Differential uptake of salicylate in serum, cerebrospinal fluid, and perilymph

After intraperitoneal administration of salicylate in anesthetized rats and guinea pigs, we found that salicylate levels in perilymph (PL) are closely related to both drug levels in cerebrospinal fluid (CSF) and in serum, with higher levels systematically observed in PL than in CSF. Further analysis suggests that salicylate is not passively transported into PL across CSF but, rather, is transported from blood directly to PL. The time course of salicylate uptake in rats reveals maximum levels at 1 1/2 hours (serum) and two to four hours (CSF and PL). On the other hand, salicylate uptake into serum and CSF of guinea pigs exhibits a longer time course, with maximum levels reached at four hours (serum) and five hours (CSF). These data, not previously available, are basic to our understanding of salicylate-related auditory effects.     

Fluorescein Kinetics in Perilymph and Blood: A Fluorophotometric Study

A modified slit lamp fluorophotometer was used to determine fluorescein concentration changes in the perilymph, cerebrospinal fluid and blood of chinchillas after intravenous injection of 0.2 ml of fluorescein sodium. This new technique provides a means of determining quantitative changes of fluorescein concentration in the perilymph without the need to withdraw fluid samples through the round window membrane or cochlear wall. Fluorescein was observed to enter the perilymph between 1 and 2 minutes after injection, and it reached its peak concentration in a mean time of 23 minutes. The mean peak concentration was 4.20x10^?6 g/ml. Both increasing and decreasing fluorescein concentration changes in the perilymph followed an exponential time course. Although the observations of cerebrospinal fluid fluorescence were thought to represent a composite of the fluorescence of the cerebrospinal fluid itself and the underlying brain stem blood vessels, the peak fluorescence did not exceed that observed in the perilymph. These observations support the view that most of the perilymph is produced in the cochlea by ultrafiltration from the cochlear blood vessels. The slit lamp fluorophotometer appears to be a satisfactory means of recording fluorescein concentration changes in the perilymph without disturbing the cochlear physiology by penetrating the labyrinth to obtain fluid samples.     

Concentration of salicylate in serum and perilymph of the chinchilla

The concentration of salicylate in serum and perilymph was measured in chinchillas after intraperitoneal administration of sodium salicylate. Serum salicylate concentration peaked 2 to 4 hours after a single injection. Clearance was approximately complete after 16 hours. The within-subject variability of serum concentration 4 hours after injection was very low. Subject weight significantly affected serum salicylate concentration, with heavier animals showing higher serum levels. The relationship of perilymph to serum salicylate concentration was approximately linear, with a high correlation between measures.     

Effects of glycerol on sodium and potassium concentrations in guinea pig perilymph

Summary Serum, cerebrospinal fluid (CSF), scala vestibuli perilymph, and scala tympani perilymph were collected from 85 normal guinea pigs both before and after i.v. administration of glycerol (1 ml/kg), and the sodium and potassium concentrations were assessed using a microflame photometer. Marked increases in sodium concentrations were observed in scala tympani perilymph and CSF, while there was a slight decrease in the serum and there was no significant change in scala vestibuli perilymph. These increases in sodium concentrations are considered to occur in the dehydration process in the body fluids mentioned above. On the other hand, increase in the potassium concentrations was found only in scala vestibuli perilymph and thus cannot be explained by simple dehydration process. This potassium elevation in scala vestibuli perilymph should be understood by further experiment on endolymph. It became evident that scala vestibuli perilymph differs from scala tympani perilymph and CSF in the dynamics of electrolytes after glycerol administration. In this regard, the nature of the scala vestibuli as fluid space should be studied in future. The above findings obtained in the present study may imply the significance in elucidating the glycerol effect on hearing of endolymphatic hydrops case.This study was funded in part by a grant from the Ministry of Education, Science, and Culture, Japan     

Effects of intravenous glycerol injection on inner ear fluid electrolytes

Under sodium pentrobarbital anesthesia (20-30 mg/kg, i.p.), normal guinea pigs received an intravenous injection of glycerol (1.0 ml/kg). Serum, cerebrospinal fluids (CSF) and inner ear fluids were collected from the scala tympani perilymph, scala vestibuli perilymph and the scala media endolymph. The sodium and potassium concentrations were assessed using microflame photometry. Increases in sodium concentration were found in the CSF and the scala tympani perilymph; no significant changes were observed in the serum, scala vestibuli perilymph or the scala media endolymph. These sodium increases were considered to be a result of the dehydration process caused by the osmotic agent glycerol. Increases in potassium concentration were found only in the scala vestibuli perilymph.     

