Dymshitz J, Ben-Jonathan N
Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46223.
Endocrinology. 1991 Nov;129(5):2535-40. doi: 10.1210/endo-129-5-2535.
The synthesis and release of PRL are regulated by a variety of factors that originate in the hypothalamus, peripheral tissues, or posterior pituitary (PP). We recently reported that coculture of anterior pituitary (AP) and PP cells induced an increase in both PRL cell content and the responsiveness of lactotrophs to TRH. The aim of the present study was to determine whether the augmented response to TRH is due to increased lactotroph sensitivity to this particular secretagogue or to enhancement of the releasable pool of PRL. Cells obtained from anterior pituitaries of adult male rats were plated either alone or together with PP cells at the same total density. Cells cultures were maintained in serum-free medium for 4 days and then incubated for 20 min with the designated substances. Angiotensin-II and TRH evoked a significantly larger release of PRL in AP + PP cocultures than in AP cells cultured alone; the greatest difference between the culture types was observed at the highest concentrations of both secretagogues. The stimulation of PRL release by KCl, the calcium ionophore A23187, and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate was higher in the presence of PP cells than in cultures of AP cells alone, although the magnitude of this effect was lower than that seen with PRL secretagogues. The concomitant application of A23187 and 12-O-tetradecanoylphorbol-13-acetate resulted in an increased response in both types of culture and a greater relative effect of PP cells on the evoked PRL release. In contrast to other secretagogues, oxytocin (OT) elicited a smaller response in AP + PP cocultures than in AP cultures. OT was present in significant amounts in medium from cocultures, apparently after being released from the severed neuronal terminals. When AP cultures were pretreated for 4 days with comparable concentrations of OT, the acute OT-evoked PRL release was greatly diminished. These findings suggest that coculture with PP cells increases the releasable pool of PRL in lactotrophs. The stored PRL is accessible for release by secretagogues known to act via the Ca2+ second messenger system, involving both Ca2+/calmodulin and protein kinase-C pathways. The diminished response of cocultures to OT is probably due to desensitization of lactotrophs by the residual amounts of this peptide present in the disrupted nerve endings.
催乳素（PRL）的合成与释放受多种因素调控，这些因素源于下丘脑、外周组织或垂体后叶（PP）。我们最近报道，垂体前叶（AP）细胞与PP细胞共培养可导致PRL细胞含量增加以及催乳素细胞对促甲状腺激素释放激素（TRH）的反应性增强。本研究的目的是确定对TRH反应增强是由于催乳素细胞对这种特定促分泌素的敏感性增加，还是由于PRL可释放池的增强。从成年雄性大鼠垂体前叶获取的细胞，以相同的总密度单独接种或与PP细胞一起接种。细胞培养物在无血清培养基中维持4天，然后用指定物质孵育20分钟。血管紧张素II和TRH在AP + PP共培养物中引起的PRL释放明显大于单独培养的AP细胞；在两种促分泌素的最高浓度下，观察到培养类型之间的最大差异。在有PP细胞存在的情况下，氯化钾、钙离子载体A23187和佛波酯12 - O - 十四酰佛波醇 - 13 - 乙酸酯对PRL释放的刺激作用高于单独的AP细胞培养物，尽管这种效应的幅度低于PRL促分泌素所观察到的幅度。同时应用A23187和12 - O - 十四酰佛波醇 - 13 - 乙酸酯导致两种培养类型的反应均增加，并且PP细胞对诱发的PRL释放具有更大的相对作用。与其他促分泌素相反，催产素（OT）在AP + PP共培养物中引起的反应比在AP培养物中小。OT在共培养物的培养基中大量存在，显然是从切断的神经末梢释放出来的。当AP培养物用相当浓度的OT预处理4天时，急性OT诱发的PRL释放大大减少。这些发现表明，与PP细胞共培养可增加催乳素细胞中PRL的可释放池。储存的PRL可通过已知通过Ca2 +第二信使系统起作用的促分泌素释放，这涉及Ca2 + /钙调蛋白和蛋白激酶C途径。共培养物对OT反应减弱可能是由于破坏的神经末梢中存在的这种肽的残留量使催乳素细胞脱敏。
