones homologous to Syrian hamster IAP probes have been isolated and used to evaluate the abundance and expression of these retroviruslike sequences. DNA blot analysis with homologous Chinese hamster IAP probes revealed that IAP-related sequences are present in CHO cell DNA at moderately repetitive levels (approximately 300 copies per haploid genome). Sequence analysis has revealed the existence of at least two distinct families of IAP-related sequences in CHO cell DNA. Family I sequences exhibit identical 4.5-kilobase-pair internal deletions relative to complete IAP genomes of mice or Syrian hamsters, but family II sequences showed no major sequence discontinuities relative to the IAP genes of other species. Both families are expressed as abundant cytoplasmic RNA in CHO cells, but only family II sequences produce abundant transcripts of a size consistent with that of a full-length IAP RNA. Intact gag, pol, or env open reading frames were not present in sequences of either family, although incomplete open reading frames spanning putative p27 and protease regions of IAP genes were observed.
Studies were made of the mechanism whereby hepatic gluconeogenesis is increased in diabetic ketoacidosis (DKA) despite evidence in vitro of inhibition of gluconeogenesis by systemic acidosis. In perfused livers taken from normal rats, marked inhibition of lactate uptake and glucose output was achieved by simulation of metabolic acidosis in the perfusate. In perfused livers obtained from animals with DKA, lactate uptake and glucose output were greater than in normal perfused liver at all values of perfusate pH, and it was not possible to demonstrate significant inhibition of gluconeogenesis from lactate by perfusate acidosis. Varying severity of acidosis was induced in rats by (a) HCl infusion, (b) NH4Cl ingestion or (c) experimental DKA. Hepatic intracellular pH (pHi) was measured in vivo by 31P-n.m.r. spectroscopy. Whereas at the severer degrees of systemic acidosis marked falls in hepatic pHi were seen in the HCl- and NH4Cl-treated animals, little fall was seen in rats with DKA. The protection of hepatic pHi in rats with DKA was not due to differences in respiratory compensation compared with the other groups. It is suggested that this protection of hepatic pHi in DKA may be responsible for the failure of acidotic inhibition of gluconeogenesis from lactate. Possible reasons for pHi protection in DKA are considered. There is no difference in hepatic energy status as assessed in vivo by ATP/Pi ratios between control, DKA and NH4Cl-treated rats. DKA rats show a striking decrease in hepatic glycerophosphoethanolamine content.
Explore the source record for details and available documents.
31P NMR spectra of the rat liver were recorded in vivo at 2.35 and 8.5 T. There was a large peak in the phosphodiester region of spectra obtained at 2.35 T which was much reduced at 8.5 T. The peak at 2.35 T is unlikely to be primarily from free cytosolic phosphodiesters, which would not be expected to display such a marked field dependence.
1H NMR spectroscopy of human brain in vivo can be used to detect a number of cerebral metabolites including N-acetylaspartate, creatine + phosphocreatine and choline-containing compounds. We have used 1H NMR spectroscopy to analyse these signals in (i) biopsy material from both normal human brain and astrocytomas, and (ii) primary astrocyte cultures. On the basis of this analysis, we conclude that in vivo 1H NMR spectroscopy could play an important clinical role in the non-invasive assessment of neuronal degeneration and proliferation of non-neuronal cells.
1H NMR spectroscopy of brain extracts was used to investigate the metabolic changes that take place during development of the neonatal rat brain. Data were obtained over the range 1-21 days. The concentration of N-acetylaspartate rose by a factor of 9 during this period, the most rapid rise occurring after day 9. The total creatine concentration rose from days 1-21, with a large increase between days 1 and 5. Taurine concentration rose until day 5, then fell from days 5-21. The concentration of choline-containing compounds fell during the 21 day period. The results are discussed in relation to brain development and conventional biochemical data. A major conclusion in relation to spectroscopy of children is that interpretation of changes seen in disease will require adequate data from age-matched controls.
