Simard M, Pekary A E, Smith V P, Hershman J M
Endocrinology Research Laboratory, Veterans Administration Wadsworth Medical Center, Los Angeles, CA 90073.
Peptides. 1989 Jan-Feb;10(1):145-55. doi: 10.1016/0196-9781(89)90091-0.
In the present study we have examined the in vivo effects of thyroid hormones and TRH on tissue and blood levels of TRH and TRH-Gly (pGlu-His-Pro-Gly), a TRH precursor. Using specific radioimmunoassays (RIAs), we measured TRH immunoreactivity (TRH-IR) and TRH-Gly-IR concentrations in blood, hypothalamus, anterior and posterior pituitary, and thyroid in euthyroid, hypothyroid and thyroxine (T4)-treated 250 g male Sprague-Dawley rats. TRH-Gly-IR and TRH-IR were detected in all of these tissues. Highly significant positive correlations between whole blood TRH-Gly-IR levels and the corresponding serum TSH values (p less than 0.01), whole blood TRH-IR versus serum TSH (p less than 0.01) and whole blood TRH-Gly-IR versus whole blood TRH-IR (p less than 0.01) are consistent with cosecretion of TRH and TRH precursor peptides into the circulation. Euthyroid rats injected with TRH IP (1 microgram/100 g b.wt.) and hypothyroid rats had 4-fold higher whole blood TRH-Gly-IR levels compared to euthyroid controls (p less than 0.0005). Injection of TRH into euthyroid rats significantly increased the TRH-Gly-IR concentration in the hypothalamus, anterior and posterior pituitary and thyroid. The increase in blood TRH-Gly-IR following intravenous TRH may be due, in part, to partial saturation of TRH-degrading enzymes in blood and cell membranes. The ratio of TRH-Gly to TRH was significantly increased in the anterior pituitary by hypothyroidism and TRH injection, suggesting that thyroid hormones and TRH regulate the alpha-amidation of TRH-Gly to form TRH in this tissue. TRH-Gly levels of pooled pituitary and thyroid extracts quantitated by a combination of TRH-Gly RIA and high performance liquid chromatography (HPLC) revealed several-fold increases following incubation at 60 degrees C. Heating at this temperature may block the alpha-amidation activity in extra-hypothalamic tissues but not the "trypsin-like" enzymes which cleave prepro-TRH into TRH-Gly-immunoreactive peptides.
在本研究中，我们检测了甲状腺激素和促甲状腺激素释放激素（TRH）对TRH及TRH前体TRH-甘氨酸（pGlu-His-Pro-Gly）的组织和血液水平的体内效应。使用特异性放射免疫分析法（RIA），我们测定了正常甲状腺、甲状腺功能减退和经甲状腺素（T4）处理的250 g雄性Sprague-Dawley大鼠血液、下丘脑、垂体前叶和后叶以及甲状腺中的TRH免疫反应性（TRH-IR）和TRH-甘氨酸免疫反应性（TRH-Gly-IR）浓度。在所有这些组织中均检测到了TRH-Gly-IR和TRH-IR。全血TRH-Gly-IR水平与相应血清促甲状腺激素（TSH）值之间（p<0.01）、全血TRH-IR与血清TSH之间（p<0.01）以及全血TRH-Gly-IR与全血TRH-IR之间（p<0.01）高度显著的正相关，与TRH和TRH前体肽共同分泌入循环系统一致。腹腔注射TRH（1微克/100克体重）的正常甲状腺大鼠和甲状腺功能减退大鼠的全血TRH-Gly-IR水平比正常甲状腺对照大鼠高4倍（p<0.0005）。向正常甲状腺大鼠注射TRH可显著增加下丘脑、垂体前叶和后叶以及甲状腺中的TRH-Gly-IR浓度。静脉注射TRH后血液中TRH-Gly-IR的增加可能部分归因于血液和细胞膜中TRH降解酶的部分饱和。甲状腺功能减退和注射TRH可使垂体前叶中TRH-甘氨酸与TRH的比例显著增加，表明甲状腺激素和TRH调节该组织中TRH-甘氨酸的α-酰胺化以形成TRH。通过TRH-甘氨酸RIA和高效液相色谱法（HPLC）联合定量的垂体和甲状腺提取物混合液中的TRH-甘氨酸水平在60℃孵育后显示增加了几倍。在此温度下加热可能会阻断下丘脑外组织中的α-酰胺化活性，但不会阻断将前促甲状腺激素释放激素切割成TRH-甘氨酸免疫反应性肽的“胰蛋白酶样”酶。
