Azu Owunwanne

Is 99Tcm hexamethyl-propyleneamine oxime uptake in the tissues related to glutathione cellular content?

The relationship between the concentration of tissue glutathione (GSH) content and uptake of 99Tcm HMPAO in Sprague Dawley rats was investigated. The GSH content of rat tissue was depleted with diethyl-maleate (DEM) and the ratio of GSH in control to GSH depleted rat was approximately twice that in the brain, liver, kidney, spleen and lung. The GSH content in all the organs studied except the liver had no statistically significant relationship with the uptake of 99Tcm HMPAO. The apparent increase of radioactivity in the liver was due to longer retention of 99Tcm HMPAO. This longer retention was due to stasis of bile flow as confirmed by subsequent experiments in which cholecystokinin (CCK).was administered to GSH depleted rats and compared to the uptake of GSH depleted rats without injection of CCK.

Cerebral circulation during endotoxic shock with special emphasis on the regional cerebral blood flow in vivo.

Left hemispheric blood flow was measured in eight adult Australian sheep prior to and, 1, 4, 30 and 60 min after the injection of endotoxin, E. Coli, 3 mg kg-1 bodyweight, using a radioisotope method. The mean left hemispheric blood flow prior to septic shock was 200 ml min-1 from which it rapidly reduced to 86 ml min-1 (1 min), and after a short recovery gradually decreased to 39 ml min-1 (60 min). Regional cerebral blood flow showed the highest value in the occipital region prior to septic shock, whereas 60 min after the endotoxin administration it reduced to the same low flow level, as in the other areas of the brain.

Pathophysiology and Mechanisms of Radiopharmaceutical Localization

2.5 Mechanism(s) of Radiopharmaceutical Localization 34 2.5.1 Isotope Dilution 35 2.5.2 Capillary Blockade 35 2.5.3 Physicochemical Adsorption 35 2.5.4 Cellular Migration and Sequestration 35 2.5.5 Membrane Transport 36 2.5.5.1 Simple Diffusion 36 2.5.5.2 Facilitated Diffusion 38 2.5.5.3 Active Transport 38 2.5.5.4 Phagocytosis 39 2.5.5.5 Receptor-Mediated Endocytosis 40 2.5.6 Metabolic Substrates and Precursors 40 2.5.6.1 Precursors: Radiolabeled Amino Acids 40 2.5.7 Tissue Hypoxia 41 2.5.8 Cell Proliferation 41 2.5.9 Specific Receptor Binding 42 2.5.9.1 Radiolabeled Peptides 42 2.5.9.2 Steroid Hormone Receptors 43 2.5.9.3 Adrenergic Presynaptic Receptors and Storage 44 2.5.9.4 LDL Receptors 44 2.5.9.5 Radiolabeled Antibodies 44 2.5.10 Imaging Gene Expression 46

Direct platelet effect of low molecular weight dextran in small calibre PTFE grafts.

The thrombogenicity of synthetic vascular grafts is a major factor in occlusion of grafts when they are used to bypass small calibre arteries. In this paper, the effect of low molecular weight dextran (LMWD, Dextran-40) on graft surface-platelet interaction was studied using Indium-III-oxine labelled platelets. It was found that LMWD significantly reduced platelet deposition onto graft surfaces (P less than 0.001). Dextran had a direct antiplatelet effect independent of plasma volume expansion as dextran-soaked grafts significantly reduced platelet deposition when compared to systemic dextran administration (P less than 0.001). We therefore conclude that LMWD has a direct antiplatelet effect which is beneficial in reducing platelet deposition on synthetic PTFE grafts which may improve the early patency of such grafts.

A miniaturized rapid paper chromatographic procedure for quality control of technetium-99m sestamibi

A miniaturized rapid paper chromatographic technique (MRPC) for quality control of a technetium-99m sestamibi preparation was developed and compared with the manufacturers and Hung et al. techniques. The MRPC system involves the use of 6.0×0.5 cm Whatman 3MM paper strip developed in ethyl acetate. The procedure was completed within 3 min while that of the manufacturer and Hung techniques took 30–35 and 4 min respectively. The Rf range of99mTc-sestamibi using MRPC was 0.55–0.75 while that of the other two techniques was 0.9–1.0. The results indicate that MRPC can be used to separate99mTc-sestamibi from any99mTc contaminant that migrates with the solvent front. The MRPC is a fast and effective chromatographic technique for routine quality control testing of99mTc-sestamibi preparation.

