title: Thyroid hormone inhibition of phosphatidylinositol-specific phospholipase C in rat liver.
abstract: We investigated the effect of thyroid hormone on phosphatidylinositol-specific phospholipase C activity in rat liver. Thyroidectomy increased the activity of the enzyme. Thyroid hormone (T4, 40 micrograms) administration to thyroidectomized-rats decreased phospholipase C activity. The inhibition induced by thyroid hormone was of a non-competitive type. The higher concentration of Ca2+ strongly inhibited the activity of the enzyme obtained from thyroidectomized-rats' liver in vitro. The diminished activity of the enzyme obtained from thyroxine-treated-thyroidectomized-rats was recovered by pretreatment of the enzyme with EGTA. The activity of the enzyme derived from thyroidectomized-rats was not affected by EGTA treatment. These results suggest that thyroid hormone decreases the activity of phosphatidylinositol-specific phospholipase C activity through the mobilization of Ca2+ in the intracellular space.
mesh_terms: D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D004533:Egtazic Acid / Q000494:pharmacology; D008099:Liver / Q000201:enzymology*; D008297:Male; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010726:Phosphodiesterase Inhibitors; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases; D051381:Rats; D011919:Rats, Inbred Strains; D013965:Thyroidectomy; D013974:Thyroxine / Q000009:adverse effects* / Q000097:blood / Q000494:pharmacology; D014284:Triiodothyronine / Q000097:blood
chemical_list: D010726:Phosphodiesterase Inhibitors; D014284:Triiodothyronine; D004533:Egtazic Acid; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D013974:Thyroxine; D002118:Calcium