[Comparative studies of lactate concentration in the perilymph, blood and cerebrospinal fluid of normal and sound exposed guinea pigs (author's transl)].

The paper deals with comparative studies of lactate concentration in the perilymph (PL) of scala tympani and of scala vestibuli, arterial and venous blood, serum and cerebrospinal fluid (CSF) of normal and sound exposed guinea pigs, special consideration having been given to possible sources of error in the methods employed. Lactate was determined enzymatically using a micromodification of the Boehringer UV-test combination adapted to 1 mul PL. The lactate concentrations in the PL of scala tympani and scala vestibuli did not differ significantly. The mean values amounted to 4.5-5.2 mM/l in the case of the opened and of the unopened subarachnoid space (Table 1). The lactate concentrations in the PL of both cochlea scales were significantly higher already ten minutes post-mortem. In the exposure experiments the animals were unilaterally exposed to sound for 1 h in an acoustically isolated system using a wide-band noise at an intensity of 120 dB SPL for one series and 2-kHz pure-tone at intensities of 112 and 122 dB SPL for two other series. We did not detect any changes in the lactate concentrations neither in the PL nor in the blood and in the CSF, following sound exposure (Table 2 and 3). The lactate concentrations of arterial and venous blood and CSF did not differ significantly. The mean values amounted to 1.4-1.8 mM/l (Table 2). However, if blood was not deproteinized or centrifuged immediately after being taken, the lactate concentration increased markedly. A comparison of the present results has shown that the lactate concentration in the PL is about three times as high as in blood and in CSF. This difference in concentration suggests that the PL lactate is of intracochlear origin and that glycolytic processes take place in the inner ear also under normal conditions. Systematic studies of additional metabolic parameters must be conducted before a definitive physiological interpretation of the present analytical results can be given.