TRH immunoreactivity in the thyroid gland

Methanol extracts of dog and pig thyroid tissue contained considerable amounts of thyrotropin releasing hormone immunoreactivity (iTRH): 2.98 +/- 1.38 and 1.83 +/- 0.58 pmol/g thyroid wet weight, respectively (mean +/- SD). This iTRH was not due to ether extractable materials and behaved like TRH standard in dilution experiments, during gel filtration on Sephadex G-25 and during thin layer chromatography on a silica gel plate. Cation exchange chromatography on SP-Sephadex C-25 revealed that the iTRH in methanol extract was heterogeneous. However, part of the iTRH applied on the column was eluted as synthetic TRH: 0.209 +/- 0.046 and 0.052 +/- 0.021 pmol/g dog and pig thyroid, respectively. During incubation with rat serum, the SP-Sephadex purified iTRH disappeared in parallel with TRH. These studies indicate that the thyroid contains small amounts of iTRH which behaves identically to synthetic TRH.