Release of thyrotropin and prolactin by a thyrotropin-releasing hormone (TRH) precursor, TRH-Gly: conversion to TRH is sufficient for in vivo effects.
Release of thyrotropin and prolactin by a thyrotropin-releasing hormone (TRH) precursor, TRH-Gly: conversion to TRH is sufficient for in vivo effects.
复制标题
促甲状腺素释放激素 (TRH) 前体 TRH-Gly 释放促甲状腺素和催乳素：转化为 TRH 足以产生体内作用。
DOI：
10.1159/000125654
复制
发表时间：
1990
影响因子：
4.1
通讯作者：
Hershman,JM
中科院分区：
文献类型：
--
作者：
Pekary,AE;Stephens,R;Simard,M;Pang,XP;Smith,V;DiStefano3rd,JJ;Hershman,JM
TRH-Gly (pGlu-His-Pro-Gly) 是促甲状腺素释放激素 (TRH, pGlu-His-Pro-NH2) 的生物合成前体，刺激垂体促甲状腺素 (TSH) 和催乳素释放的机制已在乌拉坦麻醉的 2 个月大（250 g）雄性 Sprague-Dawley 大鼠中进行了研究，并在体外用GH3细胞，大鼠垂体前叶肿瘤细胞系。我们使用特定的放射免疫测定法来测量大鼠皮质、下丘脑、髓质、眼睛和全血中的TRH-Gly和TRH水平，作为处死前40分钟施用的TRH和TRH-Gly的脑池内(IC)剂量的函数。 IC 注射 1.0 mg TRH-Gly 导致下丘脑、髓质和血液中 TRH 水平显着增加 (p < 0.005)。通过放射免疫测定比较大鼠 TSH 的 IC 和心内 (IK) TRH 和 TRH-Gly 释放的相对效力，并使用基于 TRH-Gly α-酰胺化的体内动力学的估计进一步完善。还研究了 TRH-Gly 与 GH3 细胞上 TRH 质膜受体的结合。关于TSH释放，给予IC的TRH-Gly仅具有给予IC的TRH效力的0.042%，并且与其IC α-酰胺化速率一致。 IK TRH-Gly 的 TSH 释放效力是 IK TRH 的 0.16%，并且也与其血管内转化为 TRH 的速率一致。平均 TSH 响应峰值出现在 IC TRH-Gly 或 IC TRH 注射后 20 分钟，但 IC TRH-Gly 的峰值后下降较慢。血液TRH-Gly和TRH的最高水平分别出现在IC施用TRH-Gly和TRH后20分钟。 IC TRH-Gly 后直接测量的 TSH 释放相对效力与 IC TRH-Gly 转化为 TRH 的速率得出的一致性表明，IC TRH-Gly 在通过血脑屏障之前必须首先被脑脊液中的 α-酰胺化酶转化为 TRH。 TRH-Gly与GH3细胞TRH受体的交叉反应性是TRH的0.45%，而GH3细胞响应TRH-Gly释放催乳素的体外效力是TRH的0.41%。 GH3 细胞在有或没有 50 µg TRH-Gly/ml 的情况下孵育 3 小时，显示细胞外或细胞内 TRH 浓度没有显着增加。我们得出结论，TRH-Gly 转化为 TRH 是刺激大鼠 TSH 释放的最可能的解释，但体外 GH3 细胞响应 TRH-Gly 释放催乳素可能是通过 TRH-Gly 与 TRH 受体的交叉反应介导的。
The mechanism by which TRH-Gly (pGlu-His-Pro-Gly), a biosynthetic precursor of thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH2), stimulates pituitary thyrotropin (TSH) and prolactin release has been studied in urethane-anesthetized 2-month-old (250 g) male Sprague-Dawley rats and in vitro with GH3cells, a rat anterior pituitary tumor cell line. We used specific radioimmunoassays to measure TRH-Gly and TRH levels in rat cortex, hypothalamus, medulla, eyes and whole blood as a function of the intracisternal (IC) dose of TRH and TRH-Gly administered 40 min prior to sacrifice. IC injection of 1.0 mg of TRH-Gly led to a significant (p < 0.005) increase in the TRH levels in hypothalamus, medulla and blood. The relative potency of IC and intracardiac (IK) TRH and TRH-Gly release of rat TSH was compared by radioimmunoassay and further refined using estimates based on in vivo kinetics of TRH-Gly alpha-amidation. The binding of TRH-Gly to the plasma membrane receptors for TRH on GH3cells was also investigated. In regard to TSH release, TRH-Gly given IC had only 0.042% of the potency of TRH given IC and was consistent with its rate of IC alpha-amidation. IK TRH-Gly had 0.16% of the potency of IK TRH of TSH release and was also consistent with its rate of intravascular conversion to TRH. The mean peak TSH response occurred at 20 min after IC TRH-Gly or IC TRH injection but the post-peak decline was slower for IC TRH-Gly. The maximum levels of blood TRH-Gly and TRH both occurred at 20 min after IC administration of TRH-Gly and TRH, respectively. The agreement between the directly measured relative potency for TSH release following IC TRH-Gly and that derived from the rate of IC TRH-Gly conversion to TRH suggests that IC TRH-Gly must first be converted to TRH by alpha-amidating enzymes in the cerebrospinal fluid before it transits the blood-brain barrier. TRH-Gly cross-reactivity with the TRH receptor of GH3cells was 0.45% of that for TRH while the in vitro potency of prolactin release by GH3cells in response to TRH-Gly was 0.41% that for TRH. GH3cells incubated for 3 h with or without 50 µg TRH-Gly/ml revealed no significant increase in extracellular or intracellular TRH concentration. We conclude that conversion of TRH-Gly to TRH is the most likely explanation for the stimulation of TSH release in rats but in vitro release of prolactin from GH3cells in response to TRH-Gly administration may be mediated via TRH-Gly cross-reaction with the TRH receptor.