Transfer Of Tracer Research Articles

The Deoxyglucose Method in the Ferret Brain. II. Glucose Utilization Images and Normal Values

To measure cerebral glucose utilization with the autoradiographic deoxyglucose method, the tracer transfer rate constants and lumped constants must be known. 2-Deoxyglucose (2-DG) and fluorodeoxyglucose (FDG) constants were determined in 18 gray and white matter brain structures of the anesthetized ferret. The ferret is a domestic carnivore particularly suitable for deoxyglucose studies because of its small brain size and low body weight. The average gray matter rate constants for tracer transfer across the blood-brain barrier are similar for 2-DG and FDG in the ferret brain (K*1 = 0.21 ml/g/min and k*2 = 0.39 min-1). The rate constant for the rate-limiting step of tracer phosphorylation, k*3, is 1.6 times higher for FDG than for 2-DG (0.21 vs. 0.13 min-1). Loss of metabolized tracer is about 1-1.5%/min throughout the ferret brain for both tracers as estimated for a 180 min experimental period. Taking into account this loss, the lumped constant is 0.92 for FDG and 0.68 for 2-DG. Glucose utilization values in the brain of the anesthesized ferret range from 33 mumol/100 g/min in the corpus callosum to 104 mumol/100 g/min in the caudate nucleus. Representative glucose utilization images of coronal sections of the ferret brain are shown. Brain structures are identified on the same slices counterstained with thionin.

Influx of a choline analog to dog brain measured by positron emission tomography.

The influx of the 11C-labeled choline analog pyrrolidinocholine into tissue was measured in the brain of three dogs by positron emission tomography (PET). During the first 90 s after the intravenous bolus injection of the tracer, transfer of tracer from plasma to tissue was unidirectional. The influx constant for pyrrolidinocholine into intracranial tissue, Kin, was 0.017 ml/g/min (0.008 SD), and the initial volume of distribution, V0, was 0.08 ml/g (0.03 SD). The influx constant was at least five times larger than the value expected if simple diffusion were to account for tissue uptake. The method presented in this paper can be used to investigate the availability of plasma choline and its analogs to the living human brain and other tissue in degenerative diseases affecting the cholinergic system, and to provide in vivo information on a choline transport system.

Differential modulation of rat follicle cell gap junction populations at ovulation

The hypothesis proposed in the late 1970s that meiotic resumption in mammalian oocytes might result from the disruption of gap junction communication between follicle cells and the oocyte has not been supported by metabolic cooperation experiments which demonstrate that exogenous tracer transfer from the cumulus oophorus to the oocyte does not decrease until several hours after germinal vesicle breakdown (GVBD). Since these studies utilized isolated cumulus-oocyte complexes for their measurements, however, they excluded from consideration the possible effect of separation of the cumulus oophorus from the membrana granulosa which was required for this assay. We considered the possibility that the disruption of cumulus junctions within the intact follicle could mimic this experimental manipulation and previously reported that cumulus gap junctions were dramatically down-regulated during the period of GVBD in vivo. In the present study, we have utilized quantitative morphometric techniques to analyze the responses of other gap junction populations in intact preovulatory rat follicles to an ovulatory stimulus and demonstrate now that membrana granulosa, cumulus, and cumulus-oocyte gap junctions are down-regulated at different times and rates during the preovulatory period. Although membrana gap junctions are down-regulated during the period of meiotic resumption, their loss is not as rapid or as complete as in the cumulus oophorus. Cumulus-oocyte gap junctions are down-regulated after meiosis resumes but during the same period other investigators have demonstrated a reduction in metabolite transfer between the cumulus oophorus and the oocyte. Our results are interpreted to suggest that the cumulus oophorus may regulate the conduction of meiosis inhibitory signals between the membrana granulosa and the oocyte.

Estimation of parameters affecting the uptake of 99mTc-methylenediphosphonate in rat femur with model simulation.

The uptake of 99mTc-methylenediphosphonate (MDP) in different parts of rat femur was simulated using a local three-space model for tracer transfer. The model consisted of bone blood, bone ECF-space and space for tracer deposition. The measured 99mTc-MDP concentration in the systemic blood and the local bone blood flow measured by 131I-macroaggregated albumin microspheres were used as input parameters. The measured blood flow values were 6.3, 3.1 and 15.3 ml/100 g/min for proximal, middle and distal femur, respectively. The model parameters that gave the best fit to measured 99mTc-MDP uptake curves in computer simulation showed that bone blood flow, volume of ECF-space, permeability surface area product and accretion constant from ECF-space to space for tracer deposition were highest in distal and lowest in middle femur. The values corresponded to peak extraction fractions of 0.38, 0.62, and 0.31 for proximal, middle and distal femur, respectively. We conclude that the simulation gives acceptable model parameters, and indicates applicability of a similar model into clinical quantitative bone scintigraphy.

