THYROTROPIN-RELEASING-HORMONE IMMUNOREACTIVITY IN RAT ADRENAL-TISSUE IS LOCALIZED IN MAST-CELLS

Pro-thyrotropin-releasing hormone (pro-TRH) has been shown to be prese nt throughout the central nervous system and in several peripheral tis sues. In adrenals, TRH immunoreactivity has been reported but not char acterized. We show here that two rat pro-TRH-derived peptides, TRH and prepro-TRH[160-169] (Ps4), were detected in extracts of rat adrenal g lands by enzyme immunoassay. Endogenous TRH and Ps4 were purified by g el exclusion chromatography and reverse-phase HPLC. Structural identif ication of each peptide was achieved by chromatographic comparison wit h synthetic standards. By using the indirect immunofluorescence techni que, TRH-immunoreactive cell bodies were found rather widely scattered outside the adrenal, in the brown adipose tissue in which the gland i s embedded. These immunofluorescent cells have the typical appearance of mast cells and are metachromatic after histological staining with a cidic Toluidine Blue. Our findings suggest that pro-TRH-derived peptid es exist in rat mast cells.