PubMed Health⌕ Search

Biomedical subjects

J B Aguayo

Publications and source records attributed to J B Aguayo.

12 recordsLinked to original sources
PubMed1992

Comparison between B-scan ultrasound and MRI in the detection of diabetic vitreous hemorrhage.

The efficacy of proton magnetic resonance imaging (MRI) was evaluated and compared with that of B-scan ultrasound in the detection and differentiation of diabetic vitreous hemorrhage. Although conventional spin-echo MRI could not locate vitreous hemorrhages, gradient-recalled-echo (GRE) MRI readily did so. The aberrant signals appeared to originate from the interfacing between hemorrhages and the vitreous, and possibly also from the paramagnetic effect of the ferrous ion. The information provided by boundary/susceptibility detection, unique to the GRE sequence, is useful in delineating the extent of vitreous hemorrhage and hemolysis. However, for the diagnosis and follow up of diabetic vitreous hemorrhages, MRI appears no more informative than B-scan ultrasonography.

Aged↗
PubMed1991

Analysis of diabetic cataractogenesis using chemical-shift nuclear magnetic resonance microscopy.

We here report the analysis of single rabbit lenses under high-glucose stress using four-dimensional 13C nuclear magnetic resonance (NMR) spectroscopy (three spatial and one chemical-shift). We have produced spatial maps of lenticular metabolites (glucose, sorbitol, and lactate) with submillimeter in-plane resolution. The production of sorbitol and its inhibition are also presented. This is the first study to report regional tissue metabolism. We expect further improvements in spatial resolution and acquisition times that will enable localized kinetic studies in intact tissues.

Animals↗
PubMed1991

Analysis of concurrent glucose consumption by the hexose monophosphate shunt, glycolysis, and the polyol pathway in the crystalline lens.

A method based on 13C-NMR spectroscopy is described, in which the metabolism of [13C2]glucose was assessed in intact rat lenses. By analysing the ratio of 13C3/(13C2 + 13C3) lactate, a quantitative measurement of the hexose monophosphate shunt (HMPS) activity could be derived. Similarly, measurements of the time-dependent increase of lactate and sorbitol permitted the determination of the activity of the Embden-Meyerhof pathway and the polyol pathway, respectively. This method offers significant advantages over other biochemical and spectroscopic methods and allows for the first time a direct correlation between the activities of the polyol pathway and the HMPS.

Animals↗
PubMed1988

High resolution deuterium NMR studies of bacterial metabolism.

High resolution deuterium NMR spectra were obtained from suspensions of five bacterial strains: Escherichia coli, Clostridium perfringens, Klebsiella pneumoniae, Proteus mirabilis, and Staphylococcus aureus. Deuterium-labeled D-glucose at C-1, C-2, and C-6 was used to monitor dynamically anaerobic metabolism. The flux of glucose through the various bacterial metabolic pathways could be determined by following the disappearance of glucose and the appearance of the major end products in the 2H NMR spectrum. The presence of both labeled and unlabeled metabolites could be detected using 1H NMR spectroscopy since the proton resonances in the labeled species are shifted upfield due to an isotopic chemical shift effect. The 1H-1H scalar coupling observed in both the 2H and 1H NMR spectra was used to assign definitively the resonances of labeled species. An increase in the intensity of natural abundance deuterium signal of water can be used to monitor pathways in which a deuteron is lost from the labeled metabolite. The steps in which label loss can occur are outlined, and the influence these processes have on the ability of 2H NMR spectroscopy to monitor metabolism are assessed.

Bacteria↗
PubMed1988

Dynamic monitoring of corneal carbohydrate metabolism using high-resolution deuterium NMR spectroscopy.

Glucose metabolism in rabbit corneas was monitored with deuterium (D or 2H) NMR spectroscopy. The corneas were incubated in 5.5 mM deuterated glucose (glucose-6, 6-D2). A 2.5 micrograms change in lactate and a 4.1 micrograms change in glucose could be detected by the NMR method. The mean rates of glucose utilization and lactate production in intact rabbit corneas were 248- and 151 micrograms h-1, respectively. The lactate production/glucose utilization ratio of 0.60, i.e. 60% of total glucose is metabolized to lactate, confirms that glycolysis is the principal pathway for glucose catabolism. Further, based on enrichment of the HDO signal (which refers to the naturally abundant deuterium signal arising from deuterons in water), glucose oxidation through Krebs cycle and its associated pathways is estimated to be 90 micrograms h-1 or 36% of total consumption. The significant advantages of deuterium NMR spectroscopy over other NMR techniques (e.g. 13C spectroscopy) are: (1) shorter acquisition times because of the short relaxation times of deuterated metabolites; (2) the HDO signal can be used as the internal reference; and (3) significant reduction in cost and high availability of 2H-labeled compounds. Deuterium NMR spectroscopy is therefore a reliable and effective means with which the corneal glycolytic activity prior to transplantation can be readily assessed.