[31P]- and [1H]Nuclear magnetic resonance spectroscopy were used to study metabolism in cortical brain slices in the guinea-pig during acute exposure to pathophysiological concentrations of ammonia. Intracellular acidification, measured from the chemical shift of endogenous inorganic phosphate, was observed without any change in cellular energy status or concentrations of lactate, glutamate and glutamine. The initial acidification, which developed over a period of 9 min appeared to be heterogeneous, on the basis of a splitting of the inorganic phosphate resonance in a number of experiments, corresponding to pH changes of 0.07 and 0.27 pH units. Subsequently a homogeneous acidification, of 0.15 pH units, developed by 23 min following exposure to ammonia. Intracellular pH recovered within 6 min after discontinuation of the ammonia load. In the absence of external bicarbonate, intracellular pH was 0.12 units more acidic than in the bicarbonate buffer and ammonia caused a further acidification by 0.16 units. When glutamine synthase inhibitor, methionine sulphoximine, was added, there was a slow fall in intracellular pH. Under these conditions, subsequent addition of ammonia failed to cause acidification directly. Thus acute elevation of ammonia does not lead to a change in cerebral high-energy phosphate or lactate metabolism, but may be associated with a fall in cortical intracellular pH.
Investigation into the underlying disease causing an aural polyp is often hampered when the polyp itself obscures the tympanic membrane. This retrospective analysis of 65 patients undergoing aural polypectomy was carried out to identify any predictive factors for underlying cholesteatoma and to determine a correct management strategy for aural polyps. The duration of symptoms, size of polyp, size of conductive component of hearing loss and bacteriology of otorrhoea were unhelpful as predictors of the underlying disease. Radiological evidence of bony erosion of the mastoid is a useful sign of cholesteatoma when present. Aural polypectomy resulted in 58.3 per cent of ears becoming inactive. It is proposed that aural polypectomy and histological assessment should be employed as initial treatment with mastoid exploration reserved for those ears thus identified as high risk for cholesteatoma.
The COOH terminus of decay accelerating factor (DAF) contains a signal that directs attachment of a glycophospholipid (GPI) membrane anchor. To define this signal we deleted portions of the DAF COOH terminus and expressed the mutant cDNAs it CV1 origin-deficient SV-40 cells. Our results show that the COOH-terminal hydrophobic domain (17 residues) is absolutely required for GPI anchor attachment. However, when fused to the COOH terminus of a secreted protein this hydrophobic domain is insufficient to direct attachment of a GPI anchor. Additional specific information located within the adjacent 20 residues appears to be necessary. We speculate that by analogy with signal sequences for membrane translocation, GPI anchor attachment requires both a COOH-terminal hydrophobic domain (the GPI signal) as well as a suitable cleavage/attachment site located NH2 terminal to the signal.
This study investigates whether phosphate metabolite concentrations and intracellular pH alter in early acute rejection of rat pancreatic allografts. In vitro biochemical assays, in vitro 31P nuclear magnetic resonance spectroscopy, and in vivo 31P NMR spectroscopy of the grafts were compared. Duct-ligated, vascularized rat pancreatic isografts and allografts were transplanted onto the infrarenal aorta of the recipients with inferior vena cava venous drainage. In order to obtain reproducible acute rejection, allografting was performed across a major histocompatibility barrier. For the in vitro experiments freeze-clamped graft extracts were prepared and analyzed for adenosine triphosphate concentration by fluorimetry, then placed in an 8.5 Tesla vertical bore magnet. 31P NMR spectra were recorded using a Bruker AM 360 spectrometer operating at 145.7 MHz for 31P. Spectra were acquired from nontransplanted controls; 3-day, 5-day, and 1-month posttransplant isografts, and 3-day and 5-day posttransplant allografts. All grafts examined were functioning satisfactorily. The ATP content of the extracts was significantly lower in the 3- and 5-day allografts than the respective isografts. Invasive in vivo 31P NMR spectra were recorded using surface coils adjacent to the grafts from functioning 5-day posttransplant isografts and allografts (i.e., 3 days prior to an expected elevation in blood sugar from acute rejection in the allografts). The ATP/inorganic phosphate ratios and pH from the in vivo spectra were significantly lower in the allografts than in the isografts. It is concluded that changes in intracellular metabolism occur early in the process of acute rejection and that 31P NMR spectroscopy may provide a means of diagnosing this before current methods.
