Phelps S J, Moy J A, Lawson D M
Department of Physiology, Wayne State University School of Medicine, Detroit, MI 48201.
Life Sci. 1991;49(26):1965-72. doi: 10.1016/0024-3205(91)90638-r.
Previous reports have shown that pituitary prolactin is rapidly transformed to a less soluble, but much more releasable, form prior to release from the lactotroph. One manifestation of this transformation is that pituitary prolactin depletion is significantly greater than concurrent release both in vivo and in vitro. The objective of this study was to compare the magnitude and temporal dynamics of depletion and release from pituitaries of ovariectomized estrogen-treated rats of three different strains in vitro to assess the effect of strain on the transformation process. Mature ovariectomized Wistar-Furth (WF), Sprague-Dawley (SD) and Long-Evans (LE) rats (7-10/group) were killed by decapitation 7 days after a single s.c. injection of 100 micrograms of polyestradiol phosphate. The anterior pituitaries were quickly removed and cut into quarters which were incubated for up to 4 hrs in the absence of dopamine or other prolactin secretagogues. Representative fragments from each strain were not incubated but were snap frozen to measure pre-incubation content. Fragments from each strain were removed from incubation at 30, 60, 120, 180 and 240 min for prolactin content measurement. Medium was collected at 30 min intervals and replaced with fresh medium. The experiments were repeated twice. Prolactin in medium and pituitary homogenates was measured by radioimmunoassays using NIAMDD-RP-1 as standard. In all three stains release of prolactin was approximately 30-50% of the prolactin depleted from the pituitary in 4 hrs. Strains varied in the magnitude of this difference and the time course over which it occurred. WF and SD rats showed significantly greater depletion and release of prolactin than did LE rats when the data were expressed as micrograms prolactin/mg pituitary. When the data were expressed as a percentage of prolactin available for release, the differences in depletion between strains disappeared and the LE rats released a significantly greater percentage of the prolactin available for release than did the other two strains. We conclude that pituitary prolactin undergoes a process of transformation prior to release which causes it to disappear from the pituitary but not appear in culture medium. We further conclude that the magnitude and temporal dynamics of this process are not equivalent across all strains of rats.
先前的报道表明，垂体催乳素在从催乳细胞释放之前会迅速转变为一种溶解性较低但更易释放的形式。这种转变的一个表现是，无论是在体内还是体外，垂体催乳素的耗竭都明显大于同时期的释放量。本研究的目的是比较体外培养的三种不同品系去卵巢并经雌激素处理的大鼠垂体中催乳素耗竭和释放的程度及时间动态变化，以评估品系对这种转变过程的影响。成熟的去卵巢Wistar-Furth（WF）、Sprague-Dawley（SD）和Long-Evans（LE）大鼠（每组7 - 10只）在单次皮下注射100微克磷酸聚雌二醇7天后断头处死。迅速取出垂体并切成四等份，在无多巴胺或其他催乳素促分泌剂的情况下孵育长达4小时。每个品系的代表性片段不进行孵育，而是速冻以测量孵育前的含量。在孵育30、60、120、180和240分钟时，从每个品系中取出片段测量催乳素含量。每隔30分钟收集培养基，并用新鲜培养基替换。实验重复两次。使用NIAMDD-RP-1作为标准品，通过放射免疫测定法测量培养基和垂体匀浆中的催乳素。在所有三个品系中，4小时内催乳素的释放量约为垂体中催乳素耗竭量的30% - 50%。不同品系在这种差异的程度以及发生的时间过程方面存在差异。当数据以微克催乳素/毫克垂体表示时，WF和SD大鼠的催乳素耗竭和释放量显著高于LE大鼠。当数据以可释放催乳素的百分比表示时，品系间耗竭的差异消失，并且LE大鼠释放的可释放催乳素的百分比显著高于其他两个品系。我们得出结论，垂体催乳素在释放前会经历一个转变过程，该过程使其从垂体中消失但未出现在培养基中。我们进一步得出结论，该过程的程度和时间动态在所有大鼠品系中并不相同。
