The TSH response to TRH is exaggerated in primary testicular failure and normal in the male castrate.

Basal TSH levels and the TSH response to TRH have been evaluated in 26 males aged 20-48 years with primary testicular failure, and 6 males aged 58-69 years who had been orchidectomised for prostatic carcinoma. The patients with testicular failure were sequentially challenged at 30 min intervals with iv LRH (100 microgram), TRH (200 microgram) and the dopaminergic antagonist, metoclopramide (10 mg). The castrates received a bolus of LRH and TRH given together. The responses in the 2 patient groups were compared to a group of 28 healthy male controls aged 20-40 years, who received the sequential protocol and 8 elderly controls aged 65-79 years, who were given the LRH, TRH bolus. Mean +/- SD basal TSH levels were 3.0 +/- 1.2 muU/ml in primary testicular failure and significantly greater than both control and castrate groups. The peak TSH response to TRH was 18.4 +/- 7.4 muU/ml in testicular failure and significantly greater than in the young controls, where it was 11.5 +/- 5.0 muU/ml. The peak levels in the castrates and in the elderly controls were similar to the young male controls. Total T4 and T3, as well as FTI, primary testicular failure had a reduction in their T3 resin uptake. The normal TSH profile in the castrates indicates that a testicular factor produces the exaggerated responses in primary testicular failure.