The presence of severe neurological symptoms in
thyroid diseases has highlighted the importance of
thyroid hormones in the normal functioning of the mature brain. Since,
ATP is an important excitatory
neurotransmitter and
adenosine acts as a neuromodulatory structure inhibiting
neurotransmitters release in the central nervous system (CNS), the ectonucleotidase cascade that hydrolyzes
ATP to
adenosine, is also involved in the control of brain functions. Thus, we investigated the influence of hyper-and
hypothyroidism on the
ATP,
ADP and
AMP hydrolysis in hippocampal and cortical slices from adult rats.
Hyperthyroidism was induced by daily
injections of
l-thyroxine (T4) 25 microg/100 g
body weight, for 14 days.
Hypothyroidism was induced by
thyroidectomy and
methimazole (0.05%) added to their
drinking water for 14 days. Hypothyroid rats were hormonally replaced by daily
injections of T4 (5 microg/100 g
body weight, i.p.) for 5 days.
Hyperthyroidism significantly inhibited the
ATP,
ADP and
AMP hydrolysis in hippocampal slices. In brain cortical slices,
hyperthyroidism inhibited the
AMP hydrolysis. In contrast,
hypothyroidism increased the
ATP,
ADP and
AMP hydrolysis in both hippocampal and cortical slices and these effects were reverted by T4 replacement. Furthermore,
hypothyroidism increased the expression of
NTPDase1 and
5'-nucleotidase, whereas
hyperthyroidism decreased the expression of
5'-nucleotidase in hippocampus of adult rats. These findings demonstrate that thyroid disorders may influence the
enzymes involved in the complete degradation of
ATP to
adenosine and possibly affects the responses mediated by
adenine nucleotides in the CNS of adult rats.