In vitro effects of thyroid hormones on ectonucleotidase activities in synaptosomes from hippocampus of rats.
1. Studies have shown that adenosine transport and adenosine A1 receptors in rat brain are subjected to regulation by thyroid hormone levels. Since the ectonucleotidase pathway is an important source of adenosine extracellular, in the present study the in vitro action of T3 and T4 hormones on ectonucleotidase activities in hippocampal synaptosomes was evaluated. 2. T3 (Triiodo-l-thyronine) significantly inhibited, in an uncompetitive manner, the ATP and ADP hydrolysis promoted by ATP diphosphohydrolase activity in hippocampal synaptosomes of adult rats. 3. In contrast, T4 (Thyroxine) only inhibited ATP hydrolysis in an uncompetitive mechanism, at the concentrations tested (100-500 microM), but at the same time did not affect ADP hydrolysis. 4. In the present study, we also investigate the in vitro effect of T3 and T4 on 5'-nucleotidase activity. However, there are no changes in the activity of this enzyme in the presence of T3 and T4 in the hippocampal synaptosomes of rats. 5. These results suggest that thyroid hormones could be involved in the regulation of ectonucleotidase activities, such as ecto-ATP diphosphohydrolase and ecto-ATPase, possibly exerting a modulatory role in extracellular adenosine levels.
Matos
José Alfredo de Aguiar
JA
Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil.
Bruno
Alessandra Nejar
AN
Oses
Jean Pierre
JP
Bonan
Carla Denise
CD
Battastini
Ana Maria Oliveira
AM
Barreto-Chaves
Maria Luiza M
ML
Sarkis
João José Freitas
JJ
D000241:Adenosine / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000201:enzymology*; D006868:Hydrolysis / Q000187:drug effects; D008297:Male; D017729:Presynaptic Terminals / Q000187:drug effects / Q000201:enzymology*; D011755:Pyrophosphatases / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D013961:Thyroid Gland / Q000378:metabolism*; D013963:Thyroid Hormones / Q000378:metabolism* / Q000494:pharmacology; D013974:Thyroxine / Q000378:metabolism / Q000494:pharmacology; D014284:Triiodothyronine / Q000378:metabolism / Q000494:pharmacology
D013963:Thyroid Hormones; D014284:Triiodothyronine; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D011755:Pyrophosphatases; C092064:ectonucleotide pyrophosphohydrolase; D000241:Adenosine; D013974:Thyroxine