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Biomedical subjects

E Shohami

Publications and source records attributed to E Shohami.

At least 127 records · Page 7Linked to original sources
PubMed1985

An ex vivo method for evaluating prostaglandin synthetase activity in cortical slices of mouse brain.

The release of prostaglandin E2 (PGE2) from cortical slices of mice into incubation medium is followed for 3 h and compared to PGE2 levels in the corresponding slice. Immediately after decapitation, the rate of PGE2 released into the incubation medium is elevated and a steady low rate of spontaneous release is gained within 1-2 h of incubation. PGE2 synthesis and release is blocked in a dose-dependent manner by either indomethacin (3 X 10(-6) -3 X 10(-4) M) or flufenamic acid (2.6 X 10(-6) M) either when added in vitro or administered in vivo. Full recovery of PGE2 synthesis is reached after 3 h incubation of slices following in vivo administration of indomethacin. In vivo administration of flufenamic acid results in prolonged inhibition of PGE2 released in vitro. The inhibition of PGE2 released by indomethacin is also correlated with the slice PGE2 content. Administration of lipopolysaccharide (LPS), a known activator of phospholipase A2, results in a fivefold increase in PGE2 and a twofold increase in 6-keto-PGF1 alpha released into the medium. The release of thromboxane B2 is not affected by LPS.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Intrathecal morphine induces myoclonic seizures in the rat.

The development of myoclonic activity as a toxic effect of morphine application into the intrathecal space in rats is described. This syndrome resembled the human syndrome of action myoclonus by its spontaneous onset and its augmentation by initiation of movement or by an acoustic stimulus. It was not reversed or prevented by naloxone. This effect of morphine was associated with an increase in serotonergic activity in the spinal cord and was reduced by pretreatment with parachlorophenylalanine in doses which reduced spinal 5-HT by approximately 60%. The dose which produced this syndrome was about ten times higher than the analgesic dose applied by the same route. Other commonly used opiates such as: methadone (0.5-2 mg/kg), pethidine (2-10 mg/kg), fentanyl (2-10 micrograms/kg) and ketamine (2-10 mg/kg) did not produce myoclonic-like activity, but methadone and pethidine at the highest doses caused respiratory arrest. Fentanyl appeared to be the safest of the drugs tested since a relatively high dose, administered into the intrathecal space did not cause any side effects, while morphine was least safe of the five drugs since it produced myoclonic activity in addition to the widely documented respiratory depression. We suggest that the production of the myoclonic activity is mediated by spinal serotonergic systems.

Analgesics↗
PubMed1984

Phenylethylamine, norepinephrine and mounting behavior in the male rat.

Phenylethylamine, which induces mounting behavior in naive adult male rats when administered chronically, was shown to selectively raise brain norepinephrine levels in the medial preoptic nucleus, a region known to be implicated in the regulation of sexual behaviors. It is suggested that the catecholamine alteration is a secondary response to the primary influence of phenylethylamine on the preoptic nucleus.

Animals↗
PubMed1984

Accumulation of prostacyclin in rat brain during haemorrhagic hypotension--possible role of PGI2 in autoregulation.

The effect of haemorrhagic hypotension on the levels of prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and 6-keto prostaglandin F1 alpha (6-keto-PGF1 alpha) in cortical tissue of rats was studied. Lightly anesthetized rats were subjected to steady-state hypotension for 15 min, with a mean arterial blood pressure of 80, 60, and 40 mm Hg, and compared to a control group of normotensive rats. No significant change was found in the levels of PGE2 and TXB2. The level of 6-keto-PGF1 alpha increased from 7.8 +/- 0.9 to 14.1 +/- 1.9 pg/mg protein (p less than 0.02) at 80 mm Hg. Our findings suggest that prostacyclin, which is a potent vasodilator, might play a role in setting the lower limit of the autoregulation range.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

Intracranial pressure during prolonged experimental convulsions in cats.

Experiments were carried out in cats to examine the relationship between prolonged convulsions and intracranial pressure. The convulsions were induced by pentylenetetrazole or bicuculline. Blood pressure, intracranial pressure and electroencephalogram were continuously monitored. Generalized tonic-clonic convulsions appeared with typical changes in the electroencephalogram 7-35 s after administration of the epileptogenic drugs. These convulsions persisted for 1-2 h. Concomitant with the clinical convulsions, intracranial pressure increased three- to fivefold, reaching maximal pressures of 20-94 mm Hg after 20-420s. The intracranial pressure remained high for between 47 s and 10 min, then began to fall gradually, reaching preictal levels after 2-30 min despite the continuation of convulsions. The variations in intracranial pressure were found to be independent of changes in blood pressure. The intracranial pressure, after dropping to preictal values, remained unchanged for up to 6 h after the induction of convulsions.

Animals↗
PubMed1983

Application of high-performance liquid chromatography with electrochemical detection to the determination of catecholamines in microdissected regions of the rat brain.

