Effect of L-dopa on plasma TSH levels in primary hypothyroidism.
Plasma TSH responses after an i.v. injection of 100 mg of L-dopa were evaluated by radioimmunoassay in 4 normal euthyroid subjects and in 8 patients with primary hypothyroidism. In agreement with previous results, no variations to plasma TSH  levels were observed in the euthyroid subjects. In contrast, in primary hypothyroidism L-dopa induced a biphasic response in plasma TSH. In fact, we observed a transitory increase witha maximum at 30 min (mean plus or minus SEM equals 54 plus or minus 18%) followed by a decrease reading a minimum level of plasma TSH basal values at 90 min (mean plus or minus SEM equals 15 plus or minus 6%). Thesefindings demonstrate that the plasma TSH response to L-dopa in primary hypothyroidism is time-dependent . Some speculation on the possible mechanism of this action is presented.
D000328:Adult; D000367:Age Factors; D000368:Aged; D002784:Cholesterol / Q000097:blood; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000188:drug therapy* / Q000503:physiopathology; D007455:Iodine / Q000378:metabolism; D007980:Levodopa / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D011863:Radioimmunoassay; D012737:Sex Factors; D013961:Thyroid Gland / Q000503:physiopathology; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D013997:Time Factors
D007980:Levodopa; D013972:Thyrotropin; D007455:Iodine; D002784:Cholesterol; D013974:Thyroxine