The direct influence of Thyrotropin-Releasing Hormone (TRH) on the smooth muscle of rat duodenum

Thyrotropin-releasing hormone added in vitro induced a distinct, dose dependent relaxant response in the isolated duodenum of the rat. Such a distinct response to TRH was not produced in the isolated jejenum, ileum or colon. The duodenal response was not blocked by tetrodotoxin, phenoxybenzamine or propranolol. Thus the direct influence of TRH on the smooth muscle was demonstrated.