title: Defects in intrathyroid binding of iodine and the perchlorate discharge test.
abstract: The kinetics of [123I]iodide uptake were studied when organification of iodine by the thyroid gland was normal and when this binding function was diminished by drugs or disease. Each study was terminated by a sodium perchlorate discharge test (300--600 mg iv) at 60 min or, in some cases, 10--30 min. The results confirmed that binding takes place rapidly in the uninhibited gland with the binding rate constant being at least 0.150 min-1. Discharge from the uninhibited gland is less than 3.5% of the gland uptake when perchlorate is given 60 min after the radioiodide. Subjects with an intrinsic binding defect manifested discharges of 11% of greater of the 60 min uptake and the estimated binding rate constants ranged from 0.003--0.057 min-1. Thyrotoxic subjects receiving 5 mg carbimazole twice daily manifested discharges ranging from 5.4--64.2%, and in those receiving 20 mg twice daily the observed discharges were 67.6--94.6% of the 60 min uptake. The study shows that a correctly performed perchlorate discharge test will detect minimal inhibition of iodine binding. An important factor is the duration of the follow-up period after perchlorate is given. In some of the cases studied discharge was not complete until 60 min after the perchlorate.
mesh_terms: D001665:Binding Sites / Q000187:drug effects; D002231:Carbimazole / Q000494:pharmacology; D006801:Humans; D006980:Hyperthyroidism / Q000175:diagnosis* / Q000188:drug therapy / Q000378:metabolism; D007455:Iodine / Q000378:metabolism*; D010472:Perchlorates; D017670:Sodium Compounds; D013961:Thyroid Gland / Q000378:metabolism*
chemical_list: D010472:Perchlorates; D017670:Sodium Compounds; D002231:Carbimazole; D007455:Iodine; C031068:sodium perchlorate