A 46-year-old female motorcyclist, who suffered injuries to the brain stem in a 
traffic accident, showed hypotensive and bradycardiac responses to 
thyrotropin-releasing hormone (TRH) given to counter consciousness disturbance. 
The cardiodepressive responses to TRH were reduced with i.v. pretreatment with 
atropine sulfate, suggesting an involvement of the vagal nervous system in the 
development of the responses. Furthermore, this patient had complicated 
impairments in the sympathetic nervous system, which were revealed by the 
results of testing baroreceptor reflex sensitivity to pharmacological 
alterations in blood pressure. We thus speculate that the hypotensive and 
bradycardiac effects of TRH observed in this patient may result from 
derangements of the sympathetic nervous system caused by the injuries. This case 
report is believed to be a novel description of the cardiodepressive effects of 
TRH.