Developmental changes in the distribution of electrolytes within the horse conceptus during the second week of pregnancy

摘要

The equine conceptus expands particularly rapidly between Days 11 and 16 of pregnancy (Day 0, day of ovulation) when it is still highly mobile within the uterus [1]. Because the yolk-sac fluid is markedly hypotonic at least between Days 10 and 25 [2], it is unlikely that the fluid accumulation associated with this expansion involves the same type of ion concentration gradients that are responsible for earlier blastocyst expansion in mammals [3]. Enders et al. [4] have described subtrophoblastic compartments formed by the endoderm which completes the yolk sac on about Day 8, and have suggested that this "third compartment" may help draw water through the overlying epithelial cells. The present study, therefore, investigated electrolyte concentrations in various regions of the early conceptus and whether they change with developmental stage. To do so, conceptuses were rapidly frozen to minimize displacement of electrolytes and then processed for analysis by the technique of cryo-scanning electron microscopy (cryo-SEM) and energy dispersive X-ray (EDX) microanalysis [5].