No abstract

Summary: We measured, in vivo, the local concentration of nitric oxide (NO) in cerebral tissue, during and after transient middle cerebral artery occlusion in the rat (n = 8). Baseline concentration of NO was <10-8 M; upon initiation of ischemia, NO concentration increased to -10-6 M and then declined. Reperfusion likewise stim ulated an increase in NO concentration to above baseline Nitric oxide (NO) plays a multifaceted and im portant role in the brain. It is a neurotransmitter (Bredt et aI., 1991) and a free radical (Beckman, 1990(Beckman, , 1991, and it has been implicated in the regu lation of cerebral blood flow (Faraci, 1991;Faraci and Heistad, 1992; Kozniewski et aI. , 1992; Iade cola, 1992) and inflammation (Granger et aI., 1990). NO is also an important factor in pathophysiologi cal events in brain. Recent studies have implicated alterations in cerebral NO levels with ischemic cell damage, particularly with glutamate neurotoxicity after cerebral ischemia (Garthwaite, 1991; Dawson et aI., 1991;Snyder and Bredt, 1992; Nowicki et aI. , 1991). Although NO is a subject of great interest in brain research, to our knowledge, direct in vivo measurements of NO in brain after ischemia have not been performed. NO is a reactive molecule, and 355level. Administration of N-nitro-L-arginine methyl ester (n = 4), an inhibitor of nitric oxide synthase, before onset of ischemia, maintained NO at basal levels. Our data in dicate that large increases in NO occur at onset of isch emia, which may affect tissue response to an ischemic insult. Key Words: Nitric oxide-Middle cerebral artery occlusion-Rat.it is therefore difficult to measure in vivo using stan dard chemical techniques. Here we report the first direct measurement of NO in rat brain during and after cerebral ischemia, using a NO sensitive por phyrinic microsensor . MATERIALS AND METHODSEight male Wistar rats (weighing 260--300 g) were anes thetized with 3.5% halothane for induction and 1% halo thane for maintenance, in a 3:1 N20/02 mixture. Four of the animals were administered a nitric oxide synthase in hibitor, L-NAME (N-nitro-L-arginine methyl ester; 30 mg! kg, i. v.), 15 min before induction of middle cerebral ar tery (MCA) occlusion. The femoral artery was cannulated to monitor arterial blood pressure and for sampling of blood gases. The rectal temperature was maintained at 37.0 ± i.O°C. MCA occlusion was induced for 2 h using a method of intraluminal vascular occlusion (Nagasawa and Kogure, 1989; Zea Longa et aI., 1989; Chen et aI., 1992a). Briefly, the right common carotid artery, external carotid artery, and internal carotid artery were isolated via a ven tral midline incision. The distal end of the external carotid artery was ligated with 5-0 silk suture at the branch of the occipital artery, and the origin of the external carotid ar tery was loosely tied with 5-0 silk suture. A microvascular clip was placed across the common carotid artery and internal carotid artery. A 5-cm length of 4-0 nylon mono filament, with its tip rounded by heating near ...

High polymers of ethylene oxide have been shown to have a number of unique properties in water solution. In this study, these properties have been investigated from the view of the behavior of large neutral molecules in media of high dielectric constant. Predictably, these high polymers of ethylene oxide undergo salting‐out effects which are reflected in changes of solution viscosity with salt concentration. Salts vary in effectiveness in a manner similar to that observed in the case of small neutral solute molecules. The salting‐out and viscosity effects are paralleled by the inverse solubility‐temperature relationship in water. Above a minimum molecular weight of about 50,000, the precipitation temperature (the temperature at which polymer separates from solution as a separate phase as the temperature is raised) becomes essentially independent of molecular weight. For these very high polymers the upper temperature limit of solubility in water is independent of polymer concentration over a wide range of concentration. These effects are discussed in terms of the balance of hydrophilic and hydrophobic character in the polymer structure which can be altered by increasing the hydrocarbon content of the polymer through copolymerization of ethylene oxide with other olefin oxides such as propylene oxide. This investigation permits the development of an interpretation of the unusual rheology of high molecular weight poly(ethylene oxide) in water solution.

SYWPS~Inveatigations of the properties of very high molecular weight polymers of ethylene oxide have shown that, while this polymer structure is relatively nonpolar, it displays a high degree of polymer solvent interaction in aqueous systems. A unique application of the hydrogen bonding affinity of the ether oxygens in the poly (ethylene oxide) chain has been found in the molecular aaeociation complexes formed between thh polyether and polymeric acids such as poly(acrylic acid). Interest in the properties of theae complexes

SynopsisEvidence is presented for the interaction of metal salts such as potassium iodide with polyethers such as poly(ethy1ene oxide). This interaction is sufficiently marked that the incorporation of 10-3001, of the salt in the bulk polymer markedly reduces crystallinity while retaining compatibility. Examination of electroviscons effects in methanol demonstrates that the salt-polymer adduct behaves as a typical polyelectrolyte a t low salt concentrations, while the polymer in absence of salt is essentially insoluble in methanol a t room temperature. Measurements of the equilibrium between salt and polymer along with a study of various molecular weight polymers strongly suggest that one salt molecule associates with about nine ethylene oxide units. It is proposed that the association is due to an ion-dipole interaction, and the anion is tentstively postulated as the species directly associating with the polymer. The association of other metal salts and other polymers are interpreted in this light. The significance of these results in interpreting salting-in phenomena is also discnssed.