Zur Glukose-, Pyruvat- und Laktatkonzentration von Perilymphe, Blut und Liquor cerebrospinalis unbelasteter und schallbelasteter Meerschweinchen in �thylurethannarkose

Abstract

Glucose, pyruvate, and lactate of perilymph (PL), blood, and cerebrospinal fluid (CSF) of unexposed and sound-exposed guinea pigs under ethyl urethane anesthesia were examined with due consideration of the principal sources of error. The animals had fasted for 15--20 h before the experiment to stabilize the blood glucose level. The metabolites were determined enzymatically by means of fluorescence measurements. It was found that the glucose levels depend not only on ingestion but also on the duration of anesthesia of the animals before sampling. The mean values of the scala tympani and scala vestibuli PL and CSF did not differ significantly, being about half those of blood or plasma immediately (10--20 min) after introducing anesthesia (Table 2). This concentration difference is in disagreement with the original ultrafiltration hypothesis of PL, suggesting a blood-PL barrier for glucose. The dependence on the duration of anesthesia and on the animals' ingestion before sampling appears to be an important cause of the differences in glucose data published in literature hitherto. No influence of anesthesia on pyruvate and lactate concentrations was observed. Data obtained on unexposed control animals (Tables 3 and 4) confirmed our earlier metabolite findings (Scheibe et al. 1976, 1981). No major changes in glucose, pyruvate, and lactate concentration of PL, blood, and CSF were detectable immediately after 1 h of exposure to wide-band noise at an intensity of 120 dB SPL. The present lactate findings confirmed our earlier exposure experiments (Scheibe et al. 1976), but they did not agree with the information given by Schnieder (1974).

Noise-Induced Cochlear Hypoxia Is Intensity Dependent, Correlates with Hearing Loss and Precedes Reduction of Cochlear Blood Flow

“…Biochemical studies related to energy metabolism such as ATP levels [22], metabo lites and enzymes [22][23][24][25][26] have failed to dem onstrate any effects of exposure to nontraunratic noise [for reviews, see 22,[27][28][29][30][31], In addition, an increase in deoxyglucose uptake, which could demonstrate an increase in me tabolism in response to broad-band noise at intensities of up to 100 dB [32], was not observed in the auditory tissues of the guinea pig. However, the changes observed here fol lowed higher levels of noise exposure.…”

Neuroglobin Expression in the Mammalian Auditory System

“…However, questions remain about the relative contributions of the glycolytic and oxidative pathways to the synthesis and maintenance of ATP levels in the inner ear. Glycolysis results in the formation of lactate, but since attempts to measure lactate in the cochlea have failed [48], it has long been assumed that low level aerobic metabolism is the primary source of cochlear ATP. On the other hand, there is evidence that outer hair cells deprived of glucose ex vivo generate ATP, which suggests that these sensory cells may also possess unidentified intracellular metabolic substrates that can augment oxidative phosphorylation under hypoxic conditions [41].…”