Regulation of pituitary function by pituitary hormones

荷尔蒙信使分子从特定的细胞释放到普通循环中，到达遥远的靶细胞。然而，这些分子也可以被释放以影响邻近细胞的功能，如旁分泌或自分泌系统。在牛蛙脑垂体中，PRL细胞经常与促性腺激素细胞接触。体外实验发现，催乳素可增强黄体生成素细胞对促性腺激素释放激素的反应。随着细胞密度的降低，对GnRH的反应性变得不明显。在培养液中加入PRL可增强对促分泌剂的反应性，而加入抗PRL抗血清可在一定程度上降低反应性。其次，实验研究了游离糖蛋白激素α亚基对…分泌颗粒的影响，发现在培养上清液中加入α亚基可以促进PRL的释放。另一方面，我们发现相当数量的细胞表现出PRL的分泌垂体分散培养后，催乳素和生长激素水平均升高。这表明PRL和/或GH的转录或翻译被阻断，直到细胞分散和培养。放线菌亚胺阻断了这种细胞的出现。这些结果表明，同时分泌PRL和GH的细胞在分散和培养后，在被转移到体外系统之前就拥有这些激素的mRNAs。此外，几个PRL免疫反应细胞具有GHmRNA，催乳素mRNA也在几个GH免疫反应细胞中表达。结论：(1)PRL直接作用于促性腺激素细胞，以旁分泌方式增强其对GnRH的反应性。(2)GH细胞中PRL mRNA的翻译和PRL细胞中GH mRNA的翻译均由细胞分散和/或培养所触发，提示存在旁分泌因子抑制GH细胞中PRL mRNA的翻译和PRL细胞中GHmRNA的翻译。(3)PRL细胞分泌的α-亚基作为自分泌和/或旁分泌因子促进PRL的释放。较少

Hormonal messenger molecules are released from specific cells into the general circulation to reach distant target cells. However, the molecules can also be released to influence the function of neighboring cells as paracrine or autocrine system.In the bullfrog pituitary, PRL cells frequently located in contact with gonadotropin cells. It was found that PRL enhances the responsiveness of LH cells to GnRH in vitro. The responsiveness to GnRH became less conspicuous as the cell density was reduced. Addition of PRL to the medium enhanced the responsiveness to the secretagogue, and addition of antiserum against PRL lowered the responsiveness to a certain extent. Secondly, experiments were performed to study the effect of free alpha-subunit of glycoprotein hormones existing in the secretory granules of PRL.It was found that addition of alpha-subunit into the culture medium enhanced the release of PRL.On the other hand, we have found that a considerable number of cells exhibited secretion of … More both PRL and GH when the pituitaries were dispersed and cultured. This suggested that either transcription or translation of PRL and/or GH had been blocked until the cells were dispersed and cultured. Cycloheximide blocked the appearance of such cells. These findings indicated that the cells secreting both PRL and GH after dispersal and culture possessed the mRNAs for these hormones before they were transferred to an in vitro system. In addition, several of the PRL-immunoreactive cells possesses GHmRNA.Prolactin mRNA was also expressed in several of the GH immunoreactive cells.In conclusion, paracrine and autocrine regulation of pituitary cell function in amphibians were elucidated : (1) PRL acts directly on gonadotrophs to enhance their responsiveness to GnRH in a paracrine fashion. (2) Both translation of PRL mRNA in GH cells and translation of GH mRNA in PRL cells are triggered by cell dispersion and/or culture, suggesting the presence of paracrine factors that inhibit the translation of PRLmRNA in GH cells and of GHmRNA in PRL cells. (3) Alpha-subunit secreted by PRL cells acts as an autocrine and/or paracrine factor to enhance the release of PRL. Less