Lactic dehydrogenase of fetal ear fluids under ambient and high-intensity sound.

Lactic dehydrogenase (LDH) was determined in the fluids of the inner ear scalae and the middle ear cavity of fetal guinea pigs near term. Scalar dissimilarities in prenatal perilymph and distinctions between fetal and maternal perilymph suggest functional differentiation between the antenatal scalae vestibuli and tympani, elevated glycolytic activity in the prenatal vestibular channel and primarily aerobic processes in fetal perilymph although anaerobic metabolism is also evident. Disparities between fetal middle ear fluid and prenatal perilymph as well as maternal serum indicate that the former medium is probably not directly derived from either of the latter sources. After experimental treatment consisting of the presentation of high-intensity sound to gravid animals, the total LDH activity of the fetal middle ear fluid decreased.