Absorption of compounds in medium by the oil covering microdrop cultures

Microdrops of medium under either paraffin or silicone oil are commonly used for culture of early mammalian embryos. Radiolabeled estradiol, progesterone, and androstenedione in drops of medium under oil decreased by 51, 89, and 77%, respectively, after 24-hr incubation. Up to 14% of labeled estradiol moved to another drop of medium by passing through the oil. Several other substances tested (FSH, leucine, glucose, lactate, sodium ion, PGE2, PGF2 alpha) did not pass into the oil. Both paraffin and silicone oils can alter the composition of culture medium by absorbing and transferring certain types of compounds.