TRH-like immunoreactivity in urine, serum and extrahypothalamic brain: non-identity with synthetic pyroglu-hist-pro-NH2 (TRH).

TRH-like immunoreactive substances obtained from several areas of rat brain and from human serum and urine were chromatographically separated by TLC and the resulting immunoreactive 'elution profiles' compared with that obtained for pyroglu-hist-pro-NH2 (TRH). For hypothalamus and septal-preoptic samples TRH was present, but represented less than 100% of the immunoreactive substances. For cortex, amygdala, brain stem, serum and urine, no TRH was detectable in the immunoreactive substances from those samples. The implications of these findings in relation to 'TRH' distribution studies and validation of small peptide RIAs are discussed.