High-pressure liquid chromatography (HPLC) with electrochemical detection was applied for measurement of catecholamines in microdissected tissues from discrete brain regions. Brain areas were dissected, extracted and processed for HPLC assay without further purification. The advantage of this method is its simplicity and relatively low cost and may therefore be applied to the measurement of amines in brain micropunches.

Animals↗
PubMed1983

Hypersensitivity of morphine-tolerant rabbits to the respiratory stimulant effect of a cholinergic agonist.

The effect of morphine and oxotremorine, a centrally acting cholinergic agonist on the respiratory rate and arterial blood gases, was studied in rabbits given saline, increasing doses of morphine (5 mg/kg, 2 days; 10 mg/kg, 2 days; and 20 mg/kg, 3 days) injected at 12-hr intervals for 1 week. Care was taken to ensure that the chronically morphine-treated rabbits were neither under the influence of a previous dose of morphine nor in a phase of withdrawal when the response to test doses was measured. Tolerance to the respiratory depressant effect of morphine was demonstrated by the finding that a 5 times greater dose of morphine was needed to decrease respiration rate and raise arteriolar pCO2 than that given to saline-treated rabbits. The respiratory stimulant effect of oxotremorine, as demonstrated by an increase in respiration rate and decrease in PaCO2, was significantly greater in morphine-tolerant rabbits. It is concluded that chronic opiate treatment can induce supersensitivity of the cholinergic systems subserving control of respiration.

Animals↗
PubMed1982

Influence of blood glucose concentration on brain lactate accumulation during severe hypoxia and subsequent recovery of brain energy metabolism.

The effects of hypoxaemia on regional cerebral blood flow (CBF) and brain cortical metabolite concentrations were investigated at different blood glucose concentrations in rats under nitrous oxide anaesthesia. Tissue hypoxia of 15-min duration was induced by a combination of arterial hypoxaemia, hypotension, and clamping of the right carotid artery. Blood glucose concentrations were manipulated by varying the food intake in the 24 h before the experiment, and by glucose administration. Cortical CBF doubled during hypoxia on the intact side, but did not differ significantly from control values on the clamped side. In the clamped hemisphere there was a substantial decrease in adenylate energy charge. At brain tissue glucose concentration of 1 mumol g-1 and above, there was an inverse correlation between adenylate energy charge and brain lactate concentration. In starved animals with mean brain glucose of 0.32 +/- 0.00 mumol g-1, lactate concentration was significantly lower, in spite of equally severe disruption of energy state. Recovery of brain adenylate energy charge was worse in fed and glucose-infused groups than in the fasted group. These results demonstrate that limitation of substrate supply during severe hypoxia in the rat allows enhanced recovery of brain energy metabolism following the hypoxic episode.

Animals↗
PubMed1980

S-substituted derivatives of 6-mercaptopurine ribosides interact both with the transport and metabolic phosphorylation of uridine by virus-transformed hamster fibroblasts.

The uptake of uridine by mammalian cells consists of transport of uridine across the plasma membrane followed by its metabolic conversion, mainly by phosphorylation. S-substituted aromatic derivatives of 6-mercaptopurine ribosides are potent inhibitors of the nucleoside uptake systems in human erythrocytes and in mammalian cells in culture and have been studied extensively. We present here a theoretical analysis which enables one to decide whether transport of metabolites, their metabolic trapping within the cell, or both, are susceptible to inhibition. This analysis was applied in the study of the effect of some inhibitors on uridine and cytosine-beta-D-arabinoside uptake by transformed Nil-8 cells. It was found that in Nil-SV cells, both transport and metabolic conversion are susceptible to inhibition by nitrobenzylmercaptoinosine and by dansylaminoethylmercaptoguanosine. Nitrobenzylmercaptoinosine displays inhibition constants of 20 and 7 nM for transport and phosphorylation, respectively, while for dansylaminoethylmercaptoguanosine the inhibition constants are 1.8 and 0.6 microM, respectively, for the same processes. Cytosine-beta-D-arabinoside is a synthetic nucleoside which is not metabolizable in Nil cells. Its uptake properties are determined by the transport mechanism alone. The transport of this nucleoside into Nil-SV cells in inhibited by nitrobenzylmercaptoinosine and the inhibition constant found is approx. 5 times greater than that for uridine.

Animals↗
PubMed1979

A kinetic analysis of the uptake of cytosine-beta-D-arabinoside by rat-B77 cells. Differentiation between transport and phosphorylation.

We present here a differentiation by kinetic methods of the tandem processes of transport and metabolic during uptake of cytosine-beta-D-arabinoside by intact rat fibroblasts. Transport across the cell membrane occurs by a carrier-mediated mechanism displaying a Km of approximately 500 microM and a V of approximately pmol x min-1 x (10(6) cells)-1. The subsequent metabolic trapping (phosphorylation) has a Km of approximately 15 microM and V of approximately 0.25 pmol x min-1 x (10(6) cells)-1. In this system, transport is rate-limiting for the first phase of the uptake process whereas phosphorylation becomes rate-limiting when internal concentration of radioactive labeled substrate exceeds that in the extracellular medium. The duration of the first phase depends on the substrate concentration.

