Gene expression profiling of archival tongue squamous cell carcinomas provides sub-classification based on DNA repair genes

A subgroup of patients with squamous cell carcinoma of the head and neck (SCCHN) comprise young persons under the age of 40, who have not been heavily exposed to the classical risk factors, smoking and alcohol. The number of SCCHN in young adults, particularly tongue tumours, is increasing in several parts of the world. Here we employed a novel gene expression array methodology specifically developed for analysis of degraded RNA and investigated the expression of 502 cancer-related genes in archival paraffin-embedded SCCHN of the tongue from young (< or =40) and elderly patients (> or =50). Genes detected as de-regulated in tumours compared to non-malignant controls were in concordance with results from earlier studies of fresh frozen material. No genes were detected as significantly differentially expressed between young and old patients suggesting that the overall pathobiology of SCCHN is similar in young and old. Unsupervised clustering divided tumours into three groups, irrespective of age, where several differentially expressed DNA repair genes were a prominent separation factor. High levels of DNA repair genes associated with impaired therapeutic response to radiation, suggesting that DNA repair genes play a role in clinical outcome after radiotherapy.

High concentrations of thiosulfate in scala tympani perilymph after systemic administration in the guinea pig

CONCLUSION

High concentrations of the antioxidant thiosulfate reach scala tympani perilymph after i.v. administration in the guinea pig. Thiosulfate concentrations in perilymph remain elevated longer than in blood. This warrants further studies on the possibility of obtaining otoprotection by thiosulfate administration several hours before that of cisplatin without compromising the anticancer effect caused by cisplatin inactivation in the blood compartment.

OBJECTIVE

Thiosulfate may reduce cisplatin-induced ototoxicity, presumably by oxidative stress relief and formation of inactivate platinum complexes. This study aimed to explore to what extent thiosulfate reaches scala tympani perilymph after systemic administration in the guinea pig.

MATERIALS AND METHODS

Scala tympani perilymph (1 microl) was aspirated from the basal turn of each cochlea up to 3 h after thiosulfate administration (103 mg/kg b.w., i.v.). Blood samples were also taken. Thiosulfate was quantified by HPLC and fluorescence detection.

RESULTS

Substantial thiosulfate concentrations were found in perilymph. The area under the concentration-time curve for thiosulfate in perilymph and blood was 3100 microMxmin and 6300 microMxmin, respectively. The highest thiosulfate concentrations in perilymph were found at the first sampling at about 10 min. Due to a more rapid elimination from blood, perilymph concentrations exceeded those of blood towards the end of the experiment.

Cisplatin and oxaliplatin toxicity: importance of cochlear kinetics as a determinant for ototoxicity

BACKGROUND

Cisplatin is a cornerstone anticancer drug with pronounced ototoxicity, whereas oxaliplatin, a platinum derivative with a different clinical profile, is rarely ototoxic. This difference has not been explained.

METHODS

In HCT-116 cells, cisplatin (20 microM)-induced apoptosis was reduced by a calcium chelator from 9.9-fold induction (95% confidence interval [CI] = 8.1- to 11.7-fold), to 3.1-fold induction (95% CI = 2.0- to 4.2-fold) and by superoxide scavenging from 9.3-fold (95% CI = 8.8- to 9.8-fold), to 5.1-fold (95% CI = 4.4- to 5.8-fold). A guinea pig model (n = 23) was used to examine pharmacokinetics. Drug concentrations were determined by liquid chromatography with post-column derivatization. The total platinum concentration in cochlear tissue was determined by inductively coupled plasma mass spectrometry. Drug pharmacokinetics was assessed by determining the area under the concentration-time curve (AUC). Statistical tests were two-sided.

RESULTS

In HCT-116 cells, cisplatin (20 microM)-induced apoptosis was reduced by a calcium chelator from 9.9-fold induction (95% confidence interval [CI] = 8.1- to 11.7-fold to 3.1-fold induction) (95% CI = 2.0- to 4.2-fold) and by superoxide scavenging (from 9.3-fold, 95% CI = 8.8- to 9.8-fold, to 5.1-fold, 95% CI = 4.4- to 5.8-fold). Oxaliplatin (20 microM)-induced apoptosis was unaffected by calcium chelation (from 7.1- to 6.2-fold induction) and by superoxide scavenging (from 5.9- to 5.6-fold induction). In guinea pig cochlea, total platinum concentration (0.12 vs 0.63 microg/kg, respectively, P = .008) and perilymphatic drug concentrations (238 vs 515 microM x minute, respectively, P < .001) were lower after intravenous oxaliplatin treatment (16.6 mg/kg) than after equimolar cisplatin treatment (12.5 mg/kg). However, after a non-ototoxic cisplatin dose (5 mg/kg) or the same oxaliplatin dose (16.6 mg/kg), the AUC for perilymphatic concentrations was similar, indicating that the two drugs have different cochlear pharmacokinetics.

