Collins J L, Baltz J M
Loeb Research Institute and Human IVF Program, Ottawa Hospital, Ottawa, Ontario, Canada K1Y 4E9.
Biol Reprod. 1999 May;60(5):1188-93. doi: 10.1095/biolreprod60.5.1188.
Zygotes and early cleavage-stage embryos are very sensitive to increased osmolality in vitro, although the tonicity of their in vivo environment, oviductal fluid, is unknown. A preference for low osmolality in vitro might imply similar conditions in vivo or be specific to culture. Previous electron probe x-ray microanalysis measurements of total ion content predicted oviductal fluid osmolalities of 310-360 mOs/kg, higher than osmolalities tolerated by mouse zygotes in vitro. However, such indirect estimates may not reflect the tonicity experienced by embryos. We have now used embryos themselves as osmosensors to determine the tonicity of mouse oviductal fluid. In one method, we measured the mean volume of zygotes in undiluted oviductal fluid and compared this to the mean volumes measured for zygotes in media spanning a range of osmolalities. The osmolality corresponding to the measured mean volume in oviductal fluid was taken to be isotonic. In another, independent method, the sizes of zygotes and two-cell embryos were measured as a function of time beginning immediately after removal from oviducts. The osmolality in which the embryos neither swelled nor shrank was taken to be isotonic. Both methods yielded approximately the same range for the tonicity of oviductal fluid: around 290-300 mOs/kg.
合子和早期卵裂期胚胎在体外对渗透压升高非常敏感，尽管它们在体内环境（输卵管液）中的张力尚不清楚。体外对低渗透压的偏好可能意味着体内存在类似情况，或者是培养条件所特有的。先前通过电子探针X射线微分析对总离子含量的测量预测输卵管液的渗透压为310 - 360 mOs/kg，高于小鼠合子在体外所能耐受的渗透压。然而，这种间接估计可能无法反映胚胎所经历的张力。我们现在利用胚胎自身作为渗透压感受器来确定小鼠输卵管液的张力。在一种方法中，我们测量了未稀释的输卵管液中合子的平均体积，并将其与在一系列渗透压的培养基中测量的合子平均体积进行比较。与在输卵管液中测量的平均体积相对应的渗透压被视为等渗。在另一种独立方法中，从输卵管中取出合子和二细胞胚胎后，立即开始测量它们的大小随时间的变化。胚胎既不膨胀也不收缩时的渗透压被视为等渗。两种方法得出的输卵管液张力范围大致相同：约290 - 300 mOs/kg。
