Thyroid hormones regulate the formation of inositol phosphate in response to thyrotropin-releasing hormone in rat anterior pituitaries.
The effects of thyroid hormones on TSH secretion and inositol phospholipid hydrolysis in response to thyrotropin-releasing hormone (TRH) in rat anterior pituitaries were examined. Experimental hypothyroidism caused a significant increase in [3H]inositol phosphate ([3H]IP) formation in response to TRH in rat anterior pituitaries with a concomitant elevation of blood TSH. In contrast, administration of thyroxine (T4) to hypothyroid rats resulted in a complete restoration of blood TSH and TRH-stimulated [3H]IP formation to the euthyroid control value. Furthermore, in vitro pre-treatment of anterior pituitaries with triiodothyronine (T3) produced a dose-dependent decrease in both TSH secretion and the formation of [3H]IP in response to TRH. These results indicate that thyroid hormones regulate TRH receptor-linked inositol phospholipid hydrolysis in the rat anterior pituitary, suggesting that negative feedback action of thyroid hormone occurs at post receptor event in the rat anterior pituitary, which may, to a certain extent, be responsible for the underlying mechanism of T3 inhibition of TSH secretion.
Iriuchijima
T
T
First Department of Internal Medicine, Gunma University School of Medicine, Maebashi, Japan.
Michimata
T
T
Miyashita
K
K
Ogiwara
T
T
Yamada
M
M
Murakami
M
M
Mori
M
M
D000818:Animals; D006868:Hydrolysis; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000096:biosynthesis*; D008297:Male; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013963:Thyroid Hormones / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000502:physiology; D013974:Thyroxine / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology; D014316:Tritium
D007295:Inositol Phosphates; D013963:Thyroid Hormones; D014284:Triiodothyronine; D014316:Tritium; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D013974:Thyroxine