INTRACELLULAR PH OF MONKEY EMBRYOS AT VARIOUS STAGES OF ORGANOGENESISESTIMATED BY DIMETHADIONE DISTRIBUTION

Previous experiments using the transplacental distribution of C-14-DMO (5,5-dimethyloxazolidine-2,4-dione or commonly known as dimethadione) have demonstrated that the pH of rat embryos and fluids progressively decreases during organogenesis. The aim of the present experiments wa s to similarly evaluate pH changes during organogenesis in the cynomol gus monkey, which is a model for human embryogenesis. Using DMO quanti tated by gas chromatography-mass spectrometry as opposed to the counti ng of radiolabelled compound, cynomolgus monkey embryos were determine d to undergo a similar decrease in embryonic pH(i) over an approximate ly comparable period of development (Days 24-36 of gestation). The rat io of DMO in chorionic fluid to DMO in maternal plasma in the cynomolg us monkey also displayed a decrease with advancing gestational age ind icative of a pH decrease. The DMO transplacental distribution was foun d to be significantly slower in the cynomolgus monkey than that in rod ents. The present investigation indicates that the magnitude of the re duction of pH in embryonic cells and in extra-embryonic fluids over a period of organogenesis in the cynomolgus monkey is similar to the red uction detected in rodent embryos and fluids over a comparable develop mental period, but the relative gradient between maternal blood pH and embryonic intracellular pH is different. The difference in the pH gra dient between the two species may lead to differential transplacental distribution of exogenous and endogenous substances.