It is well established that the suckling stimulus sensitizes or primes the anterior pituitary to PRL-releasing stimuli. It is also recognized that PRL-secreting cells from a given animal are not all alike but instead exhibit a considerable degree of functional heterogeneity. The goal of the present study was to determine whether the suckling-induced priming phenomenon is manifest at the cellular level by shifts in the relative abundance of various mammotrope subpopulations. This was accomplished by using reverse hemolytic plaque assays to evaluate the secretory characteristics of individual PRL secretors derived from lactating rats either before or after the transient application of a suckling stimulus. Groups of day 10 lactating rats separated from their litters for 4 h were either killed immediately or were reunited briefly (10 min) with their pups before death. Adenohypophyseal cells obtained after trypsin dispersion were then subjected to plaque assays for PRL. Mammotropes derived from suckled rats were, on average, considerably more responsive to the stimulatory actions of TRH and angiotensin II and less susceptible to inhibition by dopamine. Mammotropes from nonsuckled rats exhibited a bimodal frequency distribution in which plaques from the second mode were roughly 6-8 times larger (released considerably more PRL) than those from the first. Superimposition of suckling (or in vitro treatment with dopamine) caused the second mode to disappear. Suckling also enhanced greatly the fraction of PRL cells that shifted from the first to the second mode (i.e. released more hormone) after treatment with TRH or angiotensin II. Taken together, our results demonstrate that the suckling-induced sensitization of pituitary tissue to PRL-releasing stimuli is manifest at the cellular level as proportional shifts toward those cells most responsive to stimulatory secretagogues and away from those most susceptible to inhibition by dopamine.

译文

众所周知,哺乳刺激使垂体前叶对PRL释放刺激敏感或引发。还认识到,来自给定动物的PRL分泌细胞并非全部相同,而是表现出相当程度的功能异质性。本研究的目的是确定哺乳诱导的引发现象是否在细胞水平上表现为各种猛犸象亚群相对丰度的变化。这是通过使用反向溶血斑块测定法来评估在短暂施加乳汁刺激之前或之后源自泌乳大鼠的单个PRL分泌物的分泌特性来实现的。与幼仔分开4小时的第10天哺乳期大鼠组被立即杀死或在死亡前与幼崽短暂团聚 (10分钟)。然后对胰蛋白酶分散后获得的腺垂体细胞进行PRL的斑块分析。平均而言,来自乳鼠的猛犸象对TRH和血管紧张素II的刺激作用的反应要高得多,并且不易受到多巴胺的抑制。来自未哺乳大鼠的猛犸象表现出双峰频率分布,其中第二种模式的斑块比第一种模式的斑块大约6-8倍 (释放的PRL明显更多)。乳汁的叠加 (或用多巴胺进行体外治疗) 导致第二种模式消失。在用TRH或血管紧张素II治疗后,哺乳还大大增强了从第一种模式转变为第二种模式 (即释放更多激素) 的PRL细胞的比例。综合而言,我们的结果表明,哺乳诱导的垂体组织对PRL释放刺激的敏感性在细胞水平上表现为向对刺激性促分泌剂最有反应的细胞成比例地转移,而远离那些最易受多巴胺抑制的细胞。

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