Influence of the pineal gland on hypothalamic content of TRH in the Syrian hamster.

Blinding adult female hamsters by bilateral orbital enucleation caused an increase in thyrotropin-releasing hormone (TRH) content of the medial basal hypothalamus and also led to an increase in TRH content in the remainder of the hypothalamus (dorsal hypothalamus). Although pinealectomy by itself had no significant effect on the neuroendocrine-thyroid axis, this surgical procedure prevented the inhibition of serum thyroxin observed in blinded hamsters. Pinealectomy also prevented the increase in TRH content of medial basal and dorsal hypothalamus observed in blinded hamsters. The results are consistent with the view that the pineal gland has a CNS site of action and provide evidence that the anti-thyroid influence of the pineal gland can be explained by pineal inhibition of TRH release.