CONCLUSION

Cisplatin- but not oxaliplatin-induced apoptosis involved superoxide-related pathways. Lower cochlear uptake of oxaliplatin than cisplatin appears to be a major explanation for its lower ototoxicity.

Susceptibility to impulse noise trauma in different species: guinea pig, rat and mouse

CONCLUSION

The results indicate that susceptibility to impulse noise differs in the three species.

OBJECTIVE

To test the hypothesis that there is different susceptibility to impulse noise trauma in three species: the guinea pig, rat and mouse.

MATERIALS AND METHODS

Three groups of animals were exposed to the same impulse noise and the effect on cochlear pathology was examined using auditory brainstem response thresholds.

RESULTS

It was found that the rat and mouse are more sensitive to impulse noise than the guinea pig.

Effects of a single high dose of cisplatin on the melanocytes of the stria vascularis in the guinea pig

The antineoplastic drug cisplatin is known to cause a reduction in endocochlear potential. The hypothesis to be tested was whether a single high dose of cisplatin affects the melanocytes by altering the expression of melanin. Pigmented guinea pigs received a bolus injection of cisplatin (8 mg/kg as a 15-second intravenous infusion). Auditory brainstem response (ABR) thresholds and morphological analysis of the hair cells and the stria vascularis were made 96 h after injection. ABR thresholds were elevated (15-40 dB) at 12-30 kHz and a significant loss of outer hair cells in the more basal regions was found. Cisplatin caused a significantly lower density of melanin in the intermediate cells in the basal region without any signs of apoptosis. Changes in melanin content were not noted in the middle or apical cochlear regions. Significant correlations were found between melanin density, ABR threshold shifts and outer hair cell loss in the region corresponding to 30 kHz. The findings reported here further support the multiple cytotoxic effect of cisplatin on the inner ear.

Kinetics of Cisplatin and its monohydrated complex with sulfur-containing compounds designed for local otoprotective administration

The anticancer drug cisplatin can cause permanent inner ear damage. We have determined the second-order degradation rate constant, k(Nu), of cisplatin and its more toxic monohydrated complex (MHC) in the presence of each of the sulfur-containing nucleophiles N-acetyl-l-cysteine, l-cysteine methyl ester, 1,3-dimethyl-2-thiourea, d-methionine, and thiosulfate, compounds that are under evaluation for local administration to prevent cisplatin-induced ototoxicity. MHC was isolated from a hydrolysis solution of cisplatin using liquid chromatography (LC). The degradations were evaluated by measuring the disappearance of MHC and cisplatin at 37 degrees C and pH 7.4 in the presence of each of the nucleophiles using LC and photometric detection. The k(Nu) of MHC and of cisplatin was 0.044 M(-1)sec(-1) and 0.012 M(-1)sec(-1) with N-acetyl-l-cysteine, 0.24 M(-1)sec(-1) and 0.067 M(-1)sec(-1) with l-cysteine methyl ester, 0.16 M(-1)sec(-1) and 0.074 M(-1)sec(-1) with 1,3-dimethyl-2-thiourea, 0.070 M(-1)sec(-1) and 0.069 M(-1)sec(-1) with d-methionine, and 3.9 M(-1)sec(-1) and 0.091 M(-1)sec(-1) with thiosulfate, respectively. Our results suggest that thiosulfate, as being the strongest nucleophile, is a promising candidate for local application in order to reduce the inner ear content of MHC and cisplatin. However, otoprotection is a multifactorial event, and it remains to be established how important nucleophilicity is for the effectiveness of the protecting agent.

Low-dose, long-term caroverine administration attenuates impulse noise-induced hearing loss in the rat

CONCLUSION

Physiological and morphological assessments indicated that low-dose and long-term caroverine delivery might be a new approach to protect against impulse noise-induced hearing loss.

BACKGROUND

Although the exact mechanisms by which impulse noise causes hearing loss are still unclear, there is accumulating evidence that increased reactive oxygen species (ROS) production and excessive glutamate released from the inner hair cells lead to hair cell loss and consequently hearing loss. Caroverine is an antagonist of two glutamate receptors, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors in the inner ear, as well as an antioxidant.