Transport characteristics of the blood—Perilymph barrier

The inner ear must maintain a delicate homeostasis to preserve high sensitivity to acoustic and vestibular inputs. Various experimental conditions were imposed upon chinchillas to help identify these homeostatic mechanisms for the inner ear fluids. Radioactive ions (sodium, chloride, and calcium) pass into perilymph more slowly than they pass into cerebrospinal fluid or aqueous humor. The concentration of glucose in perilymph relative to that in serum was found to be quite constant (about 45 per cent) over a wide range of serum values (130-943 mg/dl) generated by continuous intravenous infusion. The transport of albumin into perilymph was very slight after injection of the radioactive protein intravenously. Osmotic agents cause an efflux of water from perilymph into a relatively hypertonic circulating blood, resulting in a secondary elevation of perilymph osmolarity. Recent findings relating to cyclic AMP metabolism and the possible role of this second messenger in the regulation of inner ear fluid metabolism are discussed. A new hypothesis that excess cyclic AMP in the inner ear may be related to endolymphatic hydrops is presented.     

Amino acid profiles in inner ear fluids and cerebrospinal fluid

The levels of 19 amino acids in utricular endolymph, vestibular and cochlear perilymph, and cerebrospinal fluid of guinea pigs were determined using gradient elution reverse phase high performance liquid chromatography of the o-phthaldialdehyde-ethanethiol adducts with fluorescence detection. Aspartate and glutamate were significantly higher in endolymph than in perilymph, in agreement with earlier results on cochlear fluids based on enzymatic fluorometric techniques. All other amino acids tested were significantly lower in the endolymph, in most cases by an order of magnitude. Vestibular perilymph and perilymph of scala vestibuli are virtually identical. Amino acid levels were all higher in perilymph of scala vestibuli than in cerebrospinal fluid; two by an order of magnitude. All differences were statistically significant, with the exception of aspartate. Amino acid levels in perilymph of scala tympani were highly variable, dependent upon sampling technique, and no definite values are therefore presented. Comparisons with results from other laboratories, technical pitfalls, and possible implications and interpretations of the results are presented.     

Whole-body autoradiography of [3H]dihydrostreptomycin in guinea pigs and rats: the labelling of the inner ear in relation to other tissues

[3H]Dihydrostreptomycin was given intramuscularly to young pigmented guinea pigs and rats. Whole-body autoradiography, combined with densitometric measurement of the blackening of the autoradiograms, and liquid scintillation counting were used to determine the levels of radioactivity in the inner ear in relation to blood and other tissues. It was found that there was an accumulation of radioactivity in the perilymph of both the cochlear and vestibular parts of the labyrinth. The labelling of the endolymph was weak. The levels of radioactivity in the membranous linings of the labyrinth including the areas covered with the neuroepithelial structures, were about the same as in the perilymph. The general distribution pictures were characterized by a localization of radioactivity in extracellular tissues, such as cartilages and connective tissues and by strong labelling of the kidney cortex. The preferential uptake in the perilymph indicates a route by which the inner ear hair cells can be exposed to high levels of aminoglycoside antibiotics.     

Perilymph composition in scala tympani of the cochlea: influence of cerebrospinal fluid

A commonly used technique to obtain cochlear perilymph for analysis has been the aspiration of samples through the round window membrane. The present study has investigated the influence of the volume withdrawn on sample composition in the guinea pig. Samples of less than 200 nl in volume taken through the round window showed relatively high glycine content, comparable to the level found in samples taken from scala vestibuli. If larger volumes are withdrawn, lower glycine levels are observed. This is consistent with cerebrospinal fluid (having a low glycine content) being drawn into scala tympani through the cochlear aqueduct and contaminating the sample. The existence of a concentration difference for glycine between scala tympani perilymph and cerebrospinal fluid suggests the physiologic communication across the cochlear aqueduct is relatively small in this species. The observation of considerable exchange between cerebrospinal fluid and perilymph, as reported in some studies, is more likely to be an artifact of the experimental procedures, rather than of physiologic significance. Alternative sampling procedures have been evaluated which allow larger volumes of uncontaminated scala tympani perilymph to be collected.     

