Comparative study of intravenous, nasal, oral and buccal TRH administration among healthy subjects

Four different modes of TRH application (400 micrograms iv, 1 mg nasal, 10 mg buccal and 40 mg oral) were investigated in young healthy subjects for evaluation of thyrotropin (TSH) and prolactin (PRL) stimulation. Plasma TSH, PRL, T4, T3, thyroxine-binding-globulin (TBG) were measured by radioimmunoassay. There were significant increases of TSH and PRL following TRH stimulation by all test forms. Bolus injection of TRH led to maximal TSH and PRL plasma levels within 20 min to 30 min, compared with 30 min to 45 min following nasal administration. Buccal and oral application produced more prolonged TSH and PRL increases, achieving plateau levels after 120 min to 180 min. Stimulated PRL levels were higher in women than in men. Uniformity of PRL response was better after iv or nasal than buccal and oral TRH stimulation. Known side effects were lower after nasal than iv TRH application. Buccal and oral administration provoked no side effects. Nasal TRH application seems to be a well suited test form for TSH and PRL stimulation.