An investigation of 11-methane, 13N-nitrous oxide and 13C-acetylene as regional cerebral blood flow agents

Radioisotopes of xenon or krypton are generally used as the inert diffusible indicators in regional cerebral blood flow (rCBF) studies. These gases have disadvantages when introduced into the body by inhalation because of their low solubility in body tissues. The use of 11C-methane, 13N-nitrous oxide and 11C-acetylene as inhalation rCBF agents has been investigated. These gases span a wide range of solubilities: methane is four times less soluble than xenon in body tissues while nitrous oxide and acetylene are respectively 3 and 6 times more soluble. Cerebral blood flow measurements were performed on normal volunteers using the three labelled gases as well as 133Xe. All tracers were administered by inhalation and the cerebral clearance of the gases was monitored by coincidence detection. Uptake in the body was found to be dependent on solubility. The computed blood flow values found using the various indicators were in excellent agreement and were within the normal cerebral blood flow range. The high solubilities of acetylene and nitrous oxide result in a more efficient transfer of tracer from lung to brain that the conventionally used agents. The positron emission is also advantageous for tomographic rCBF measurements.

Transient rate tracer studies in heterogeneous catalysis: Oxidation of carbon monoxide

Establishment of the mechanism of a catalytic reaction is important from the viewpoints of both catalyst development and construction of suitable rate equations for design purposes. The use of transient tracing employing isotopes is a useful tool for this purpose. In this paper, a new method is described in which the transfer of isotopic species is superposed on a heterogeneous catalytic reaction conducted under steady-state conditions. An efficient method of modeling the system of first-order differential equations describing tracer transfer is presented. The method is applied to the oxidation of carbon monoxide over hopcalite catalyst. A relatively simple model with one type of site for adsorbed carbon oxide species correlates the data well for both 13CO 2 and 13CO marking. The final step, CO 2 adsorption and desorption, is fast and reversible.

The electro-osmotic enhancement of the neutral tracer transfer through a capillary membrane

The convective transfer of uncharged solute through a capillary membrane under conditions of electro-osmosis with zero mean flow is considered. The velocity distribution across the capillary cross section induces the convective mass exchange between two compartments separated by the membrane. If some tracer concentration difference between both compartments is maintained, a field-dependent tracer flux through the membrane should be observed. This effect is akin to the well-known phenomenon of Taylor diffusion in laminar flow through capillaries. The tracer exchange will be further enhanced in the case of a membrane with randomly sized capillaries. Evaluation of the flow distribution in the parallel-pore membrane under conditions of zero mean flow enables prediction of the rate of the tracer transfer through the membrane, which is strongly dependent on the pore size distribution and may far exceed both molecular diffusion transfer and convective transfer through a membrane with identical capillaries. The rate of the field-induced tracer transfer is described by the effective diffusion coefficient, which is evaluated as a function of the electric field, tracer diffusivity, and pore size distribution.

The blood-brain barrier to horseradish peroxidase under normal and experimental conditions

This review paper deals with the transport of the protein tracer horseradish peroxidase across cerebral vessels under normal and various experimental conditions. Electronmicroscopical investigations have revealed that, under normal conditions, a minor vesicular transfer of intravenously injected peroxidase occurs across the endothelium in segments of arterioles, capillaries and venules, especially in arterioles with a diameter about 15-30 mu. This normally occurring vesicular transport is susceptible to various experimental conditions. Thus the transfer of tracer increases when a hypertonic solution is injected into the internal carotid artery presumably due to vesicular transport. Extensive acute hypertension of short duration also increases the vesicular transfer of peroxidase from blood to brain. Identical observations are obtained when the hypertension is evoked by intravenous injection of phentolamine and by electrically induced seizures. During the postischemic period, one hour after release of the occlusion of an internal carotid artery in the Mongolian gerbil the vesicular transport of peroxidase is increased across the endothelium of cerebral vessels. The explanation may be release of serotonin from blood platelets during the occlusion. The serotonin could then increase the blood pressure locally in the brain resulting in an enhanced permeability. Serotonin, after perfusion through the cerebral ventricular system, is also able to increase the normally occurring vesicular transfer. The most likely mechanism behind this phenomenon seems at the moment to be local hypertension evoked by serotonin-induced vasoconstriction of arterioles. Finally, the enhanced vesicular transport across cerebral endothelium caused by porto-caval anastomosis is mentioned and the possible role of disturbances in the metabolism of amines as responsible for the extravasation is discussed.