Determination of lactate dehydrogenase isozymes in the cochleae of guinea pigs

The isozymes of lactate dehydrogenase (LDH) in perilymph and homogenates from vascular stria, Corti's organ, and vestibular membrane of healthy guinea pigs were determined with the micro-homogenate electrophoresis technique. The results were compared with those in serum and cerebrospinal fluid. It was found that electrophoretogram of individual homogenate or perilymph, which showed the isozymes of LDH, had a special pattern different from that in the serum. The factors which might affect LDH in perilymph had been discussed.     

In vivo observation of dynamic perilymph formation using 4.7 T MRI with gadolinium as a tracer

OBJECTIVE: To investigate the pharmacokinetics of gadolinium in the perilymphatic fluid spaces of the cochlea in vivo using high-resolution MRI to obtain information concerning perilymph formation. MATERIAL AND METHODS: A Bruker Biospec Avance 47/40 experimental MRI system with a magnetic field strength of 4.7 T was used. Anesthetized pigmented guinea pigs were injected with the contrast agent Gd-diethylenetriaminepentaacetic acid-bismethylamide and placed in the magnet. The signal intensity of Gd in the tissues was used as a biomarker for dynamic changes in the perilymphatic fluid. RESULTS: The most rapid uptake of Gd in the perilymphatic fluid spaces occurred in the lower part of the modiolus, followed by the second turn of the scala tympani. Within the scala tympani, the distribution of Gd in the basal turn was significantly lower than that in the other turns. Destruction of the cochlear aqueduct was followed by an increase in Gd uptake in the perilymph instead of a reduction. CONCLUSIONS: These findings offer further evidence that the pervasive perilymphatic fluid derives from the cochlear blood supply via the cochlear glomeruli, which are in close proximity to the scala tympani within the modiolus, and the capillary in the spiral ligament. Cerebrospinal fluid communicates with perilymph via the cochlear aqueduct but is not the main source of perilymph. These findings are of relevance to the treatment of inner ear diseases, as well as to our understanding of the flow and source of perilymphatic fluid.     

In Vivo Observation of Dynamic Perilymph Formation Using 4.7 T MRI with Gadolinium as a Tracer

Objective—To investigate the pharmacokinetics of gadolinium in the perilymphatic fluid spaces of the cochlea in vivo using high-resolution MRI to obtain information concerning perilymph formation. Material and Methods—A Bruker Biospec Avance 47/40 experimental MRI system with a magnetic field strength of 4.7 T was used. Anesthetized pigmented guinea pigs were injected with the contrast agent Gd-diethylenetriaminepentaacetic acid-bismethylamide and placed in the magnet. The signal intensity of Gd in the tissues was used as a biomarker for dynamic changes in the perilymphatic fluid. Results—The most rapid uptake of Gd in the perilymphatic fluid spaces occurred in the lower part of the modiolus, followed by the second turn of the scala tympani. Within the scala tympani, the distribution of Gd in the basal turn was significantly lower than that in the other turns. Destruction of the cochlear aqueduct was followed by an increase in Gd uptake in the perilymph instead of a reduction. Conclusions—These findings offer further evidence that the pervasive perilymphatic fluid derives from the cochlear blood supply via the cochlear glomeruli, which are in close proximity to the scala tympani within the modiolus, and the capillary in the spiral ligament. Cerebrospinal fluid communicates with perilymph via the cochlear aqueduct but is not the main source of perilymph. These findings are of relevance to the treatment of inner ear diseases, as well as to our understanding of the flow and source of perilymphatic fluid.     