Animals↗
PubMed1987

The study of diabetic cataractogenesis in the intact rabbit lens by deuterium NMR spectroscopy.

The polyol pathway has been implicated in the process of diabetic cataractogenesis. We report the use of deuterium (2H) spectroscopy for dynamically monitoring the polyol and glycolytic pathways in the single intact rabbit lens. Using 2H labeled C-1 D-glucose, the formation of sorbitol from glucose and the metabolism of sorbitol to fructose was dynamically monitored at 5.5 mM and 35.5 mM glucose concentrations. The accumulation of sorbitol at 35.5 mM glucose concentration was prevented by the inhibition of aldose reductase using an inhibitor (Sorbinil). 2H spectra were obtained in short acquisition times because of the short T1's of deuterated metabolites. A further advantage of 2H spectroscopy is that the natural abundance resonance of water (HDO) can be used as an internal reference standard. These findings confirm previous studies and demonstrate for the first time by NMR spectroscopy activity in the polyol pathway at low glucose concentrations.

Aldehyde Reductase↗
PubMed1986

Glycolytic activity in the human cornea monitored with nuclear magnetic resonance spectroscopy.

This study confirms the feasibility of using nuclear magnetic resonance (NMR) spectroscopy to assess, noninvasively, glucose metabolism in isolated corneal tissue. Glycolytic activity of human corneas was analyzed by high-resolution NMR spectroscopy and spectrophotometric coupling assays. Glucose utilization and lactate formation were readily demonstrated in incubating intact and deepithelialized human corneas utilizing an NMR spectrometer with an array of spectra taken at ten-minute intervals over a period of nine hours. The lactate formation rate by biochemical coupling assays was determined to be approximately 0.50 mumol/hr in the intact cornea and 0.20 mumol/hr in the de-epithelialized cornea. Analysis by NMR spectroscopy of the rate of glucose utilization and lactate formation may be a useful means of determining human donor corneal viability.

Cornea↗
PubMed1986

Computed tomographic three-dimensional localization and compositional evaluation of intraocular and orbital foreign bodies.

A software program designed for the Siemens Somatom DR3 computed tomographic (CT) scanner provides improved diagnosis, localization, and etiologic description of intraocular and orbital foreign bodies. The program allows information to be analyzed in two different display formats. One format is that of multiplanar reconstruction of the eye and orbit, including an "oblique CT cube" image. This format produces an accurate "three-dimensional" display of both in vitro and in vivo intraocular and orbital foreign bodies. The second display format is that of a histogram. Using this analytic mode, nonmetallic intraocular and intraorbital foreign bodies can be differentiated from each other and from metallic foreign bodies, although individual metallic foreign bodies cannot be identified with respect to specific composition. The information provided by these two display formats substantially aids the clinician in the diagnosis and management of foreign bodies located within the orbit, particularly those located within the eye.

Animals↗
PubMed1985

Sorbitol/fructose metabolism in the lens.

The function of the sorbitol pathway, both as a secondary energy source and as an osmotic counterbalancing force, was examined. Rat lenses were incubated in media containing fructose as the primary exogenous energy source, and 31P nuclear magnetic resonance (NMR) spectra were accumulated. Fructose was found to be a sub-optimal but usable substrate for glycolysis. The utilization of fructose was further confirmed by a 14C fructose tracer study, using high-pressure liquid chromatography. Thus the intralenticular pool of sorbitol + fructose could serve as a secondary energy source during severe hypoglycemia in the diabetic lens. However, fructose is not a physiologically significant alternative to glucose. 13C NMR spectroscopy was employed to determine the kinetics of sorbitol/fructose accumulation in lenses incubated in 35.5 mM 13C1-glucose, and the sorbitol/fructose consumption after the preincubated lenses were transferred to media containing no glucose. Based on these kinetic studies, we concluded that the sorbitol pathway cannot generate sorbitol/fructose fast enough to offset increased osmotic pressure from high glucose levels in the aqueous humor of the diabetic eye. The contribution of osmotic equivalents from sorbitol + fructose, however, cannot be ignored.

Adenosine Triphosphate↗
PubMedDate not supplied

Nuclear magnetic resonance imaging of a single cell.

Nuclear magnetic resonance (NMR) imaging is now an established tool in clinical imaging and competes favourably with conventional X-ray computerized tomography (CT) scanning. The drive behind NMR imaging has primarily been in the area of whole-body imaging, which has been limited clinically to fields of up to 1.5 T (60 MHz). It is recognized that there may be substantial advantages in obtaining images with sub-millimetre spatial resolution. Also, there may be benefits to imaging at higher fields, since the signal increases as the square of the magnetic field. Using a modified 9.5 T 89-mm-bore high-resolution NMR spectrometer, we have now obtained the first NMR images of a single cell, demonstrating the advent of the NMR imaging microscope. The NMR microscope is expected to have considerable impact in the areas of biology, medicine and materials science, and may serve as a precursor to obtaining such resolutions on human subjects.

Animals↗