MATERIALS AND METHODS

In this study, caroverine was delivered subcutaneously using an osmotic pump. This kind of delivery has the advantage, via continuous, long-term and low dose drug administration, of avoiding systemic side effects.

RESULTS

It was shown that caroverine could significantly protect the cochlea against impulse noise trauma.

Cochlear hair cell loss in single-dose versus continuous round window administration of gentamicin

CONCLUSIONS

Gentamicin-induced cochlear hair cell loss depends on local middle ear administration kinetics and the total drug dose. Single-dose gentamicin instillation in the middle ear is associated with a high variation in hair cell loss.

OBJECTIVE

To compare the effects of single-dose and continuous round window administration of gentamicin on cochlear hair cell loss in a guinea pig model.

MATERIAL AND METHODS

Two methods for drug administration to the inner ear were used. In groups of five animals, a total dose of 0.8 or 3.2 mg of gentamicin was either instilled as a single dose directly into the round window niche or administered continuously over a 1-week period using a pump-catheter system. Continuous administration was achieved by means of a posterior tympanotomy and subcutaneous placement of an osmotic pump fitted with a catheter. The tip of the catheter was fixed in the round window niche. One group of five animals served as controls and received a saline infusion. The animals were sacrificed after 1 week and hair cell loss was determined microscopically after dissection and phalloidin labelling of the basilar membrane and organ of Corti.

RESULTS

Quantitation of cochlear hair cell loss revealed a dose-dependent effect of gentamicin. With both treatment modalities the higher dose induced a higher percentage of hair cell loss. There was inner and outer hair cell loss in all four groups that received gentamicin. With the single-dose instillation, hair cell loss was distributed irregularly from the round window membrane towards the cochlear apex, whereas continuous administration induced hair cell loss close to the round window membrane. Single-dose instillation induced greater hair cell loss than continuous administration at the same dose. The inter-individual variation in hair cell loss was highest following single-dose instillation.

Percutaneous endoscopic gastrostomy (PEG) - a long-term follow-up study in head and neck cancer patients

Many patients with head and neck cancer experience problems related to swallowing. A retrospective study of 156 consecutive patients who received a percutaneous endoscopic gastrostomy (PEG) at a teaching hospital is presented. The results showed that 42% had complications. Fatal complications were seen in connection with PEG tube placement, but severe and minor complications could occur much later. The method of PEG tube insertion did not affect the complication rates. The spectrum of observed complications is different to that reported earlier, suggesting that the learning curve of surgeons under training could have influenced the outcome. It may be concluded that for a very sick patient a theoretically easy surgical procedure could turn into a potentially dangerous operation. It is important to select suitable candidates for a PEG. Head and neck cancer patients with a PEG need special attention in connection with the PEG tube placement and also in a long perspective, e.g. by follow-up at a nurse-led outpatient clinic.

High-Dose Cisplatin With Amifostine: Ototoxicity and Pharmacokinetics

OBJECTIVES/HYPOTHESIS

Ototoxicity is a common side effect of high-dose cisplatin treatment. Thiol-containing chemoprotectors ameliorate cisplatin ototoxicity under experimental conditions. The trial was initiated to test the efficacy of amifostine protection in high-dose cisplatin treatment (125-150 mg/m) for metastatic malignant melanoma, to correlate the ototoxic outcome with cisplatin pharmacokinetics, and to evaluate the importance of using a selective analytical method for the quantification of cisplatin.

STUDY DESIGN

Prospective study of 15 patients with stage IV malignant melanoma.

METHODS

Clinical follow-up of therapeutic response, pure-tone audiometry, and analysis of cisplatin and its monohydrated complex in blood ultrafiltrate by liquid chromatography with postcolumn derivatization were performed. Ultrafiltered blood platinum was analyzed by inductively coupled plasma mass spectrometry.

RESULTS

Ototoxicity and gastrointestinal toxicity were the most prominent side effects. Three patients ultimately required hearing aids. All patients had audiometric changes at one or more frequencies after the second treatment course, and all but one patient reported auditory symptoms. No correlation was found between hearing loss and blood cisplatin pharmacokinetics. Platinum levels determined by inductively coupled plasma mass spectrometry were higher than total platinum levels calculated from cisplatin and monohydrated complex concentrations obtained by liquid chromatography analysis.

