Pyridostigmine and metoclopramide do not restore the TSH response to TRH inhibited by L-thyroxine treatment in children with goiter

To define the role of somatostatin and dopamine in TSH suppression induced by L-thyroxine, 16 children (12 F, 4 M) on suppressive doses of L-thyroxine (3-4 mug/kg/day) for endemic goiter were studied. Firstly a conventional T RH test was performed in all subjects, in order to evaluate TSH, PRL and GH (basal study). A week later a second TRH test was carried out; one hour be fore the test, however, group A (9 patients) was given 60 mg pyridostigmine bromide po (pyridostigmine study) and group B (7 patients)10 mg metoclopra mide po (metoclopramide study). In the basal study, TSH was suppressed in b oth groups and levels did not increase following TRH administration, while PRL increased significantly and GH levels remained stable. In the pyridosti gmine study, TSH levels did not increase following TRH administration, whil e PRL and GH levels were both significantly raised. In the metoclopramide s tudy, TSH and GH levels were not raised following TRH administration, while a significantly greater increase of PRL was observed. In conclusion, suppr essive doses of L-thyroxine inhibit the TSH response to TRH, while they do not seem to affect GH and PRL secretion. Somatostatin and/or dopamine do no t seem to play a significant role in the L-thyroxine-induced ISH suppressio n. (C) 2000, Editrice Kurtis.