Abstract
Adult Wistar male rats in a thyrotoxic state T4↑ rats) induced by administration of
T4 (350 µg/kg/day, i.p. for 7 days) as well as their euthyroid controls were submitted
to immobilization stress during forty minutes. Prolactin (PRL) secretion during stress
was significantly lower in T4↑ rats as compared to control animals. Treatment with
MK 212, a serotoninergic agonist, entirely reverts this situation. The effect of MK
212 seems to be due to its interaction with 5-HT2 receptors since it is blocked by LY 53857, a selective 5-HT2 antagonist. Furthermore, the blockade of 5-HT2 receptors by LY 53857, a selective 5-HT2 antagonist, significantly diminishes prolactin (PRL) response to stress in euthyroid
rats but has no effect in T4↑ animals. It is suggested that an increased concentration
of thyroid hormone in plasma disrupts an endogenous serotoninergic brain input necessary
to trigger stress-induced PRL rise.
Key words
Thyroid Gland - Prolactin - Serotonin - Stress