New Isotope Methods for Estimating Milk Intake and Yield

Two isotope tracer methods, based on the transfer of isotopic tracer via milk from a female to offspring, were developed for estimating milk intake of nursing offspring. One method depended upon the transfer of tritiated water from female to offspring in milk and simultaneous determination of water turnover of the offspring by deuterium oxide. The second method was based on the transfer of radiocesium from female to offspring in milk and required the use of whole body counting techniques for evaluating the radiocesium body burden of the offspring. Experiments evaluating the two methods were with hand-reared Holstein calves given fixed milk intake. The methods gave valid estimates of milk intake; estimates were within±2.5% of the actual intakes. The application and limitations of these methods for estimating milk intake and yield of other species are discussed.

Intracellular Kinetics of Tracer Chloride and Bromide inNitella translucens

The kinetics of transfer of 36C1 and 82Br to the vacuole of Nitella translucens have been com pared with the kinetics of transfer of the flowing cytoplasm in half-cell labelling experiments. About 40 per cent of the activity entering the cell reaches the flowing layers, much more than could be accounted for as the fast cytoplasmic phase seen in vacuolar kinetics. Also the specific activity in the flowing cytoplasm is proportional to time over the first 20 min of uptake, and is essentially constant during a 10-min wash period. Hence the major fraction of tracer in the flowing cytoplasm is in the slow phase of the cytoplasm. In spite of this there is ready movement of tracer from the flowing cytoplasm to the stationary cytoplasmic layer in the inactive end. It is concluded that the bulk (watery) phase of the cytoplasm is to be identified as the slow phase, and that the fast phase (if it exists as a real cytoplasmic compartment) can be only a very small membrane-bound phase within the bulk cytoplasm. It is shown that in the presence of 10 ml Mn2+, which makes the cells inexcitable, t here is little or no fast component of vacuolar transfer. The alternative explanation of the fast component, as an artefact arising from transfer of tracer associated with action potentials on cutting open the cell, may provide a more satis factory explanation of the kinetics. The kinetic characteristics of the slow phase and the lack of discrimination between chloride and bromide in the face of the link between vacuolar transfer and influx are still held to suggest ion transfer to the vacuole by the creation and discharge of salt-filled vesicles, rather than by processes of single ion transfer at pre-formed tonoplast.

Microinjection of 14C-sucrose and other tracers into isolated phloem strands of Heracleum

Microinjection of solutions of 14C-sucrose, 14C-aspartic acid, K332PO4, 42KCl, and 3HHO have all been made into living sieve elements of displaced, isolated, phloem strands of Heracleum. The profile of tracer movement is reported in experiments between 1 min 40 s and 8 min in duration in strands prepared both with and without callose-reducing buffer under conditions where lateral transfer of tracer is restricted. Two types of translocation patterns are discernable, a mass flow near the origin and a type of pulse flow superimposed on it and extending along the strands in both directions simultaneously. Some 42K and 32P has been detected with the 14C in the pulses, but 14C-sucrose also appears to move independently of the other tracers.

The perineurium as a diffusion barrier to protein tracers. Differences between mature and immature animals.

A study was made on the permeability of the sciatic nerve sheaths to various protein tracers in mature and immature animals. Albumin labelled with a fluorescent marker and injected around the sciatic nerve ofadult mice and rats did not penetrate the perineurium to reach the endoneurium. Insuckling mice and rats, the same tracer penetrated the perineurium and spread in the endoneurium of the sciatic nerve. A similar difference in permeability was found when horseradish peroxidase was used as a protein tracer. Newborn guinea pigs, on the other hand, showed a fully developed barrier function of the nerve sheaths to proteins. The difference in permeability between mature and immature animals was also present when tested 2 hours post mortem, demonstrating that the transfer of tracer into the endoneurium of immature animals is not dependent on an oxygen-consuming active process. It has previously been shown that in adult mice a) the perineurium is the structure to which the barrier function of the nerve sheaths is linked and b) the presence of tight junctions between the perineurial cells prevent intercellular diffusion of protein tracers. Ultrastructural observations showed that gaps are present between the cells forming the perineurial lamellae in the sciatic nerve of newborn mice. Horseradish peroxidase passed through these gaps into the endoneurium when injected around the nerve. The difference in permeability of the nerve sheaths between mature and immature mice is therefore presumably due to differences in the apposition of the perineural cells providing open pathways in the young but not in the adult mice.