Acute liver failure was induced in rats by a single intragastric dose of carbon tetrachloride. This causes hepatic centrilobular necrosis, as indicated by histological examinations, and produces a large increase in the activity of serum alanine aminotransferase. The plasma NH4+ level (mean +/- SEM) was 123 +/- 10 microM in the control group and 564 +/- 41 microM in animals with acute liver failure (each n = 5). 31P nuclear magnetic resonance (NMR) was used to monitor brain cortical high-energy phosphate compounds, Pi, and intracellular pH. 1H NMR spectroscopy was utilised to detect additional metabolites, including glutamate, glutamine, and lactate. The results show that the forebrain is capable of maintaining normal phosphorus energy metabolite ratios and intracellular pH despite the metabolic challenge by an elevated blood NH4+ level. There was a significant increase in the brain glutamine level and a concomitant decrease in the glutamate level during hyperammonaemia. The brain lactate level increased twofold in rats with acute liver failure. The results indicate that 1H NMR can be used to detect cerebral metabolic changes in this model of hyperammonaemia, and our observations are discussed in relation to compartmentation of NH4+ metabolism.
In this review, we assess the role of nuclear magnetic resonance (NMR) spectroscopy as a noninvasive method of studying metabolism in cerebral ischaemia. Phosphorus-31 NMR provides a monitor of intracellular pH and energy metabolites, including ATP, phosphocreatine, and inorganic phosphate, while other nuclei, including 1H, 13C, 19F, and 23Na can give additional information about several aspects of brain metabolism and physiology. For example, 1H NMR not only provides excellent images, but may also be used to monitor a range of metabolites, including lactate and several amino acids. Comparisons are made with the large body of information that is available from more traditional methods of studying metabolism. Emphasis is placed on the correlation of NMR data with parallel measurements of regional blood flow, tissue oxygenation, oedema, electrical activity, and tissue damage. Technical aspects of NMR are discussed where appropriate; for example, in relation to the range of metabolites that are accessible to study, the spatial resolution that is available for studies of focal lesions, problems arising from tissue heterogeneity, and quantification of metabolite levels. Applications in animal models and in humans are discussed; these primarily involve the 31P nucleus, but for the future it appears that 1H NMR studies offer particular promise.
Photodynamic therapy utilizes a tumour-localizing photosensitive substance which, when activated by light of an appropriate wavelength, releases cytotoxic substances causing destruction of the malignant tumour with preservation of surrounding normal tissues. In this technique the only drug/light combination which has been regularly used to date is that of haematoporphyrin derivative and red light at a wavelength of 630 nm usually produced by a dye or gold vapour laser. A pilot/feasibility study was set up in Southampton in 1983, with ethical permission, to treat tumours of the skin and head and neck which had failed all other treatment modalities or for which there was no practical alternative therapy. Thirty-eight patients were treated in this study and all tumours showed a response; significant palliation was achieved in a number of patients. Basal cell carcinomas and the multiple lesions of Bowen's disease were found to be particularly suitable for this form of therapy and prolonged local control was achieved in a number of patients.
1H NMR was used to detect lactate accumulation in the intact gerbil brain postmortem. The lactate concentration was estimated from the spectra by comparison to signals from N-acetylaspartate, creatine + phosphocreatine, and water. The effects of T2, phase modulation, and solvent suppression were taken into account. The estimated concentrations were compared to determinations performed on the same brains after extraction. The lactate concentration estimated from the intact brain spectra was between 70 and 90% of the values determined in vitro, on the extracts, depending on the concentration standard used. If N-acetylaspartate was used as the standard then the proportion of detected lactate (92%) was not significantly different from 100%.