Animals↗
PubMed1979

S-(N-dansylaminoethyl)-6-mercaptoguanosine as a fluorescent probe for the uridine transport system in human erythrocytes.

A fluorescent derivative of 6-mercaptoguanosine, S-(N-dansylaminoethyl)-6-mercaptoguanosine, was synthesized, and found to be a strong inhibitor of the uridine transport system of erythrocyte (Ki approximately 0.3 microM). The emission spectrum of this compound has peaks at 400 and 550 nm. The emission at 550, but not that a 400 nm, in environment-sensitive. A method was devised for preparing a suspension of erythrocyte-membrane fragments with sufficiently low light scattering so that a detailed study could be made of the fluorescence of the probe when bound to membranes. Direct binding measurements showed the existence of a tight binding site, with a dissociation constant of the same order of magnitude as the inhibition constant. Binding of probe and substrate are not mutually exclusive, but the fluorescence and affinity of the bound probe are sensitive to the presence of uridine. The emission spectrum suggests that the bound probe penetrates into the bilayer region of the membrane.

Binding Sites↗
PubMed1978

Nucleoside transport in mammalian cell membranes. IV. Organomercurials and organomercurial-mercaptonucleoside complexes as probes for nucleoside transport systems in hamster cells.

Organomercurials form stable stoichiometric complexes with thiolated nucleosides. The complexes inhibited uptake of ribonucleosides and cytosine arabinoside (CAR) in various types of normal and transformed cells. The inhibition was competitive and reversible (Ki = 3--6 micrometer). The interaction between complexes and transport system displayed a 1:1 stoichiometry. Chemical factors which contributed to the inhibitory power were evaluated with a series of S-alkylated derivatives and S--Hg--R complexes of mercaptonucleosides. The inhibitory potency was not determined exclusively by the hydrophobic nature of either the S-alkylated or the S--Hg--R moieties. Chemical modification of cells with penetrating and nonpenetrating organomercurials lead to stimulation of nucleoside uptake and to an increase in its susceptibility to inhibition by S--Hg--R complexes or S-aklylated derivatives of mercaptopurine ribosides. The kinetic and chemical data obtained with nucleoside analogs and with chemical modifiers suggested complex features of nucleoside transport systems. Four distinct classes of sites were implied: (i) a substrate binding site susceptible directly to competitive inhibition by organomercurial-mercaptonucleoside complexes, (ii) an additional site susceptible either to S-arylalkylated or S-mercuriated derivatives of 6-mercaptopurine ribosides, (iii) SH-containing modifier sites which stimulate uridine uptake upon binding of organomercurials, and (iv) SH-containing modifier sites which inhibit the function upon binding of organomercurials. From the observation that only SH sites related to stimulation were susceptible to modification by macromolecular-SH modifier probes, some conclusions can be drawn regarding the disposition of the various sites in the cell membrane in general and among membrane components in particular.

Binding, Competitive↗
PubMed1973

Relation between the dielectric constant of hydrophobic cation exchange membrane and membrane permeability to counterions.

Filters made of cellulose acetate-nitrate when saturated with organic solvents and interposed between aqueous solutions form membranes which behave like cation exchangers. The diffusion coefficients of counterions in such membranes are strongly dependent upon the dielectric constant of the saturating solvent. The results obtained suggest that a linear relationship between the log of the cation's diffusion coefficient (or membrane conductance) and the reciprocal value of the dielectric constant of the saturating solvent exists. There is also a good correlation between the relative membrane permeability to organic cations and the solubility of the cations in the pure solvent phase. These studies indicate that there are two routes for cation movement through the membrane: (a) the bulk hydrophobic phase and (b) continuous narrow aqueous channels.

Cations, Monovalent↗
PubMed1973

Model hydrophobic ion exchange membrane.

Two models of hydrophobic ion exchange membranes were examined theoretically with regard to the characteristics of cellulose acetate-nitrate membranes saturated with hydrophobic solvents. The first model, consisting of fixed negative sites dispersed in a homogeneous medium of low dielectric constant, was shown to be invalid for the experimental membranes. The second model, consisting of fixed negative sites in an aqueous channel surrounded by a medium of low dielectric constant, explains many properties of the cellulose acetate-nitrate hydrophobic membranes and was analyzed in some detail. Organic cations can enter the membranes through the hydrophobic phase as well as through the aqueous channels. The mechanism of counterion movement in such a model is assumed to consist of exchange of vacancies and or double-occupied sites positions. The presence of the medium of low dielectric constant around the aqueous channel increases the "self"-energy of the ions in the channel and the electrostatic interaction between a fixed site and a counterion in the membrane. Both these factors can account for the marked dependence of ion mobility in the aqueous channels on the dielectric constant of the surrounding medium. The model predicts membrane preference for monovalent counterions over divalent ones.

Capillary Action↗