Cathepsin D activity in otosclerotic bone and perilymph

Otosclerotic bone and perilymph samples obtained during stapedectomy operations from patients suffering from pure conductive hearing loss of at least 40 dBs air-bone gap at 500 Hz. Control perilymph samples derived from patients suffering from round window membrane rupture or Meniere's disease. Enzyme activities were determined using a synthetic fluorogenic substrate by fluorescence spectrophotometry. No significant differences have been found between the protein content of otosclerotic and normal or non-otosclerotic perilymph samples. Cathepsin D activity was significantly higher (p less than 0.001) in the otosclerotic perilymph samples. Otosclerotic stapes footplate contained more activity than normal meatal cortical bone as well, though the difference was not significant. Biological significance of the elevated Cathepsin D activity must be considered.

Early effects of acetazolamide on anionic activities of the guinea pig endolymph: evidence for active function of carbonic anhydrase in the cochlea

The effect of acetazolamide (ACZ) on HCO3- and Cl- activities in inner ear fluid was investigated by ion-selective microelectrode methods. The endocochlear potential, at 81.6 +/- 1.5 mV under normal conditions, was reduced by 4.9 +/- 0.9 mV in 30 min following the ACZ injection. The HCO3- concentrations by 11.5 +/- 1.7 mM in 30 min, while the change of Cl- level was not consistent but showed a tendency toward slight increase in average. The calculated PCO2 in endolymph was 39.6 mmHg. ACZ induced a constant elevation of the endolymph PCO2, with an increase in the venous PCO2 during the initial 20 min and thereafter the endolymph PCO2 attained a plateau despite the continuous increase of the venous PCO2. We postulate that the HCO3- secretion into the endolymph is mediated by carbonic anhydrase (CAH) and is decreased by ACZ due to the inhibition of CAH.

[Total lactate dehydrogenase activity of perilymph, plasma and cerebrospinal fluid in unstressed and noise stressed guinea pigs]

The total activity of lactate dehydrogenase (LDH) of perilymph (PL), plasma, and cerebrospinal fluid (CSF) of unexposed and sound-exposed guinea pigs was examined with due consideration of the principal sources of error. To test the purity of PL samples, protein, potassium, and sodium were determined simultaneously (Table 1). The LDH was analysed fluorometrically. It was found that there are considerable differences in the LDH activities of PL, CSF, and plasma (Table 2). The mean activity of PL was three to four times higher than that of CSF and only about half that of plasma. No significant difference was found between the PL in scala tympani and scala vestibuli. The most frequent LDH values of the individual fluids (Fig. 2) were somewhat lower than the mean values calculated. Immediately (less than or equal to 60 min) after exposing the animals to wide-band noise at an intensity of 140 dB SPL for 10 min, the mean PL values of the scala tympani and scala vestibuli were found to be somewhat higher than in unexposed animals (Table 3). Eighteen hours after the exposure, slightly higher activity was only detectable in PL of the scala vestibuli. The differences were not found to be significant. The LDH values of CSF and plasma remained unchanged both less than or equal to 60 min and 18 h after noise exposure.

Lysosomal hydrolases in middle ear effusions

Biochemical studies of middle ear effusions have demonstrated generally higher levels of certain hydrolytic and oxidative enzymes in mucoid fluids when compared to serous. We have extended these studies by analyzing middle ear effusions for the content of a large number of lysosomal hydrolases. The mean specific activity for alpha-glucosidase in mucoid fluids was found to be ten times that for serous fluids while alpha-mannosidase, beta-glucuronidase, hexosaminidase, acid phosphatase, beta-galactosidase, alkaline phosphatase, and lactate dehydrogenase were found to be three to five times greater in mucoid than serous effusions. In this study the specific enzyme activities for lysosomal hydrolases from purulent effusions were found to be intermediate between the activities in serous and mucoid effusions. No significant correlation was found between the specific activities of lysosomal hydrolases and the presence or absence of bacteria in mucoid or serous middle ear effusions. The hexosaminidase isozyme distribution was found to be identical for serous and mucoid fluids and similar to that found in human serum. However, the isozyme pattern of beta-glucuronidase in mucoid effusions was significantly different than that in normal human serum as mucoid fluids contain a large amount of an anionic isoenzyme of beta-glucuronidase that is barely detectable in human serum.

Alteration of oxidative enzymes (LDH and MDH) in perilymph after noise exposure

Chinchillas were exposed to noise (123 dB, 1/2 h, 700--2800 Hz). The activity of lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) was studied immediately after exposure or 1, 7, 14, 21, or 28 days later. LDH activity in perilymph doubled immediately after exposure, gradually decreasing to control values in about a month. The activity of MDH not only doubled immediately after the exposure but continued to rise for at least another 24 h, reaching a peak value of 3.5 times normal at 24 h. The activity was still 1.6 times normal even after a month of recovery. The enzyme activity of serum and CSF remained within the control range throughout the experimental period except for an initial increase of serum enzyme activity due to anesthetic. The results demonstrate that the morphological changes induced by a noise exposure that is known to produce permanent threshold shift (PTS) are reflected in a significant elevation of oxidative enzymes in perilymph. Possible mechanisms of the elevation of enzymes in perilymph are discussed.

Experimental alteration of physiological state of inner ear fluids

Mechanisms of endolymphatic hydrops formation in the inner ear are not yet fully understood. The available knowledge of the composition and the function of inner ear fluids, of mechanisms for maintenance of microhomeostasis, and the possible factors responsible for hydrops formation were reviewed. The nature of the functional barrier systems of the inner ear was investigated by measuring the amount of intravenously or intracisternally injected test substances which entered the perilymph. Based on studies of the osmotic relationship between the blood and the perilymph, an hypothesis of hydrops formation is proposed. The hypothesis predicts an osmotic imbalance, resulting from an upset of the homeostasis between the fluid compartments and the tissues of the inner ear, as a factor responsible for endolymphatic hydrops formation. An osmotic imbalance can be induced by various experimental conditions including metabolic disorders. The results of animal experiments strongly suggest the necessity of further survey of metabolic imbalance in Ménière's patients.

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.

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.

[A biochemical and cytological explanation of cochlear otospongiosis]

In a study of 250 otosclerotic perilymphatic fluids, it was found statistically that in the presence of developing inner ear deafness, 90% of cases will demonstrate increased trypsin activity. Conversely, elevated antitrypsin levels are found in the absence of developing inner ear deafness.

Aminotransferases in post-mortem cochlear fluids

Aspartate and alanine aminotransferase (ASAT, ALAT) activities were measured in human post-mortem sera, cerebrospinal fluid (CSF), perilymph and endolymph. Due to heart and/or liver morbidity during a terminal illness, the ASAT and ALAT serum activities were considerably increased as compared with normal and both were 20--30 times higher (p less than 0.001) than in CSF or inner ear fluids. CSF and inner ear fluids showed mutually similar values.