Thyrotrophin increases the alpha 1b-adrenergic receptors in rat thyroid gland in vivo.
Using chlorethylclonidine (CEC), an alpha 1b-adrenergic receptor-selective antagonist, we characterized alpha 1-adrenoceptor subtypes in rat thyroid gland, and investigated the effect of methimazole (MMI)-induced high TSH levels on alpha 1 receptor subtypes and noradrenaline-induced iodide organification. The density of thyroid alpha 1-adrenergic receptors was increased about sixfold in rats treated with MMI for 3 weeks compared with controls. Pretreatment of thyroid membrane preparations with CEC (10 mumol/l) caused an 83% decrease in specific 2-[beta-(hydroxy-3-[125I]iodophenyl) ethylaminomethyl]tetralone binding sites in MMI-treated rats, but only a 43% decrease in control rats. The density of CEC-insensitive alpha 1 receptors (alpha 1a) was similar in MMI-treated and control rats, so MMI was shown to increase CEC-sensitive alpha 1 receptors (alpha 1b). Noradrenaline-stimulated iodide organification was threefold greater in MMI-treated rats than in control rats when values were expressed as a per cent increase over basal levels. Pretreatment of thyroid lobes with 10 mumol CEC/l for 30 min caused a 66% decrease in maximal noradrenaline-induced iodide organification in MMI-treated rats, but a significantly lower decrease (49%) in control rats. These results suggest that the rat thyroid gland contains both alpha 1a and alpha 1b receptors, both of which mediate noradrenaline-induced iodide organification, and also that TSH enhances noradrenaline-induced iodide organification by increasing alpha 1b receptor density.
Shimura
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H
Third Department of Internal Medicine, University of Yamanashi Medical School, Japan.
Endo
T
T
Onaya
T
T
D000317:Adrenergic alpha-Antagonists / Q000378:metabolism; D000818:Animals; D003000:Clonidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D007454:Iodides / Q000378:metabolism; D008297:Male; D008713:Methimazole / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D009929:Organ Size / Q000187:drug effects; D010627:Phenethylamines / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D044024:Tetralones; D013961:Thyroid Gland / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D000317:Adrenergic alpha-Antagonists; D007454:Iodides; D010627:Phenethylamines; D011942:Receptors, Adrenergic, alpha; D044024:Tetralones; D014284:Triiodothyronine; C051731:chlorethylclonidine; C010652:BE 2254; D008713:Methimazole; D013972:Thyrotropin; D003000:Clonidine; D013974:Thyroxine; D009638:Norepinephrine