In vivo and in vitro effects of dexamethasone on pituitary thyrotrophin-releasing hormone-like peptide concentrations in the rat.
The novel peptide, pyroglutamyl-glutamyl-proline amide (pGlu-Glu-ProNH2; EEP), which has structural and immunological similarities to TRH (pGlu-His-ProNH2) has recently been shown to contribute to total TRH-like immunoreactivity (t-TRH-LI) detected in the rabbit prostate and rat and porcine anterior pituitary. In this study, the effects of dexamethasone (DEX) on rat pituitary TRH-like peptide levels in the rat were determined. TRH-like immunoreactivity (TRH-LI) was separated by ion exchange chromatography and detected by TRH RIA. Anion exchange chromatographic analysis suggested that EEP-like immunoreactivity (EEP-LI) accounted for 15.0 +/- 1.2 pmol t-TRH-LI/g (70.4 +/- 3.9%) in the control anterior pituitary with the remaining t-TRH-LI being due to TRH-LI. Following DEX treatment pituitary EEP-LI and TRH-LI increased by 200% and 400% (P < 0.001) respectively, constituting a 2.5-fold increase in t-TRH-LI in the pituitary. TRH-LI now accounted for 45.7 +/- 5.3% of t-TRH-LI compared with 29.6 +/- 4.1% in the controls. TRH-LI, but not EEP-LI, was detected in the hypothalamus and posterior pituitary, suggesting that EEP-LI is synthesised within the anterior pituitary. DEX also caused a 2.6-fold rise (P < 0.001) in t-TRH-LI in dispersed, cultured anterior pituitary cells. Chromatographic analysis of cultured pituitary cell extracts revealed that the majority of t-TRH-LI (> 98%) was due to TRH-LI.(ABSTRACT TRUNCATED AT 250 WORDS)
Akinsanya
K O
KO
Department of Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, London, UK.
Jamal
H
H
Ghatei
M A
MA
Bloom
S R
SR
D000818:Animals; D002478:Cells, Cultured; D002852:Chromatography, Ion Exchange; D003907:Dexamethasone / Q000494:pharmacology*; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000737:chemistry; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D013973:Thyrotropin-Releasing Hormone / Q000032:analysis / Q000378:metabolism*
D013973:Thyrotropin-Releasing Hormone; D003907:Dexamethasone