Dana Jamieson

Comparison of Oxygen Tensions in Normal Tissues and Yoshida Sarcoma of the Rat Breathing Air or Oxygen at 4 Atmospheres

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Studies of mechanisms of chemical radiation protection in vivo. 3. Changes in fluorescence of intracellular pyridine nucleotides and modification by extracellular hypoxia.

SummaryChanges in the fluorescent signal emitted by the pyridine nucleotide co-enzyme system were recorded from rat tissues in vivo and from ascites tumour cells in vitro. The degree of reduction of this component of the electron transport chain has been shown to be a sensitive index of intracellular oxygen tensions. The effect of selected radioprotective chemicals on the fluorescent emission signal has been studied in rats respiring oxygen at pressures from zero to 760 mm Hg. Similar observations for changes in pO2 have been made for ascites cells treated with protective agents. A quantitative analysis has been made of the redox state of this respiratory co-enzyme system.Results obtained support the view that the radioprotective action of the sulphydryl derivatives, cysteamine and AET (and possibly cystamine and cysteine) is independent of intracellular tissue pO2 levels. That of dimethyl sulphoxide appeared similarly independent of pO2 change. Results with 5-hydroxytryptamine were equivocal. The agents ...

POSSIBLE MEDIATORS OF THE WRITHING RESPONSE INDUCED BY ACETIC ACID OR PHENYLBENZOQUINONE IN MICE

Despite widespread use of the writhing response to phenylbenzoquinone or acetic acid injection in mice as a screen for analgesic activity, possible mediators of this response remain unidentified.

Ligand-binding and pharmacological studies on dopamine and octopamine receptors in the heart of the bivalve mollusc, Tapes watlingi

Abstract 1. Pharmacological and ligand binding studies have been carried out on the dopamine receptors of the isolated beating heart and on heart homogenate preparations of Tapes watlingi. 2. Dopamine has both an excitatory and an inhibitory action on the isolated, spontaneously beating T. watlingi heart. Receptors mediating these actions are distinct from those for 5-hydroxytryptamine and acetylcholine. Octopamine has a purely excitatory action. 3. High affinity binding of [3H]dopamine to heart membranes has been shown. Displacement of 10 nM [3H]dopamine by unlabelled dopamine in the range 5–2,000 nM gives complex displacement curves, suggesting the presence of at least two dopamine receptor populations. 4. In the binding assay, concentrations of octopamine lower than 1 nM can displace a significant proportion of [3H]dopamine, in contrast to its lack of effect in displacing DA∗ from mammalian striatal receptors. This is interesting in view of the fact that experiments on the isolated heart using a wide range of drugs failed to differentiate octopamine excitatory responses and dopamine inhibitory responses. 5. Results of comparative ligand binding studies suggest sufficient similarity between dopamine receptors in T. watlingi heart and mammalian brain to make this marine preparation useful in screens for dopaminergic drugs.

Comparison of the bronchodilator and vasodilator activity of sodium azide and sodium nitroprusside in the guinea‐pig

1. Sodium azide and sodium nitroprusside are potent dilators of the intact guinea‐pig tracheal preparation in vitro.

Energy metabolism of the heart of the mollusc Tapes watlingi

Abstract 1. 1. Metabolic inhibitors, anoxia and measurement of oxygen consumption have been used to study the energy metabolism associated with the contractile process of the isolated heart of the bivalve mollusc, Tapes watlingi. 2. 2. In this tissue oxidative phosphorylation is used as an energy source for spontaneous contractions, however, if oxygen is removed the tissue is able to metabolize anaerobically and thus maintain near optimal activity. 3. 3. Glycolysis is important in maintaining energy demands for contraction of T. watlingi hearts, for in aerated medium and in the presence of glycolytic inhibitors the activity gradually decreases to about half the control value. 4. 4. The mollusc heart is more adaptable than mammalian tissue in utilizing alternate metabolic pathways to maintain energy production.

Effect of Progressive Changes in Body Temperature of Rats on Tissue Oxygen-tensions, in Relation to Radiosensitivity

SummaryOxygen-tensions, measured polarographically in tissues of rats subjected to progressive hypothermia and hyperthermia, are reported. Corresponding radiosensitivity values have been estimated and indicate that both hypothermia (15°c) and hyperthermia (41°c) cause radioprotection due to ‘oxygen effect’, with a reduction in radiosensitivity of haemopoietic tissues to ∼ 75 per cent and ∼ 85 per cent of maximum values respectively. The physiological reasons for these findings are discussed.

Inhibition of nerve-mediated contractions in isolated guinea-pig ileum by 1-methylisoguanosine, a novel purine from a sponge.

1-Methylisoguanosine, a novel purine isolated from the sponge Tedania digitata (Schmidt) selectively inhibited contractions produced by nerve stimulation in the guinea-pig ileum but was without effect on contractions produced by acetylcholine or histamine. The ED50 for inhibition of nicotine responses or responses to submaximal transmural stimulation was 1.1 mumoles/l. The inhibition of nerve-mediated contractions appeared to be due to inhibition of transmitter release from nerve endings in the ileum, as has been suggested for the action of adenosine. Theophylline antagonized the action of 1-methylisoguanosine and overall the results suggest that 1-methyl-isoguanosine acts at an adenosine receptor in the guinea-pig ileum, but is approximately ten times more potent than adenosine itself. A series of related purines which were resistant to the action of adenosine deaminase were also tested for their effect on the nerve-mediated contractions of guinea-pig ileum and the results compared with the in vivo effect on muscle relaxation in mice. All active purines tested produced results qualitatively similar to those of 1-methylisoguanosine itself.

Anticonvulsant activity of farnesylacetone epoxide--a novel marine natural product.

A marine natural product, farnesylacetone epoxide, which is chemically related to juvenile hormone, has anticonvulsant properties at nonsedative doses in mice.

Non-specific stimulant activity of tyramine on isolated intestinal preparations

The effect of tyramine on isolated organ preparations from several animal species has been studied. Contraction of the guinea-pig ileum by tyramine is due to a direct effect on histamine receptors whereas the contractile effect on the rat fundus and rabbit jejunum by tyramine is mediated through 5-hydroxytryptamine receptors. These studies indicate the variability and non-specificity of isolated organ responses and that the effects of tyramine are not limited to adrenergic systems.