Naito H, Takahashi M, Suzuki Y
Endocrinol Jpn. 1981 Apr;28(2):151-6. doi: 10.1507/endocrj1954.28.151.
Ovulation and pseudopregnancy (psp) can be induced by cervical stimulation in persistent estrous rats maintained in a constant lighting condition (LL-psp rats). Different from the pattern of prolactin (PRL) secretion in usual psp rats maintained in a daily light-dark cycle (LD-psp rats), PRL secretion in these rats during the psp period does not occur in the form of two daily surges. The object of this study was to investigate the role of the external LD cycle for the expression of PRL surges. A large amount of PRL was released in LL-psp rats immediately after cervical stimulation, which is in contrast to LD-psp rats whose first secretion of PRL after cervical stimulation is known to depend on the time of day rather than the time of stimulation. The effect of the change in the lighting condition on the pattern of PRL secretion was investigated in LD- and LL-psp rats. Two surges of PRL were induced in LL-psp rats on Day 5 (Day 0 = day of cervical stimulation), if they were moved from LL to LD on Day 0. Conversely, PRL surges diminished in LD-psp rats on Day 5 if they were moved from LD to LL on Day 0. When the change in lighting conditions was made on Day 5, different results were obtained: In LL-psp rats two daily surges were not established on Day 8 in spite of an application of LD condition from Day 5. In LD-psp rats the two surges were still observed on Day 8, though other time of occurrence was shifted. These results suggest that there is a critical period at and shortly after the time of cervical stimulation during which external LD cycle can work as an entraining agent for the expression of PRL surges. Once PRL secretion is coupled to the external LD cycle, the oscillation continues even in LL condition in a free-running manner. Exposure to LL condition during this critical period inhibits the establishment of two daily PRL surges throughout a psp period.
在持续光照条件下维持的持续发情大鼠（LL-psp大鼠）中，通过宫颈刺激可诱导排卵和假孕（psp）。与维持在日常明暗循环中的普通psp大鼠（LD-psp大鼠）的催乳素（PRL）分泌模式不同，这些大鼠在psp期间PRL的分泌并非以每日两次高峰的形式出现。本研究的目的是探讨外部明暗循环对PRL高峰表达的作用。宫颈刺激后，LL-psp大鼠立即释放大量PRL，这与LD-psp大鼠相反，已知LD-psp大鼠宫颈刺激后的首次PRL分泌取决于一天中的时间而非刺激时间。研究了光照条件变化对LD-和LL-psp大鼠PRL分泌模式的影响。如果LL-psp大鼠在第0天从LL转移到LD，在第5天（第0天=宫颈刺激日）可诱导出两次PRL高峰。相反，如果LD-psp大鼠在第0天从LD转移到LL，第5天PRL高峰会减少。当在第5天改变光照条件时，得到了不同的结果：尽管从第5天开始应用LD条件，但LL-psp大鼠在第8天未建立每日两次高峰。在LD-psp大鼠中，第8天仍观察到两次高峰，不过出现的时间有所变化。这些结果表明，在宫颈刺激时及刺激后不久存在一个关键时期，在此期间外部明暗循环可作为PRL高峰表达的同步因子。一旦PRL分泌与外部明暗循环耦合，即使在LL条件下，振荡也会以自由运行的方式持续。在这个关键时期暴露于LL条件会抑制整个psp期间每日两次PRL高峰的建立。
