Effects of TSH on cAMP levels and thyroid hormone release in human thyroid 'autonomous' nodules: relationship with iodothyronine and iodine content in thyroglobulin.
The effect of TSH on the adenylate cyclase-cAMP system and in vitro iodothyronine release, together with the iodothyronine and iodine content of 19s thyroglobulin, were studied in seven clinically euthyroid patients with autonomous thyroid nodules. Basal cAMP and cGMP content together with phosphodiesterase and protein-kinase activities were normal in nodular, and suppressed in extranodular tissue. TSH-dependent cAMP accumulation was reduced in nodular tissue, but normal in the suppressed extranodular tissue. In vitro TSH-dependent iodothyronine release from nodular and extranodular tissue was absent. Thyroxine and iodine content of thyroglobulin extracted from nodular tissue was reduced, while triiodothyronine content was normal but with a low T4/T3 ratio. In extranodular tissue T3, T4 and iodine contents were reduced. In conclusion, autonomous thyroid nodules produced a poorly iodinated thyroglobulin leading to preferential T3 secretion with increased circulating free thyroid hormones even in clinically euthyroid patients.
D000328:Adult; D000242:Cyclic AMP / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007455:Iodine / Q000032:analysis; D008297:Male; D008875:Middle Aged; D013954:Thyroglobulin / Q000378:metabolism; D013959:Thyroid Diseases / Q000378:metabolism* / Q000503:physiopathology; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism; D013972:Thyrotropin / Q000494:pharmacology*; D013974:Thyroxine / Q000032:analysis / Q000378:metabolism*; D014284:Triiodothyronine / Q000032:analysis / Q000378:metabolism*
D014284:Triiodothyronine; D013972:Thyrotropin; D013954:Thyroglobulin; D007455:Iodine; D000242:Cyclic AMP; D006152:Cyclic GMP; D013974:Thyroxine