Pharmacokinetical, histological, and histochemical investigation on the ototoxicity of gentamicin, tobramycin, and amikacin (author's transl)

The pharmacokinetics of gentamicin, tobramycin, and amikacin in the inner ear fluids and serum of the guinea pig were studied. The concentrations of these antibiotics were determined by a microbiological method and could be confirmed by the use of 14C-labeled gentamicin. Retention was clearly demonstrated in perilymph and endolymph, whereas there was no retention in the cerebrospinal fluid and the compartments of the eye. A linear relation between concentrations in the perilymph and dosage of gentamicin was ascertained. There was no difference between the concentration of drug in endolymph and that in perilymph. The concentrations of these antibiotics in the perilymph were symmetrical and many times higher than those in the brain. Long-term treatment did not influence the pharmacokinetics of the three antibiotics in the inner ear. However, increased levels of drug in the inner ears in animals with uremia and in some animals with otitis media explained the increased ototoxicity that was observed in histological investigations of these two conditions. Cisternal puncture and diuretics did not change the concentrations of aminoglycoside antibiotics in the inner ear. In large experimental series the hair cell degeneration pattern of the new aminoglycoside antibiotics was determined by the surface preparation technique as well as the influence of the different factors upon this pattern. A prophylactic effect on the ototoxicity of the aminoglycoside antibiotics could not be found in the 2,3-dimercaptopropanol, but by dividing the daily dosage administered. Young guinea pigs were generally not very sensitive to gentamicin, in some cases however much more. Late ototoxicity could not be found after administration of gentamicin. The pharmacokinetical and especially the histological investigations allowed an evaluation of the ototoxicity of the new aminoglycoside antibiotics. By histochemical investigations no influence of the new aminoglycoside antibiotics upon the amount of unspecific esterases and alkaline phosphatase in the inner ear could be detected, but an increase of the amount of acid phosphatase in slightly damaged outer hair cells.     

Hereditary deafness in the cat. Free amino acid and sugar content in the perilymph

The free amino acid and sugar content of cat perilymph was studied from 11 normal and 17 deaf ears, and compared with simultaneous estimations from cerebrospinal fluid and serum. Each fluid has a distinctive amino acid composition, whilst glucose was the only saccharide demonstrable. The functional status of the cochlea did not influence the biochemical parameters studied.     

On sources of error in the biochemical study of perilymph (guinea-pig)

Contamination of perilymph with other fluids (cerebrospinal fluid, tissue fluid, blood, endolymph) together with sampling, anaesthesia, surgical intervention or food intake of the animals may considerably affect the analytical result. The numerous possible artefacts seem to be the main reason why varying values are given in the literature for the same chemical component of perilymph. This is also partly true of cerebrospinal fluid and blood. The effect of some sources of error on selected chemical components of perilymph, cerebrospinal fluid and blood is briefly summarized.     

On sources of error in the biochemical study of perilymph (guinea-pig)

Summary Contamination of perilymph with other fluids (cerebrospinal fluid, tissue fluid, blood, endolymph) together with sampling, anaesthesia, surgical intervention or food intake of the animals may considerably affect the analytical result. The numerous possible artefacts seem to be the main reason why varying values are given in the literature for the same chemical component of perilymph. This is also partly true of cerebrospinal fluid and blood. The effect of some sources of error on selected chemical components of perilymph, cerebrospinal fluid and blood is briefly summarized.     

Species differences in inner ear fluids

Summary Inner ear fluids of guinea pigs and cats were analyzed for sodium, potassium, chloride, glucose, and total protein to determine species differences in chemical compositions. In the scala vestibuli perilymph and scala tympani perilymph, sodium, potassium, and choride levels in the guinea pig were lower than in the cat. The protein levels in the scala vestibuli perilymph and scala tympani perilymph of the guinea pig were lower than those of the cat. The glucose levels in the guinea pig were higher in the scala vestibuli perilymph and scala tympani perilymph, as compared to findings in the cat. Regarding the utricular endolymph, there were significant differences between guinea pigs and cats in sodium and potassium concentrations; the concentration in the former being higher in sodium and lower in potassium. These findings are pertinent for the phylogenetic studies on inner ear fluid biochemistry.This work was supported by Research Grant No. ROI-NS1026801 from the National Institute of Neurological Diseases and Strokes, USA     

Effect of peroral glycerol administration on inner ear fluid electrolytes of guinea pigs

After the oral administration of 50% glycerol (12 mL/kg), serum, CSF and inner ear fluids from scala tympani perilymph, scala vestibuli perilymph, and scala media endolymph were collected from normal guinea pigs under sodium pentobarbital anesthesia (25-35 mg/kg). The sodium and potassium concentrations were determined by microflame photometry. Increases in sodium concentrations were found in CSF, scala tympani perilymph, scala vestibuli perilymph, and cochlear endolymph. No significant change was observed in the serum. These sodium increases were considered to be due to the dehydration caused by the osmotic action of glycerol. Potassium concentration was increased only in scala tympani perilymph. Oral administration of glycerol was found to be more gradual and effective in dehydration compared to intravenous injection.     

