Light-and-Dark Signal for the Initiation of Prolactin Surges in Cervically Stimulated Rats

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概要

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• 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.<BR>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 LLpsp rats on Day 5 (Day 0=day of cervical stimulation), if they were moved from LL to LD on Day O. Conversely, PRL surges diminished in LD-psp rats on Day 5 if they were moved from LD to LL on Day O. 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 the time of occurrence was shifted.<BR>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.

• 社団法人 日本内分泌学会の論文

著者

• TAKAHASHI MICHIO

  Laboratory of Veterinary Physiology, Faculty of Agriculture, University of Tokyo

• SUZUKI YOSHISUKE

  Laboratory of Veterinary Physiology, Faculty of Agriculture, University of Tokyo

• NAITO HIROYUKI

  Laboratory of Veterinary Physiology, Faculty of Agriculture, University of Tokyo

• TAKAHASHI Michio

  Laboratories of Veterinary Physiology

関連論文

• Changes in Concentration of Hypothalamic Cytosolic Progestin Receptors at the Initiation of Pseudopregnancy in Rats
• Preovulatory Changes in Luteinizing Hormone Releasing Hormone Concentrations in Peripheral Plasma in Constant Estrous Rats at Induced Ovulation
• Light-and-Dark Signal for the Initiation of Prolactin Surges in Cervically Stimulated Rats
• Ovulation in Light-Estrous Rats Induced by Darkness
• Changes in 20.ALPHA.-Hydroxysteroid Dehydrogenase mRNA in the Ovary of Immature Rats Bearing a Single Generation of Corpora Lutea.

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