Intranasal thyrotrophin releasing hormone is a potent stimulus for TSH release in man (comparison with intravenous and oral TRH).

Intranasally administered TRH was tested and compared to i.v. and oral TRH in respect to its efficacy of TSH stimulation and thereby the stimulation of thyroid reserve. TSH release after nasal application is as prompt as after the i.v. route, reaching a peak at 20 to 30 min. After that, however, compared to the i.v. administration its stimulatory effect is prolonged, lasting over 3 h. At the dose used in this study the peak TSH response after intranasal TRH administration was 14.7 +/- 1.6 mU/l compared to 8.4 +/- 1.4 and 23.1 +/- 4.4 mU/l after i.v. and oral administration respectively (P less than 0.005). Intranasal application of TRH is as potent as i.v. or oral TRH for the stimulation of thyroid reserve. At 3 h a marked increase of T3 and a smaller elevation of FT4 is observed (delta T3 = 48.4%, delta FT4 = 31.6%). The nasal peptide was well tolerated locally and systemic side effects were comparable to those of i.v. TRH. This form of application offers a practical advantage by avoiding intravenous injections. Its diagnostic potential in investigation of thyroid disease and its possible therapeutic application have yet to be elucidated.