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Alterations at brain A, adenosine receptors, adenosine metabolising enzymes and adenylate cyclase in hypothyroidism

Mazurkiewicz, Dorota; (1990) Alterations at brain A, adenosine receptors, adenosine metabolising enzymes and adenylate cyclase in hypothyroidism. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Rat brain tissue was used to study alterations at adenosine A1 receptors, in adenosine metabolising enzymes and adenylate cyclase in hypothyroidism. Rats were made hypothyroid by treatment with propylthiouracil and a low iodine diet for four weeks. Brain synaptic membranes were isolated from synaptosomes after fractionation on Ficoll gradients. Saturation binding analysis of the synaptic A1 adenosine receptor was performed using the agonist [3H] phenylisopropyladenosine (PIA), whilst competition binding analysis was performed using [3H] diethylphenylxanthine ([3H] DPX) as the radiogland and PIA as the competing ligand. Hypothroidism resulted in a significant decrease in [3H] PIA maximum binding, and of [3H] DPX maximum binding in the presence of GTP. No significant differences in the dissociation contants were found in either case. Measurements of adenylate cyclase activity revealed an enhanced inhibition of forskolin stimulated adenylate cyclase by PIA. Forskolin activation was comparable in euthyroid and hypothyroid states. Inhibition of adenylate cyclase by GTP was also comparable in euthyroid and hypothyroid states, although hypothyroidism impaired the inhibitory action of sodium on forskolin stimulated adenylate cyclase. The adenosine metabolising enzymes were assayed in extracts from six regions of rat brain namely the cortex, cerebellum, medula oblongata, striatum, hippocampus and hypothalamus. Adenosine deaminase and adenosine kinase were assayed in a supernatant fraction, whilst 5'- nucleotidase was assayed in myelin and synaptic membrane fractions. The three fractions were prepared by a combination of density centrifugation and Ficoll gradients. Hypothyroidism resulted in an increase in 5'-nucleotidase activity in the cerebullum, cortex, hippocampus and striatum; only the medulla oblongata showed an increase in myelin 5'-nucleotidase activity. Conversely a decrease in adenosine kinase activity was seen in the cerebellum, hippocampus, hypothalamus and striatum, whilst adenosine deaminase displayed no change in any of the six rat brain supernatant fractions studied.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Alterations at brain A, adenosine receptors, adenosine metabolising enzymes and adenylate cyclase in hypothyroidism
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
URI: https://discovery.ucl.ac.uk/id/eprint/10120946
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