Distribution of thyrotropin-releasing hormone (TRH) and precursor peptide (TRH-Gly) in adult rat tissues.
TRH (pGlu-His-Pro-NH2) arises from the post-translational processing of a larger precursor peptide containing multiple copies of the TRH progenitor sequence, Gln-His-Pro-Gly. Concentrations of TRH and its precursor peptide (TRH-Gly) were determined in serum and a variety of tissues of the rat using specific RIA systems. TRH and TRH-Gly immunoreactivities were detectable in almost all tissues studied. TRH was distributed mainly in neural tissues, with the highest mean concentration (126 pg/mg tissue) in hypothalamus. In extra-neural tissues, mean TRH levels ranged from 0.6-4.8 pg/mg tissue; the mean serum concentration was 12.4 pg/ml. In contrast to the distribution of TRH, relatively higher mean TRH-Gly concentrations were observed in serum (76.5 pg/ml) and in extraneural tissues, including prostate (83.3 pg/mg tissue), spleen (19.0 pg/mg), adrenal (16.2 pg/mg), kidney (13.3 pg/mg), and gastrointestinal tract (6.3-19.8 pg/mg). Among brain tissues, the TRH-Gly concentration was highest in pituitary gland (13.1 pg/mg). The mean ratio of TRH-Gly/TRH concentrations was less than 1 in neural tissues and pancreas. The lowest ratio (0.04) was observed in hypothalamus, and the highest ratio (66) in prostate gland. Assuming that tissue TRH-Gly levels reflect TRH synthesis, these results suggest that 1) the processing of TRH-Gly to TRH varies among tissues, 2) TRH-Gly to TRH conversion occurs most efficiently in neural tissues, and 3) TRH-Gly to TRH conversion may be a rate-limiting step in TRH biosynthesis.
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Department of Pediatrics, University of California-Los Angeles, School of Medicine, Harbor-UCLA Medical Center, Torrance 90509.
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Lam
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Fisher
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D000818:Animals; D002851:Chromatography, High Pressure Liquid; D009994:Osmolar Concentration; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013973:Thyrotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000378:metabolism*; D014018:Tissue Distribution
D013973:Thyrotropin-Releasing Hormone; C040476:thyrotropin-releasing hormone, Gly; D011761:Pyrrolidonecarboxylic Acid