title: Thyroid hormones regulate the formation of inositol phosphate in response to thyrotropin-releasing hormone in rat anterior pituitaries.
abstract: 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.
authors.affiliation: First Department of Internal Medicine, Gunma University School of Medicine, Maebashi, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Iriuchijima
authors.forename: T
authors.initials: T
authors.lastname: Michimata
authors.forename: K
authors.initials: K
authors.lastname: Miyashita
authors.forename: T
authors.initials: T
authors.lastname: Ogiwara
authors.forename: M
authors.initials: M
authors.lastname: Yamada
authors.forename: M
authors.initials: M
authors.lastname: Murakami
authors.forename: M
authors.initials: M
authors.lastname: Mori
mesh_terms: 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
chemical_list: D007295:Inositol Phosphates; D013963:Thyroid Hormones; D014284:Triiodothyronine; D014316:Tritium; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D013974:Thyroxine