Regulation of pituitary function by pituitary hormones

激素信使分子从特定细胞释放到全身循环中，到达远处的靶细胞。但是，这些分子也可以通过旁分泌或自分泌系统影响邻近细胞的功能。在牛蛙脑垂体中，PRL细胞经常与促性腺激素细胞接触。结果发现，PRL在体外可增强LH细胞对GnRH的反应性。随着细胞密度的降低，对GnRH的反应性变得不那么明显。加入催乳素可增强促分泌素的反应性，而加入抗催乳素血清可在一定程度上降低促分泌素的反应性。其次，实验研究了催乳素分泌颗粒中存在的糖蛋白激素游离α亚基的影响，发现培养基中添加α亚基可以促进催乳素的释放，另一方面，我们发现相当多的细胞表现出分泌催乳素的作用。 关于我们 分离培养垂体后叶后，PRL和GH均显著升高。这表明PRL和/或GH的转录或翻译被阻断，直到细胞被分散和培养。放线菌酮阻断了这种细胞的出现。这些发现表明，在分散和培养后分泌PRL和GH的细胞在转移到体外系统之前就具有这些激素的mRNA。结果表明：（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的翻译都是由细胞分散和/或培养引发的，这表明存在抑制GH细胞中PRL mRNA和PRL细胞中GHmRNA翻译的旁分泌因子。(3)由PRL细胞分泌的α-亚基作为自分泌和/或旁分泌因子来增强PRL的释放。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