Antinociceptive activity of TRH metabolites in the mouse.

The antinociceptive action of the 2 main metabolites of thyrotropin-releasing hormone (TRH), pyroglutamyl-histidyl-proline (TRH-OH) and histidyl-proline-diketopiperazine or cyclo(His-Pro), were studied using mechanical (Haffner's test) and chemical (phenyl-p-benzoquinone writhing test) stimuli. TRH has previously been shown to be active against both these stimuli. TRH-OH showed an antinociceptive action against both stimuli, while cyclo(His-Pro) had a dose-dependent effect only against a mechanical stimulus.