Stimulation of anterior pituitary galanin and prolactin gene expression in suckling rats

Recent evidence suggests that galanin, may regulate prolactin (PRL) secretion during lactation. In this article, we describe the regulation of anterior pituitary galanin and PRL gene expression during pregnancy and after parturition in the rat. Expression of galanin and PRL in the anterior pituitary were significantly higher at d 20 of pregnancy compared to diestrus. One day after parturition, galanin mRNA levels increased a further 4.5-fold. This post partum increase in gene expression was not observed for PRL. The increase in galanin gene expression was maintained above the diestrous level for at least 10 d after parturition. PRL mRNA expression, on the other hand, was largely unchanged after parturition. Although the increase in galanin gene expression 1 d after parturition was independent of suckling, subsequently, galanin, gene expression was significantly higher in nursing mothers. Anterior pituitary galanin gene expression was 12-fold higher in nursing mothers compared with those that were not, 3 d after parturition. Similarly, PRL gene expression was significantly lower in mothers who were not suckling their pups 3 d after parturition. Initiation of suckling alone was insufficient to stimulate galanin and PRL expression. Despite suckling for 2 d, removal of the suckling stimulus subsequently resulted in a rapid decrease in galanin gene expression. Hence, the stimulatory effect of suckling on galanin expression requires a sustained suckling stimulus. In conclusion, the data support the hypothesis that anterior pituitary galanin plays an important role during lactation, likely acting to amplify lactotroph stimulation through paracrine and autocrine mechanisms.     

Stimulation of anterior pituitary prolactin release by melittin, an activator of phospholipase A2

Melittin, a 26-amino acid polypeptide contained in bee venom and an activator of phospholipase A2, stimulated PRL secretion from bovine anterior pituitary cells in vitro. Over the dose range 0.25-2 micrograms/ml, melittin stimulation of PRL release was dose-related, reversible, and calcium dependent. Within this same dose range melittin did not deplete cell PRL stores, nor did it alter [3H]leucine uptake or trypan blue exclusion, indicators of cell viability. The phospholipase A2 inhibitors quinacrine and dibromoacetophenone blocked stimulation of PRL release by melittin and by themselves inhibited spontaneous PRL secretion. Addition of phospholipase A2 to pituitary cell cultures was associated with increased PRL secretion. A possible product of phospholipase A2 action, arachidonic acid, also stimulated PRL release. Indomethacin, an inhibitor of arachidonic acid conversion to prostaglandins, did not block melittin-induced PRL release but instead enhanced it. These data suggest that phospholipase A2 may participate in controlling PRL secretion by causing release of arachidonic acid from membrane phospholipids. Arachidonic acid or its noncyclooxygenase metabolite may serve as an intracellular regulator of secretion in the lactotroph.     

Cloning of a protein binding to the most proximal Pit-1 binding element of prolactin gene from human pituitary cDNA library

Activin is produced in mammalian ovarian follicles and is known to function as a paracrine as well as autocrine factor for folliculogenesis and oogenesis. We investigated the functional mechanism of activin using a hormone-supplemented serum-free culture system of granulosa cells isolated from diethylstilbestrol (DES)-primed 21-day-old rats. Recombinant human-activin A appeared to induce CycD2 and to act synergistically with FSH to promote G1/S transition and cell proliferation starting from 12 h after stimulation, accompanied by an increase of the hyperphosphorylated retinoblastoma protein (ppRb). Cells from unprimed rats gave similar results. FSH, in contrast, showed no CycD2-inducing activity, but turned out to modulate CycD2/cdk4 complex formation and enhance ppRb formation in conjunction with activin. These findings showed that the induction of CycD2 by activin and the synergistic effect of activin with FSH on ppRb formation play important roles in promoting G1/S transition in rat primary granulosa cells.     

Pit-1/GHF-1 and GH expression in the MCF-7 human breast adenocarcinoma cell line

GH expression in mammary tumors has been related to the increase and spreading of cell proliferation. Using the MCF-7 human breast adenocarcinoma cell line, it has been demonstrated that autocrine GH-stimulated mammary carcinoma cell proliferation decreased the apoptosis rate and enhanced cell spreading. Surprisingly, no data are available about the presence of Pit-1 (the main pituitary regulator of GH) or GH expression in this cell line. Using RT-PCR, Western blot and immunohistochemistry, we have demonstrated the presence of both mRNA coding Pit-1 and GH as well as Pit-1 and GH protein in the MCF-7 cell line. These data could imply that Pit-1 may be an adequate target to inhibit breast cell proliferation.     

促生长素释放激素及细胞因子对垂体促生长素基因表达的 …

目的 研究人促生长素释放激素（ｈＳＲＨ）、白细胞介素－１β（ＩＬ－１β）、白细胞介素－６（ＩＬ－６）和肿瘤坏死因子－ａ（ＴＮＦ－ａ）对垂体前叶促生长素细胞中生和素基表达的调控作用及其与Ｐｉｔ－１的关系。方法 将含有人促生长素基因启动子和萤光素酶报告基因的融合基历表达质粒（ｐＧＬ２－ＧＨ－Ｌｕｃ）单独转染或与人Ｐｉｔ－１基因表达质粒（ＰｃＤＮＡ－Ｐｉｔ－ｌｃＤＮＡ）共转染于大鼠ＧＨ３细胞中,体外观察