Forskolin Impregnation of Small Calibre PTFE Grafts Lowers Early Platelet Graft Sequestration and Improves Patency in a Sheep Model

Synthetic vascular grafts have a thrombogenic surface which plays a role in graft failure. Systemic pharmacologic interventions have been used to lower platelet sequestration onto the graft surface but are associated with side effects. In this communication we describe the results of a new therapeutic principle of applying forskolin, a powerful cyclic adenosine monophosphate stimulator (cAMP) to the inner surface of PTFE vascular grafts. The grafts were evaluated with Indium-III-oxine labelled platelets and by graft patency on 3 consecutive days after implantation at 1 month and 3 months. Forskolin significantly lowered early platelet sequestration onto the treated graft surface when compared with controls. Graft potency at 1 and 3 months was also significantly higher in the forskolin treated grafts.

Leucocyte sequestration in endotoxemia and the effect of low-molecular-weight dextran

Leucocyte sequestration in various organs during endotoxin-induced shock in sheep was studied using leucocytes labelled with indium 111 oxine. A moderate dose ofEscherichia coli endotoxin (10 μg/kg body weight) was slowly infused intravenously in 16 sheep, 9 of which subsequently received a continuous i.v. infusion of low-molecular-weight dextran (LMWD) given at an infusion rate of 15 ml/h over 4 h, starting 30 min after administration of the endotoxin. By that time, signs of acute lung injury had developed, thus mimicking a clinical situation. The remaining animals were untreated and served as controls. A marked increase in lung, liver and kidney leucocyte sequestration, together with a sharp, corresponding drop in splenic activity and leucocyte count in peripheral blood, occurred shortly after the endotoxin infusion in both groups. However, after 90 min there was a significantly lower leucocyte activity in the lungs, liver and kidneys of LMWD-treated animals as compared with controls. Less marked hemodynamic and respiratory alterations were also observed in animals treated with LMWD. The present study confirms previous reports that significant leucocyte sequestration in the lungs occurs early during endotoxemia. Furthermore, we found that leucocyte sequestration also occurs in the liver and kidneys, which could explain the development of multi-organ failure, frequently described in clinical sepsis. Even after injury to organs, LMWD infusion seems to be beneficial by significantly lowering leucocyte sequestration and could therefore be justified as an addition to the arsenal of interventions used in the treatment of endotoxemia.

Eosinophils as a Direct Target of the Anti-Inflammatory Effect of Salmeterol: Demonstration with Indium-111-Labeled Eosinophils

Objective: The β2-adrenoceptor agonist salmeterol inhibits the accumulation of eosinophils at the site of allergic inflammation, but the cellular target is uncertain. This study was undertaken to determine whether eosinophils themselves are the target of this inhibitory action. Methods: Purified guinea pig peritoneal eosinophils were labeled with indium-111 oxine, pre-incubated with salmeterol or drug vehicle before being injected intravenously into guinea pigs, which have previously been immunized with ovalbumin (OA). Four hours after intradermal injection of OA or platelet-activating factor (PAF), the accumulation of labeled eosinophils at the injection sites was determined by measuring the radioactivity in punched-out skin sites. In vitro adhesion to plastic plate was also studied by measuring the eosinophil peroxidase content of adhering cells. Results: About 6% of the injected 111In-eosinophils were circulating 10 min after injection and remained relatively steady for over 4 h. In animals given vehicle-treated 111In-eosinophils an up to 3.6-fold increase in the accumulation of the labeled cells at the skin sites of OA or PAF injection was seen. Pretreatment of 111In-eosinophils with salmeterol (1 µM) – a concentration giving about 65% inhibition of in vitro adherence – had no effect on the basal (PBS-induced) skin accumulation of the injected cells. However, it inhibited the net accumulation induced by OA (0.01–1 µg/site) and PAF (0.01–1 nmol/site) by 58.8–100%. At 1 µM, salmeterol itself had no significant effect on the viability and circulation of 111In-eosinophils. Conclusion: These results provide evidence for a direct inhibitory effect of salmeterol on eosinophils and suggest that this may account for a significant part of its clinical anti-inflammatory properties.

Multiorgan Leukocyte Sequestration during Endotoxic Shock in Sheep

Following injection with indium-Ill-oxine-labeled leukocytes and Escherichia coli lipopolysaccharide, leukocyte sequestration was observed in the lungs, liver and kidneys in 6 sheep

Evaluation of 99Tcm mercaptoacetyltriglycine for the detection and localization of gastrointestinal bleeding in an experimental animal model.

Technetium-99m mercaptoacetyltriglycine (99Tcm-MAG3) was evaluated for the detection and localization of the site of gastrointestinal bleeding in a sheep model. Radioactivity was detected in both the stomach and lower abdomen. However, 99Tcm-MAG3 is partially excreted by the liver and in the bile. The radioactivity in the bile moved to the small bowel. This movement of radioactivity in the lower abdomen can lead to a misinterpretation of the site of bleeding. Hence, 99Tcm-MAG3 may not be an effective radiopharmaceutical for the localization of the site of bleeding in the gastrointestinal tract, particularly the lower abdomen.