T₃ Reverses the Changes in Met-Enkephalin and β-Endorphin Contents in the Anterior Lobe, But Not the Neuro-Intermediate Lobe of the Pituitary of Rats Rendered Hypothyroid by PTU-Treatment

Summary

The changes in met-enkephalin and β-endorphin contents in the pituitary in PTU-induced hypothyroidism were studied in the rat. After 2 weeks of PTU-treatment, both IR-met-enkephalin and IR-β-endorphin contents in the pituitary were significantly reduced. Gel filtration chromatography followed by radioimmunoassay showed that the immunoactivities in the peaks of precursors, met-enkephalin, β-lipotropin and β-endorphin were all lower in the pituitaries from the PTU-treated rats. In another experiment, some of the PTU-treated rats were injected daily with 500 μg T₃/kg b.w. In the hypothyroid rats, IR-met-enkephalin and IR-β-endorphin contents were decreased in both the anterior and neuro-intermediate lobes. Only the changes in the anterior lobe were reversed by T₃ treatment. In conclusion, while the effects on the anterior lobe are probably due to a deficiency in thyroid hormones, the mechanism for the decrease of opioid peptide contents in the neuro-intermediate lobe is still unclear.

Key-Words

Rat - PTU - Hypothyroidism - Pituitary - Met-Enkephalin - β-Endorphin