ISSN:
1434-4726
Keywords:
Inner ear
;
Guinea pig
;
Perilymph-blood barrier
;
Radiotracer clearance experiments
;
Cochlear efflux kinetics
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Since 1950 many animal radiotracer experiments have been performed to study inner ear kinetics. For the most part in these studies, radionuclides were applied systemically, following which a discontinuous probing of inner ear fluids or of inner ear tissues was done. Two techniques have been developed in the Section for Experimental Otorhinolaryngology of the University of Würzburg. These have been adapted to the direct and continuous measurements of inner ear efflux kinetics for several hour periods. For this purpose, only a tiny amount of radiotracer need be applied directly to the inner ear. Experiments were done on the anesthetized guinea pig as an animal model. In the first technique, a collimator-detector system is focused precisely on the cochlea, which had been quickly resealed after application of the radionuclide bolus via two small holes in the basal turn of the cochlea. The second technique makes use of a perilymph cycling system, whereby a small outer volume includes a microcuvette with a socalled artificial round window. By this latter cycling technique, perilymph clearance kinetics of all kinds of radiotracers — with the exception of tritium labelled ones — can be measured. Calculations from clearance kinetics show that quite small particles with particle weights up to 100, such as the chlorine anion and the potassium cation, as well as urea, glycerol, pyruvate, and lactate, exhibit perilymphatic half-lives varying from 45 to 60 min. These half-live data are plausible in regard to cochlear blood flow measured previously via an independent technique developed by Angelborg et al. For particle weights distinctly beyond 100, half-lives increased gradually according to the operation of a perilymph-blood barrier. For a few tracers such as theophylline, nicotinamideadenine-dinucleotide, urografin, and biligrafin, individual effects are superimposed, giving rise to rather fast kinetics. In contrast, the ototoxic drugs ethacrynic acid and tobramycin exhibit a certain retardation in their clearance kinetics. Very small non-polar gaseous particles such as hydrogen and xenon show extremely short perilymphatic/cochlear half-lives. The half-life of hydrogen is about 4 min which accounts for a maximum clearance consistent with total cochlear blood flow.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00454128
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