Enzymatic activity of inner and middle ear fluids in fetal guinea pigs under ambient and high-intensity sound presentation.

The enzymes in perilymph of the inner ear scala and within fluid filling the middle ear cavity were investigated in the fetal guinea pig near term. Perilymph lactic dehydrogenase (LDH) exhibited differential activity between fetal scalae vestibuli and tympani, and LDH, aldolase, phosphohexose isomerase and creatine phosphokinase in perilymph of particular fetal scalae were elevated in activity in activity in comparison to corresponding maternal values. Moreover, LDH displayed different isozyme patterns for antenatal and gravid perilymph. In the middle ear fluid, all of the above enzymes were encountered but varied somewhat from the quantities determined for either prenatal perilymph or maternal serum. After gravid guinea pigs were exposed to a tone of 4 kHz, 100 dB SPL for 2 hours, LDH of the fetal middle ear fluid was reduced in activity 24 hours later. The metabolic significance of the fetal distinctions in the ear fluids and the clinical implications of the current work are discussed.