CONCLUSION

Ototoxicity was unacceptable despite amifostine treatment. Cisplatin pharmacokinetics during the first treatment course were not predictive of hearing loss. Amifostine caused a lowering of dose-normalized area under the concentration-time curve for cisplatin and monohydrated complex. Use of the unselective inductively coupled plasma mass spectrometry analysis leads to an overestimation of active drug. Selective analysis of cisplatin is especially important when evaluating cisplatin pharmacokinetics during chemoprotector treatment.

Imaging of the guinea pig cochlea following round window gadolinium application

Precise, non-invasive determination of the aetiology and site of pathology of inner ear disorders is difficult. The aim of this study was to describe an alternative method for inner ear visualization, based on local application of the paramagnetic contrast agent gadolinium. Using a 4.7 T MRI scanner, high contrast images of all four cochlear turns were obtained 3.5 h after placing gadolinium on the round window membrane. Gadolinium cleared from the cochlea within 96 h. Auditory brainstem response measurements performed on a separate group of animals showed no significant threshold shifts after the application, indicating that gadolinium is non-toxic to the guinea pig cochlea.

Statistical methods for clinical verification of dose–response parameters related to esophageal stricture and AVM obliteration from radiotherapy

The purpose of this work is to provide some statistical methods for evaluating the predictive strength of radiobiological models and the validity of dose-response parameters for tumour control and normal tissue complications. This is accomplished by associating the expected complication rates, which are calculated using different models, with the clinical follow-up records. These methods are applied to 77 patients who received radiation treatment for head and neck cancer and 85 patients who were treated for arteriovenous malformation (AVM). The three-dimensional dose distribution delivered to esophagus and AVM nidus and the clinical follow-up results were available for each patient. Dose-response parameters derived by a maximum likelihood fitting were used as a reference to evaluate their compatibility with the examined treatment methodologies. The impact of the parameter uncertainties on the dose-response curves is demonstrated. The clinical utilization of the radiobiological parameters is illustrated. The radiobiological models (relative seriality and linear Poisson) and the reference parameters are validated to prove their suitability in reproducing the treatment outcome pattern of the patient material studied (through the probability of finding a worse fit, area under the ROC curve and chi2 test). The analysis was carried out for the upper 5 cm of the esophagus (proximal esophagus) where all the strictures are formed, and the total volume of AVM. The estimated confidence intervals of the dose-response curves appear to have a significant supporting role on their clinical implementation and use.

Dose and time-dependent protection of the antioxidant N-l-acetylcysteine against impulse noise trauma

Noise-induced hearing loss is one of the most common causes of hearing disability, and at present there is no effective biological protection or cure. Firearms and some industrial equipment can generate very high levels of impulse noise, which is known to cause sensorineural hearing loss. It has been shown that antioxidants such as N-L-acetylcysteine (NAC) can protect the inner ear from oxidative damage. The present study investigates whether NAC (i.p.) can protect the cochlea from impulse noise trauma. Rats were exposed to 50 noise pulses at 160 dB SPL peak value. Electrophysiological hearing thresholds were assessed with auditory brainstem response (ABR) up to 4 weeks after noise exposure. Animals exposed to impulse noise, without treatment of NAC, had larger threshold shifts in the frequency range 4-40 kHz than animals injected with NAC. Hair cell loss was significantly reduced using a schedule of three NAC injections in the rats. These results suggest that NAC can partially protect the cochlea against impulse noise trauma.

Care Diaries

Head and neck (H&N) cancer patients and their families meet a large number of clinicians during their long treatment period and many of them find it difficult to understand all the information given concerning their illness, treatment, and care. We have developed a care diary for these patients and their families, used also by the clinicians involved, to improve communication and patient involvement. The present survey was an evaluation of the helpfulness of those diaries. Anonymous answered questionnaires were collected from 42 H&N cancer patients, 28 family members, and 47 clinicians of different categories. Altogether 85% of the respondents stated that the care diaries had a positive effect on information, in general, and communication. It is recommended that care diaries should be implemented in the standard care for H&N cancer patients and their families. To improve the clinical value, it is particularly important to inform the clinicians on how to use the care diaries. The content and layout of the care diaries needs to be developed according to suggestions given from the respondents in this survey.

