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。然而，这些分子也可以被释放来影响邻近细胞的功能，如旁分泌或自分泌系统。在牛蛙垂体中，PRL细胞经常与促性腺激素细胞接触。体外研究发现PRL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。培养基中添加PRL增强了对促泌素的反应性，添加抗PRL抗血清则在一定程度上降低了反应性。其次，我们通过实验研究了PRL分泌颗粒中存在的糖蛋白激素游离α亚基的作用。结果发现，在培养基中添加α亚基可以增强PRL的释放。另一方面，我们发现垂体分散培养时，相当数量的细胞同时分泌PRL和GH。这表明 PRL 和/或 GH 的转录或翻译已被阻断，直到细胞分散并培养。放线菌酮阻断了此类细胞的出现。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拥有这些激素的 mRNA。此外，一些PRL免疫反应性细胞具有GH mRNA。催乳素mRNA也在一些GH免疫反应性细胞中表达。 总之，阐明了两栖动物垂体细胞功能的旁分泌和自分泌调节：（1）PRL直接作用于促性腺激素，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/或培养触发的，表明存在抑制GH细胞中PRLmRNA和PRL细胞中GHmRNA翻译的旁分泌因子。 (3)PRL细胞分泌的α亚基作为自分泌和/或旁分泌因子，增强PRL的释放。较少的

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