Nutrient renal blood flow and its distribution in the unanesthetized dog

The initial arterial distribution of Rb 86 following a bolus intravenous injection of the tracer is proportional to the distribution of the cardiac output. For practical purposes, cardiac indicator washout after initial mixing follows a single exponential function up to the time of recirculation and, therefore, delivery of indicator to any organ approximates this same function. Subsequent to initial indicator delivery to the kidney, the net rate of Rb 86 redistribution is small. Renal blood flow directly measured from venous drainage in the dog was compared to that calculated by multiplying the cardiac output (determined by indicator dilution) by the renal indicator content at 30 seconds post-injection as a fraction of the injected indicator. A linear correlation of +0.93 was obtained. The renal blood flow calculated from these concepts was defined as nutrient blood flow. This is necessary, since it cannot presently be determined if indicator exchange between blood and tissue during capillary transit reached complete equilibrium or if there are anatomic anastomotic communications which limit the correlation between calculated and measured blood flow. Renal blood flows calculated in animals awake at the time of indicator delivery are substantially in agreement with the results obtained by other methods. There is an intrarenal blood flow distribution gradient from cortex to medulla of 7:1. Blood flow calculated from the intrarenal indicator distribution suggests that renal blood flow decreased proportionally from cortex to medulla in the resting dog. These results are substantially in agreement with reported measurements which do not depend on extravascular tracer transfer.

An Investigation of Bidirectional Translocation in the Phloem

Patterns of (14) CO(2) , assimilate movement in Vicia jaba plants having 7 nodes were studied. Bidirectional translocation occurred throughout most of the stem length when tracer was applied to leaves of various ages. To determine whether this bidirectional translocation occurs within single sieve tubes, a O.1 % solution of the fluorescent dye K-fluorescein was applied to a lightly scraped area on the stem in the middle of a young internode. After one hour the dye was present short distances above and below the treated area. Free-hand sections of the internode showed the dye to be localized in the traces of the larger leaves below tbe treated area and in the traces of the younger leaves above the treated area. The dye was never present in the same bundle both above and below the treated area, indicating that each bundle and sieve tube translocated the dye in only one direction. These results were confirmed using Phaseolus vulgaris, Vinca rosea, and Pelargonium hortum. A similar study in which petioles of young Ecballium elaterium leaves were treated showed that usually the phloem of one bundle translocated the dye in only one direction but in some cases the external phloem of the bicollateral bundles carried the dye toward the stem while the internal phloem carried the dye toward the blade. When longer time intervals were used in all these experiments, the dye sometimes appeared in the same phloem areas both above and below the treated area. This is explained by a lateral transfer of tracer within the phloem, either through secondary phloem or through bundle anastomoses at the nodes.

The effects of sickling on ion transport. II. The effect of sickling on sodium and cesium transport.

When the red cells from patients with sickle cell anemia (S-S) were kept in the disk shape by incubation in O(2), they maintained cell sodium in the steady state for at least 10 hours. The sodium flux in such cells at 37 degrees C. was 6.0 +/- 1.5 m.eq./ (liters RBC) x (hours). When S-S cells were sickled by incubation in N(2), sodium outflux increased two- to threefold, while influx increased four- to fivefold and the cells gained net sodium. A small but undetermined fraction of the sodium in disk and sickle shaped S-S cells exchanges at one or more rates which are substantially slower than those calculated here from the initial rate of transfer of tracer from cells to the medium. The penetration of tracer Cs into normal and both disk and sickled S-S cells was markedly inhibited by increasing the K concentration in the medium, indicating that Cs and K compete for an entrance pathway in all three cell types. The ratio of the inward rate constant for tracer Cs to that for K(42) in normal and disk-shaped S-S cells increased only slightly when the K concentration in the medium was increased, indicating that almost all the Cs entered such cells in competition with K. Sickling accelerated the entrance of tracer cesium into S-S cells. Furthermore, the rate constant ratio increased with increasing external K concentration in sickled cells, suggesting the simultaneous presence of a non-competitive route for cesium influx in this cell type. The results are interpreted to support the view that sickling (a) accelerates inward transport of K and Cs and outward transport of Na by a non-diffusion, assumed carrier, process and (b) opens pathways for the diffusion of all three ions.