Determination and clinical verification of dose-response parameters for esophageal stricture from head and neck radiotherapy

The purpose of this work is to determine the parameters and evaluate the predictive strength of the relative seriality model. This is accomplished by associating the calculated complication rates with the clinical follow-up records. The study is based on 82 patients who received radiation treatment for head and neck cancer. For each patient the 3D dose distribution delivered to the esophagus and the clinical treatment outcome were available. Clinical symptoms and radiological findings were used to assess the manifestation of radiation-induced esophageal strictures. These data were introduced into a maximum likelihood fitting to calculate the best estimates of the parameters used by the relative seriality model (D50 = 68.4 Gy, gamma = 6.55, s = 0.22). The uncertainties of these parameters were also calculated and their individual influence on the dose-response curve was demonstrated. The best estimate of the parameters was applied to 58 patients of the study material and their esophageal stricture induction probabilities were calculated to illustrate the clinical utilization of the calculated parameters. The calculation of the biological effective dose (BED) appeared to be significantly sensitive to the applied fractionation correction for complex treatment plans. The relative seriality model was proved suitable in reproducing the treatment outcome pattern of the patient material studied (probability of finding a worse fit = 61.0%, the area under the ROC curve = 0.84 and chi2 test = 0.95). The analysis was carried out for the upper 5 cm of the esophagus (proximal esophagus) where all the strictures are formed. Radiation-induced strictures were found to have a strong volume dependence (low relative seriality). The uncertainties of the parameters appear to have a significant supporting role on the estimated dose-response curve.

Intracochlear administration of thiourea protects against cisplatin-induced outer hair cell loss in the guinea pig

Amelioration of cisplatin-induced side-effects is of great clinical importance. Local administration of a cytoprotective agent to the inner ear offers a possibility to prevent cisplatin-induced ototoxicity without risk of interference with the antitumour effect. The ideal substance for local administration has yet to be identified. Thiourea (TU) has unique properties that make it an interesting candidate. This study was initiated to test the hypothesis that TU given by local administration protects against cisplatin ototoxicity in the guinea pig. After baseline auditory brainstem response (ABR) assessment, the left cochlea was implanted with a microtip catheter connected to an osmotic pump filled with either 27 mg/ml TU in artificial perilymph (AP), or AP administered for the full duration of the study. Three days post-implant, animals with normal ABRs received an intravenous injection of 8 mg/kg body-weight cisplatin. Five days after the cisplatin treatment ABRs were reassessed, animals decapitated and bilateral cytocochleograms prepared. TU-treated ears demonstrated significantly lower outer hair cell (OHC) loss as compared to contralateral untreated ears, and significantly lower OHC loss compared to AP-treated ears. ABR threshold shift did not differ significantly between the two groups. It can be postulated that TU demonstrates partial protection against cisplatin-induced ototoxicity.

Stricture of the proximal esophagus in head and neck carcinoma patients after radiotherapy

BACKGROUND

It is well recognized that many patients with head and neck carcinoma have problems with food intake and malnutrition. The objective of the current study was to determine the clinical pattern of patients with nonneoplastic stricture of the upper esophagus after radiotherapy for head and neck carcinoma.

METHODS

A retrospective chart study of 22 patients with stricture of the proximal esophagus diagnosed between 1993 and 1999 at Karolinska Hospital was performed. The dose volume histograms of the first 2 cm and 5 cm, respectively, of the proximal esophagus were calculated.

RESULTS

Five of the patients (23%) had total obliteration. The first 2 cm of the esophagus received at least 60 grays (Gy) in > 80% of the volume. Radiation injury was not reported to occur at doses < 60 Gy. There was a correlation found between dysphagia during radiotherapy and the development of proximal esophageal stricture. Stricture was diagnosed 1-60 months (median, 6 months) after radiotherapy. In 18 patients, the stricture was treated with single or repeated endoscopic dilation. These treatments allowed a nearly normal diet in 78% of the patients.

CONCLUSIONS

Stricture of the upper esophagus is one deglutition disorder that is reported to occur after radiotherapy for head and neck carcinoma. In the current study, the authors emphasize the importance of knowing the tolerance of the normal esophagus to irradiation as well as early diagnosis of stricture of the proximal esophagus because this condition may lead to physical and emotional distress.

Ototoxicity, nephrotoxicity and pharmacokinetics of cisplatin and its monohydrated complex in the guinea pig

PURPOSE

To evaluate and compare the ototoxicity and nephrotoxicity of cisplatin and cis-diammineaquachloroplatinum(II) ion (monohydrated complex of cisplatin, MHC, formed in vivo by hydrolysis of cisplatin) after their separate administration to guinea pigs.

