Decreasing pH of rat embryos and fluids estimated by transplacental distribution of DMO.

Utilizing the transplacental distribution of a weak acid, 5,5-dimethyloxazolidine-2,4-dione (DMO), we have measured the pH of cells within the rat embryo in vivo on days 11.5-14 of gestation. This is a period of rapid organogenesis in this species when the cells of many organ systems begin to change from a proliferative mode into a differentiated state. We found that intracellular pH of the day 11.5 rat embryo is 7.47 +/- 0.03 and decreases steadily to day 14 at which time it reaches 7.11 +/- 0.03. Because there is a concomitant fall in proliferative rate over this span of development, we suggest this correlation to be additional evidence of an association between proliferation and alkalinization of the cell interior. A number of other compartments including embryo plasma, amniotic fluid, exocoelomic fluid, and yolk sac have a decreasing concentration of DMO as development advances, indicative of a steadily declining pH. These changes could have developmental and pharmacokinetic implications.