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

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Abstract
Basal TSH [thyroid stimulating hormone] levels and the TSH response to TRH [thyrotropin releasing hormone] were evaluated in 26 males aged 20-48 yr with primary testicular failure, and 6 males aged 58-69 yr who were orchidectomized for prostatic carcinoma. The patients with testicular failure were sequentially challenged at 30 min intervals with i.v. LRH [luliberin] (100 .mu.g), TRH (200 .mu.g) 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 yr, who received the sequential protocol and 8 elderly controls aged 65-79 yr, who were given the LRH, TRH bolus. Mean .+-. SD basal TSH levels were 3.0 .+-. 1.2 .mu.U/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 .mu.U/ml in testicular failure and significantly greater than in the young controls, where it was 11.5 .+-. 5.0 .mu.U/ml. The peak levels in the castrates and in the elderly controls were similar to the young male controls. Total thyroxine and triiodothyronine and free thyroxine index were similar in all groups, although the subjects with 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.

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