METHODS

A dose of 4 mg/kg body weight of MHC was deemed suitable for the toxicity evaluation after dose titration. Electrophysiological hearing thresholds (auditory brainstem response, ABR), plasma creatinine and weight were measured in three groups of animals before and after receiving MHC 4 mg/kg (0.0141 mmol/kg), cisplatin 4.24 mg/kg (0.0141 mmol/kg, i.e. equimolar dose) or cisplatin 8 mg/kg (0.0267 mmol/kg) as an i.v. bolus injection. Cisplatin and MHC were analysed using liquid chromatography with post-column derivatization.

RESULTS

Administration of MHC 4 mg/kg caused a moderate ABR threshold shift, a significant increase in creatinine and a significant weight loss, changes similar to those seen after administration of cisplatin 8 mg/kg. Animals given cisplatin 4.24 mg/kg had a slight increase in creatinine, but had no ABR threshold shift and gained weight during the experiment. The pharmacokinetic parameters of cisplatin and MHC were estimated after administration of cisplatin 4.24 mg/kg and MHC 4 mg/kg. The area under the blood-ultrafiltrate concentration versus time curve (AUC) for cisplatin after administration of MHC 4 mg/kg was 23% (56+/-5.0 micro g.min.ml(-1)) (means+/-SD) of that after administration of cisplatin 4.24 mg/kg (240+/-25 micro g.min.ml(-1)). The AUC for MHC after administration of cisplatin 4.24 mg/kg was 20% (30+/-4.9 micro g.min.ml(-1)) of that after administration of MHC 4 mg/kg (149+/-26 micro g.min.ml(-1)).

CONCLUSIONS

MHC 4 mg/kg causes ototoxicity, nephrotoxicity and weight loss when administered to guinea pigs. The toxic effects were similar to those seen after administration of cisplatin 8 mg/kg and higher than those seen after administration of cisplatin 4.24 mg/kg.

Local administration of antioxidants to the inner ear. Kinetics and distribution(1)

Round window (r.w.) administration of drugs involves the delivery of medication directly into the inner ear via the r.w. membrane, avoiding a systemic effect of the therapy. Earlier experimental studies suggest that a number of antioxidants and scavengers hold promise for ameliorating the tissue damaging capacity of reactive oxygen species in some acquired cochlear disorders. D-Methionine and thiourea are two small sulfur-containing molecules with an antioxidative and scavenging effect. The passage through the r.w. of radioactive D-methionine and thiourea administered by 1 h infusion to the r.w. was studied in a rat model. Levels of the tracers were measured in scala tympani perilymph (PLT) 17-254 min after r.w. administration. Both tracers pass the r.w. membrane readily. Peak levels were found in the earliest taken samples after the administration. The radioactivity in PLT of the basal turn reached a peak to about 1.5-1.9% of the irrigating medium radioactivity. Following the r.w. administration, the concentration of radioactive D-methionine and thiourea declined with a terminal half-life of 0.57 and 0.77 h, respectively. The distribution of the tracers at the cellular level was analyzed by autoradiography. The most intense expression was found in the lateral wall of the cochlea. It can be postulated that local delivery to the cochlea of D-methionine and thiourea via the r.w. gives high local concentrations of the substances in PLT in the basal turn.

Evaluation of anesthesia effects in a rat animal model using otoacoustic emission protocols

Anesthesia effects on otoacoustic emission (OAE) recordings were evaluated in a group of 72 Sprague-Dawley rats (mean weight 225+/-20 gr). Two anesthesia dosages (high and normal) and two anesthetic protocols (ketamine-xylazine, ketamine-xylazine-atropine) were tested. Transient evoked OAE (TEOAE) and distortion product OAE (DPOAE) responses were recorded in 10 min intervals, for a total period of 60 min. Analyses of the data with repeated measure models indicated the following: (1) The animals receiving a high dose of anesthesia (cumulative dose 66.6 mg of ketamine and 13.2 mg of xylazine/kg of body weight) presented significant alterations of the TEOAE response level and the signal to noise ratio at 3.0 kHz; (2) the animals receiving a normal dose of ketamine-xylazine anesthesia (cumulative dose 50 mg of ketamine and 10 mg of xylazine/kg of body weight) presented TEOAE and DPOAE responses invariant in terms of time; (3) significant differences were observed in the DPOAE responses from animals anesthetized with ketamine-xylazine and ketamine-xylazine-atropine. The data support the hypothesis that the ketamine anesthesia OAE suppressing mechanism is related to middle-ear mechanics.