Pharmakokinetische,histologische und histochemische Untersuchungen zur Ototoxizität des Gentamicins,Tobramycins und Amikacins

Summary The pharmacokinetics of gentamicin, tobramycin, and amikacin in the inner ear fluids and serum of the guinea pig were studied. The concentrations of these antibiotics were determined by a microbiological method and could be confirmed by the use of¹⁴C-labeled gentamicin. Retention was clearly demonstrated in perilymph and endolymph, whereas there was no retention in the cerebrospinal fluid and the compartments of the eye. A linear relation between concentrations in the perilymph and dosage of gentamicin was ascertained. There was no difference between the concentration of drug in endolymph and that in perilymph. The concentrations of these antibiotics in the perilymph were symmetrical and many times higher than those in the brain. Long-term treatment did not influence the pharmacokinetics of the three antibiotics in the inner ear. However, increased levels of drug in the inner ears in animals with uremia and in some animals with otitis media explained the increased ototoxicity that was observed in histological investigations of these two conditions. Cisternal puncture and diuretics did not change the concentrations of aminoglycoside antibiotics in the inner ear. In large experimental series the hair cell degeneration pattern of the new aminoglycoside antibiotics was determined by the surface preparation technique as well as the influence of the different factors upon this pattern. A prophylactic effect on the ototoxicity of the aminoglycoside antibiotics could not be found in the 2,3-dimercaptopropanol, but by dividing the daily dosage administered. Young guinea pigs were generally not very sensitive to gentamicin, in some cases however much more. Late ototoxicity could not be found after administration of gentamicin. The pharmacokinetical and especially the histological investigations allowed an evaluation of the ototoxicity of the new aminoglycoside antibiotics. By histochemical investigations no influence of the new aminoglycoside antibiotics upon the amount of unspecific esterases and alkaline phosphatase in the inner ear could be detected, but an increase of the amount of acid phosphatase in slightly damaged outer hair cells.

Herrn Prof. Dr. med. P. Falk zum 70. Geburtstag in Verehrung gewidmet     

Intraoperative assessment of perilymphatic fistulas with intrathecal administration of fluorescein

OBJECTIVES: Assessment of perilymphatic fistulas remains a diagnostic problem. Because of a lack of reliable clinical tests, exploratory tympanotomy is necessary to detect membrane leaks in the middle ear. To improve objectivity in the intraoperative visualization of perilymphatic fistulas, we used intrathecal fluorescein for perilymph staining to increase the sensitivity and specificity of diagnosis of perilymphatic fistulas. STUDY DESIGN: Prospective study in the setting of a tertiary, referral, and academic center. METHODS: Twenty-eight patients with suspected traumatic, idiopathic, iatrogenic, or inflammatory perilymphatic fistulas were admitted for exploratory tympanoendoscopy for perilymphatic fistula detection. Twenty-five to 100 mg sodium fluorescein 10%, diluted with cerebrospinal fluid, was administered by lumbar puncture 2.5 to 23.5 hours before tympanoendoscopy. The oval and round window niches were microscopically and endoscopically observed with white and blue light, using specific filters. RESULTS: In two patients (7%), obvious fluorescence was detected behind the round window membrane with blue light. Direct observation of perilymph in stapedectomy and in semicircular canal fistula revealed no staining. Neurological complications of intrathecal fluorescein, as reported by other authors, were not observed. CONCLUSIONS: Probably because of a different patency of the cochlear aqueduct, intrathecal fluorescein for intraoperative detection of perilymphatic fistula resulted in a significant perilymph staining in only a few patients. Considering the possible complications of this method, we would not recommend it for routine evaluation of perilymphatic fistula.