El-Nefiawy Nagwa, Abdel-Hakim Khaled, Kanayama Naohiro
Department of Obstetrics and Gynecology, Hamamatsu University School of Medicine, 431-3192 Hamamatsu, Shizuoka, Japan.
Eur J Endocrinol. 2005 Feb;152(2):315-23. doi: 10.1530/eje.1.01837.
It is known that prostaglandin E2 (PGE2) plays a crucial role in the ovulation process. PGE2 mediates its actions through four subtypes of receptors designated EP1-EP4. However, the nature of the ovulation-promoting effect of PGE2 is not well understood. We have carried out this in vivo research utilizing a new selective EP4 receptor agonist (EP4A; APS-999 Na) to investigate its role in folliculogenesis aiming at more understanding of the biological mechanism of action of PGE2.
Immature, 22 day old Wistar rats were used. Animals were injected once either with placebo, 20 IU pregnant mare serum gonadotrophin (PMSG), or EP4A (10, 20 or 50 microg). In other experiments, EP4A was injected in PMSG stimulated rats. Ovarian follicle growth and development was assessed through total count and size measurement of ovulatory follicles in whole ovaries of the investigated groups. Utilizing immunohistochemistry, the spatial localization of the EP4 receptor in immature rat ovary and IL-8 pattern of expression after EP4A injection was also investigated.
Our study showed that injection of EP4A resulted in increased follicle growth and development compared with the control, in a time- and dose-dependent manner. The highest values for follicle count and size were observed 12 and 24 h after EP4A injection. EP4A induced follicle growth with morphological characteristics similar to that induced by the standard PMSG. Most dense immune staining for EP4 receptor was noticed in proliferating granulosa cells of the secondary follicles while those of the primordial and primary follicles were not stained. EP4A injection induced the expression of IL-8 in the follicles.
Our study revealed that: (i) the localization of EP4 receptor in the ovary implies a role in follicle growth, (ii) PGE2 induced ovarian follicle growth and development is mediated at least in part through the EP4 receptor, (iii) the action of EP4A is mediated through IL-8 up regulation and (iv) the new EP4A could be a promising reagent for various systems used to induce follicle maturation in clinical or agricultural fields. This knowledge may provide useful targets for manipulation of infertility.
已知前列腺素E2（PGE2）在排卵过程中起关键作用。PGE2通过四种名为EP1 - EP4的受体亚型介导其作用。然而，PGE2促排卵作用的本质尚未完全明确。我们进行了这项体内研究，使用一种新型选择性EP4受体激动剂（EP4A；APS - 999钠）来研究其在卵泡发生中的作用，旨在更深入了解PGE2的生物学作用机制。
使用22日龄未成熟的Wistar大鼠。动物分别注射一次安慰剂、20 IU孕马血清促性腺激素（PMSG）或EP4A（10、20或50微克）。在其他实验中，将EP4A注射到经PMSG刺激的大鼠体内。通过对研究组整个卵巢中排卵卵泡的总数和大小测量来评估卵巢卵泡的生长和发育。利用免疫组织化学方法，还研究了EP4受体在未成熟大鼠卵巢中的空间定位以及注射EP4A后白细胞介素 - 8的表达模式。
我们的研究表明，与对照组相比，注射EP4A可使卵泡生长和发育增加，且呈时间和剂量依赖性。在注射EP4A后12小时和24小时观察到卵泡计数和大小的最高值。EP4A诱导的卵泡生长具有与标准PMSG诱导的卵泡相似的形态特征。在次级卵泡的增殖颗粒细胞中观察到EP4受体的免疫染色最密集，而原始卵泡和初级卵泡的颗粒细胞未染色。注射EP4A可诱导卵泡中白细胞介素 - 8的表达。
我们的研究表明：（i）EP4受体在卵巢中的定位意味着其在卵泡生长中起作用；（ii）PGE2诱导的卵巢卵泡生长和发育至少部分通过EP4受体介导；（iii）EP4A的作用通过白细胞介素 - 8的上调介导；（iv）新型EP4A可能是临床或农业领域用于诱导卵泡成熟的各种系统中有前景的试剂。这一知识可能为治疗不孕症提供有用的靶点。
