A cryptic peptide (160-169) of thyrotropin-releasing hormone prohormone demonstrates biological activity in vivo and in vitro.
TRH is synthesized as a precursor peptide containing five copies of the sequence Gln-His-Pro-Gly, QHPG, flanked by paired basic amino acids, and linked by other peptides. We tested one cryptic peptide, PPT (160-169, SFPWMESDVT), as a possible physiological regulator of pituitary activity in vivo. Male rats were cannulated (jugular) and received a single dose of either PPT or TRH (10(-8)-10(-6) M). PPT caused no consistent effects on either TSH or PRL secretion, while TRH stimulated the secretion of both hormones. However, PPT stimulated a dose-dependent increase in both pituitary TSH beta and PRL mRNA content at 240 min similar to TRH. In primary cultures of rat pituitaries, PPT stimulated a maximum 4-fold increase in TSH beta mRNA and a 2-fold increase in PRL mRNA in 4 h, while TRH increased both TSH beta and PRL mRNA approximately 3-fold. Again, PPT had no significant effect on TSH or PRL secretion into the medium. Thus, PPT appears to be a physiological regulator of both TSH and PRL synthesis, but, unlike TRH, does not act as a secretagogue.
Carr
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Department of Clinical Investigation, Walter Reed Army Medical Center, Washington, D.C. 20307.
Fein
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Fisher
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Wessendorf
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Smallridge
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D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D008297:Male; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D011388:Prolactin / Q000235:genetics / Q000378:metabolism; D011498:Protein Precursors / Q000737:chemistry / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013972:Thyrotropin / Q000235:genetics / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000737:chemistry / Q000494:pharmacology*
D010446:Peptide Fragments; D011498:Protein Precursors; D012333:RNA, Messenger; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D013972:Thyrotropin