Thyrotropin-releasing hormone enhances motor neuron-evoked contractions of cultured human muscle.

Thyrotropin-releasing hormone (TRH), 1 to 2.7 mM, introduced to the medium of monolayer-cultured human muscle innervated by cocultured fetal rat spinal cord with dorsal root ganglia, increased muscle fiber contractions 4.9 times (p less than 0.005). Doses higher than 5 mM, after increasing contractions for a few seconds, caused complete inhibition of contraction (autorefractoriness). Neither aneurally cultured human muscle nor innervated cultured human muscle blocked by 1 mM d-tubocurarine was excited by TRH. Thus, in this system TRH appeared to excite muscle contractions through direct or indirect action on motor neurons.