Patiño Reynaldo, Bolamba Digbo, Thomas Peter, Kumakura Naoki
U.S. Geological Survey Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, TX 79409-2120, USA.
Gen Comp Endocrinol. 2005 Apr;141(2):126-34. doi: 10.1016/j.ygcen.2004.12.006. Epub 2005 Jan 21.
In vitro studies of ovarian follicle maturation and ovulation in teleost fishes typically are conducted within a narrow range (7.5-7.8) of constant external (medium) pH, although there is evidence that pH can influence ovulation. Therefore, this study with Atlantic croaker investigated the effects of external pH on hormonally regulated in vitro maturation and ovulation as well as changes in the pH of ovarian fluid during in vivo maturation and ovulation. For the in vitro experiments, follicles were first incubated with human chorionic gonadotropin (hCG) to induce maturational and ovulatory competencies, and then with maturation-inducing hormone (MIH) to induce completion of maturation and ovulation. At a constant external pH within the range of 7.0-8.2, the lower pH levels (7.0-7.3) generally inhibited or slowed down hormonally induced maturation and ovulation whereas higher pH (7.6-8.2) facilitated these processes. When ovarian follicles were incubated at a constant pH of 7.6 during the priming incubation with hCG, changing the external pH during the incubation with MIH had relatively little effect on oocyte maturation or ovulation. Thus, the inhibitory effect of constant low levels of external pH (7.0-7.3) on maturation and ovulation may be primarily due to disruptions in the gonadotropin-dependent acquisition of maturational and ovulatory competencies. The pH of ovarian fluid remained constant at 8.5 during in vivo ovarian follicle maturation and ovulation. Subsequent in vitro tests showed that external pH of 8.5 enhances hormonally induced maturation and ovulation relative to pH of 7.6. These observations suggest that attention should be paid to the pH of incubation media used in basic research and in biotechnological applications relying on in vitro maturation and ovulation in teleosts. Further, an understanding of the physiological significance of the enhancing effect of alkaline pH on maturation and ovulation will require determination of the intrafollicular pH around the oocyte during the periovulatory period.
硬骨鱼类卵巢卵泡成熟和排卵的体外研究通常在恒定的外部（培养基）pH值的狭窄范围内（7.5 - 7.8）进行，尽管有证据表明pH值会影响排卵。因此，本研究以大西洋鲱鱼为对象，研究了外部pH值对激素调节的体外成熟和排卵的影响，以及体内成熟和排卵过程中卵巢液pH值的变化。对于体外实验，卵泡首先与人绒毛膜促性腺激素（hCG）一起孵育以诱导成熟和排卵能力，然后与成熟诱导激素（MIH）一起孵育以诱导成熟和排卵的完成。在7.0 - 8.2范围内的恒定外部pH值下，较低的pH水平（7.0 - 7.3）通常会抑制或减缓激素诱导的成熟和排卵，而较高的pH值（7.6 - 8.2）则促进这些过程。当在与hCG的预孵育期间将卵巢卵泡在恒定pH值7.6下孵育时，在与MIH孵育期间改变外部pH值对卵母细胞成熟或排卵的影响相对较小。因此，恒定的低水平外部pH值（7.0 - 7.3）对成熟和排卵的抑制作用可能主要是由于促性腺激素依赖性成熟和排卵能力的获得受到破坏。在体内卵巢卵泡成熟和排卵过程中，卵巢液的pH值保持在8.5不变。随后的体外试验表明，相对于pH值7.6，外部pH值8.5增强了激素诱导的成熟和排卵。这些观察结果表明，在基础研究以及依赖硬骨鱼类体外成熟和排卵的生物技术应用中，应注意所用孵育培养基的pH值。此外，要理解碱性pH值对成熟和排卵的增强作用的生理意义，需要确定排卵期间卵母细胞周围卵泡内的pH值。
