title: Secretion of 3,3'-diiodothyronine by the perfused canine thyroid isolated in situ.
abstract: Previous studies employing perfused dog thyroid lobes have shown that thyroidal secretion is modulated by intrathyroidal deiodination of T4 to T3 and rT3. To characterize further the intrathyroidal iodothyronine-deiodinating processes 3,3'-diiodothyronine (3,3'-T2) and T4 were measured in hydrolysate and effluent from isolated dog thyroid lobes during single passage perfusion with a synthetic hormone-free-medium. In five experiments the concentrations in effluent from unstimulated thyroid lobes were: 3,3'-T2, 208 +/- 62 pmol/liter; and T4, 12.8 +/- 2.8 nmol/liter (mean +/- SE). During the infusion of 100 microU/ml TSH, there was a parallel increase in the secreton of 3,3'-T2 and T4. After approximately 90 min of TSH infusion, effluent concentrations were: 3,3'-T2, 2490 +/- 420 pmol/liter; and T4, 204 +/- 24 nmol/liter. In a pronase hydrolysate of the thyroid lobes, the amounts were: 3,3'-T2, 2.44 +/- 0.56 pmol/mg; and T4, 1070 +/- 125 pmol/mg. Expressed as a percent of T4, the amount of 3,3'-T2 in thyroid effluent was approximately 10 times higher than that in thyroid hydrolysate. This relative hypersecrection of 3,3'-T2 was abolished by the infusion of 10(-3) or 10(-5) M propylthiouracil, an inhibitor of peripheral and intrathyroidal iodothyronine deiodination. Thus, thyroid secretion contains small amounts of 3,3'-T2, most of which seems to originate from intrathyroidal deiodination of T3 and/or rT3.
mesh_terms: D000818:Animals; D004104:Diiodothyronines / Q000378:metabolism*; D004285:Dogs; D066298:In Vitro Techniques; D010477:Perfusion; D011441:Propylthiouracil / Q000494:pharmacology; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D013970:Thyronines / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology; D013974:Thyroxine / Q000378:metabolism
chemical_list: D004104:Diiodothyronines; D013970:Thyronines; C030629:3,3'-diiodothyronine; D011441:Propylthiouracil; D013972:Thyrotropin; D013974:Thyroxine