[Intranasal TRH for the stimulation of hypophyseal and thyroid reserves. Preliminary report]

Intranasal, intravenous and oral TRH have been compared in 9 healthy volunteers. Intranasal administration of TRH leads to excellent stimulation of pituitary TSH secretion. Serum TSH levels are significantly higher than after intravenous TRH (p less than 0.005) and lower than after oral TRH (p less than 0.005). As with intravenous TRH, peak TSH response is reached at 20-30 minutes, but the stimulatory effect is prolonged and elevated TSH levels can be measured for up to 3 hours. Stimulation of T3 and free T4 at 3 hours is comparable in all three administration forms of TRH. The practical advantages of the intranasal route are that no intravenous injection is necessary, overnight fasting is not required and the duration of the test is short (30 minutes, in contrast to 3 hours in the oral test).