Thyroid-stimulating hormone (tsh), triiodothyronine (t3) and thyroxine (t4) response to intravenous and oral stimulation with synthetic thyrotropin-releasing hormone (trh) in young healthy adults.

TSH, T3 and T4 response to stimulation with thyrotropin releasing hormone (TRH) has been investigated in 24 young healthy adults after intravenous injection and in 25 young healthy adults upon oral application of 40 mg of TRH. After intravenous injection the TSH concentration raises from a mean of 1.6 to a mean maximum of 11.7 muU/ml. A statistically significant sex difference could not be found. T3 shows a statistically significant increase which is however too small to be of diagnostic value in an individual test. After oral stimulation with 40 mg of TRH, TSH rises to a slightly higher maximum of 13.2 muU/ml after 3 h. The T3 increase from 1.5 to 2.19 ng/ml is significant and considerably higher than after intravenous stimulation. The thyroxin increase is statistically significant. The present results compare well with previously published data for intravenous stimulation. The oral route of TRH application has not yet been widely used and the present series establishes the normal response in young healthy adults. Repetitive stimulation with three times 40 mg of TRH leads to a decrease in TSH stimulation which reaches 5.8 muU/ml 3 h after the third dose. This is in contrast to a comparable increase in plasma T3.