Amico J A, Thomas A, Hollingshead D J
Department of Medicine, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA. jamico+@pitt.edu
Endocr Res. 1997 Aug;23(3):141-56. doi: 10.3109/07435809709031849.
The nonapeptide oxytocin (OT) is important for milk ejection during lactation, uterine contractility at parturition, and the onset of maternal behavior. Sequential exposure to estradiol (E2) and progesterone (P) followed by P withdrawal increases OT mRNA in the paraventricular nucleus (PVN), and to a lesser degree the supraoptic nucleus (SON), of the rat 48 hours after the P is removed. Although increases in PVN OT mRNA are not accompanied by changes in posterior pituitary OT peptide content, the PVN contains OT neurons that project to both the posterior pituitary (magnocellular group) and extra pituitary sites (parvocellular groups). Steroid-induced increases in OT mRNA occur in both the magnocellular and the parvocellular regions of the PVN. The latter are believed to contribute to CNS release of OT which may be important for certain behaviors including the onset of maternal behavior. The same steroid sequence that increases PVN OT mRNA also induces maternal behavior in virgin ovariectomized rats. Exposure of animals to E2 and P for 2 weeks resulted in the shortest latency to the onset of maternal behavior in ovariectomized rats, whereas exposure for 6 days was associated with a longer latency. In this study we questioned if the duration of E2 and P exposure prior to P withdrawal is an important regulator of PVN OT mRNA levels. We compared OT mRNA levels in the PVN of virgin ovariectomized rats administered no steroid or sequential E2 and P for 2 weeks versus 6 days. On day 1 animals received steroid-filled or empty capsules followed by P-filled or empty capsules on day 3. In one steroid-treated group, E2 and P were continued for 6 days and in the other group for 14 days prior to P removal. Animals were sacrificed 48 hours after P removal. Levels of OT mRNA were compared among 6 day and 2 week steroid-treated animals and sham-treated animals. The relative abundance of OT mRNA was significantly increased, P < 0.05, in animals receiving the 2-week, but not the 6-day, steroid treatment compared to sham-treated animals. Pituitary OT peptide content was not significantly different among the three groups. We conclude that the duration of steroid exposure may be an important regulator of the level of OT mRNA in the PVN of the rat.
九肽催产素（OT）对于哺乳期的乳汁排出、分娩时的子宫收缩以及母性行为的启动都很重要。在大鼠体内，依次给予雌二醇（E2）和孕酮（P），随后撤掉P，会在撤掉P 48小时后使室旁核（PVN）中的OT mRNA增加，视上核（SON）中的增加程度较小。虽然PVN中OT mRNA的增加并未伴随着垂体后叶OT肽含量的变化，但PVN中含有投射到垂体后叶（大细胞群）和垂体外部位（小细胞群）的OT神经元。类固醇诱导的OT mRNA增加发生在PVN的大细胞和小细胞区域。后者被认为有助于OT在中枢神经系统的释放，这对于包括母性行为启动在内的某些行为可能很重要。增加PVN中OT mRNA的相同类固醇序列也会在未交配的去卵巢大鼠中诱导母性行为。让动物接受E2和P处理2周，去卵巢大鼠出现母性行为的潜伏期最短，而处理6天则潜伏期较长。在本研究中，我们质疑在撤掉P之前给予E2和P的持续时间是否是PVN中OT mRNA水平的重要调节因素。我们比较了未交配的去卵巢大鼠在未给予类固醇或依次给予E2和P 2周与6天后PVN中OT mRNA的水平。在第1天，动物接受装有类固醇或空的胶囊，然后在第3天接受装有P或空的胶囊。在一个类固醇处理组中，在撤掉P之前，E2和P持续6天，在另一组中持续14天。在撤掉P 48小时后处死动物。比较了接受6天和2周类固醇处理的动物以及假处理动物中OT mRNA的水平。与假处理动物相比，接受2周而非6天类固醇处理的动物中OT mRNA的相对丰度显著增加，P < 0.05。三组之间垂体OT肽含量没有显著差异。我们得出结论，类固醇暴露的持续时间可能是大鼠PVN中OT mRNA水平的重要调节因素。
