Thyroid hormones modulate both adenosine transport and adenosine A1 receptors in rat brain
Fideu, M.D.; Arce, A.; Esquifino, A.I.; Miras-Portugal, M.T.
American Journal of Physiology 267(6 Pt 1): C1651-C1656
1994
ISSN/ISBN: 0002-9513 PMID: 7810607 Document Number: 439086
Adenosine transport and adenosine A-1 receptors in rat brain are subjected to regulation by thyroid hormone levels. The studies were carried out with brain stem synaptosomal preparations from rat brain in euthyroid and various hypothyroid situations. The maximum velocity of the nitrobenzylthioinosine (NBTI)-sensitive adenosine transport was 3.3 +- 0.3 pmol cntdot mg protein-1 cntdot s-1 euthyroid rats. The transport in 1-wk thyroidectomized rats was decreased by 45.8% with respect to controls. No changes were found in the affinity of euthyroid and hypothyroid rats, with the Michaelis-Menten constant values equal to 1.9 +- 0.9 and 2.0 +- 0.5 mu-M, respectively. The transporter number measured by NBTI binding also decreased; the maximum binding capacity (B-max) was 112.9 +- 21.9 and 31.3 +- 4.1 fmol/mg protein for euthyroid and hypothyroid rats, respectively. The adenosine A-1 receptors were measured in synaptosomal membrane preparations in the presence of 100 mu-M guanosine-5'-O-3-thiotriphosphate for cylopenthyl-1,3-dipropylxanthine 8-(dipropyl 2,3-3H(N))((3H)DPCPX) binding. In euthyroid rats, the B-max value was 227.6 +- 27.6 fmol/mg protein, a significant decrease of 23% was obtained in 1-wk hypothyroid rats. In all other thyroid situations studied, adenosine transport capacity, adenosine transporter number, and adenosine A-1 receptor number were restored to control levels.