Analysis of the developmental process of immature growth hormone cells in the rat fetus.

本研究成功地在体外复制了糖皮质激素诱导生长激素（GH），并利用该体外系统分析了胎儿垂体诱导GH的分子机制。E18胎垂体腺在体外无血清mem - α中孵育，添加或不添加DEX （50nM）。孵育24h后，仅在DEX孵育的E19胎组织中，GHmRNA的积累达到与对照组相适应的水平。这表明DEX作用的主要部位是垂体，母体因素、胎盘或胎儿下丘脑的影响并不是胎儿垂体中生长激素产生的先决条件。当E17垂体与DEX孵育时，GHmRNA积累水平明显降低。这被认为是能够对DEX产生反应的细胞数量差异的结果。在孵育5或10小时后，DEX对GHmRNA的诱导不明显，然而，如果在孵育24小时的前10小时培养基中存在DEX，则在孵育的其余时间中不需要DEX的持续存在来诱导GH。添加环己亚胺，或嘌呤霉素，蛋白质合成抑制剂，完全抑制生长激素诱导的DEX。综上所述，DEX对胎儿垂体GHmRNA的诱导是由垂体响应DEX而产生的未知因子介导的，可能激活了GH基因的转录。

In the present study, growth hormone (GH) induction by glucocorticoid was successfully reproduced in vitro, and using this in vitro system, the molecular mechanisms underlying the GH-induction in the fetal pituitary gland was analyzed.The pituitary glands of E18 fetuses were incubated in vitro in serum free MEM-alpha with or without an addition of DEX (50nM). After 24h incubation, GHmRNA was accumulated only in the tissue incubated with DEX to a compatible level to that of control E19 fetuses. This ihdicates that the primary site of the DEX action is the pituitary gland and the influences of maternal factors, placenta or fetal hypothalamus are not prerequisite with respect to the initiation of GH production in the fetal pituitary gland. When E17 pituitaries were incubated with DEX,a distinct reduction of the level of GHmRNA accumulation was noted. This is considered to be the consequence of the difference in the number of tha cells which are capable of responding DEX.DEX induction of GHmRNA was not evident after 5 or 10 h incubation, however, if DEX was present in the medium for first 10h of the 24h-incubation, the continuous presence of DEX was not required for GH induction for the rest of incubation period. An addition of the cycloheximide, or puromycin, inhibitors of protein synthesis, completely inhibited the GH induction by DEX.These results taken as a whole suggest that the induction of GHmRNA in the fetal pituitary gland by DEX is mediated by unknown factor which is produced in pituitary gland in response to DEX,and probably activates the GH gene transcription.