Intratympanic Dexamethasone, Nitroglycerin, Epinephrine on Cochlear Blood Flow in Guinea Pigs
Date Issued
2004
Date
2004
Author(s)
Chiang, Rayleigh Ping-Ying
DOI
zh-TW
Abstract
Background
Many kinds of inner ear diseases with suddenly occurred synptoms, either originating from cochlea or vestibule, were considered to be related to the impairment of the blood circulation. Sudden deafness is defined as idiopathic, sudden-onset sensorineural hearing loss. Traditional treatment for sudden deafness is by systemic administrated high dose steroid. There is, however, a new way to deliver the steroids through the “intratympanic” route to avoid possible side effects with traditional treatment and to achieve higher inner ear concentration of medicine.
The anti-inflammatory effects of steroids have been well accepted. However, the influence of steroids on blood circulation, more specifically, the cochlear microcirculation, is controversial. The main goal of this study is to determine if intratympanic delivered dexamethasone (DEX) affect the cochlear blood flow.
In addition, we use two drugs with clinically prompt and prominent vascular effects, i.e. nitroglycerin (NTG) and epinephrine (EPI). Reviewing the literatures, many authors considered the blood circulation effects of steroids, either promoting or reducing, are through modulating nitric oxide synthase(NOS) and the production of nitric oxide(NO). So we intratympanically administrate the NO donor, NTG, to see if the cochlear blood flow affected.
During middle ear surgery, epinephrine would come around round window membrane, either with epinephrine-containing anesthetics incidentally or with epinephrine-soaked cotton pledgets for hemostasis. We use the same animal model to see the effects of intratympanic epinephrine on the cochlear blood flow.
Methods
White Hartly guinea pigs with good Preyer’s reflex were used. After anesthesia, tracheostomy was done. Then systemic BP and body temperature were monitored. Under surgical microscope, mastoidectomy was performed to expose the cochlea. We applied dexamethasone, epinephrine, nitroglycerin or normal saline (as control) separately on to and around the round window membrane in this experiment. Laser Doppler flowmeter was used for CoBF measurement. The first 20 minutes was as the baseline, followed by 0.5 to 2 hours’ recording after medications.
Results
Valid data were from 45 guinea pigs. In dexamethasone group, CoBF increased significantly in 1 of 23 animals(42.9%), decreased in 4(17.39%) and showed no significant change in 18(78.26%). In NTG group, CoBF increased significantly in 5(62.5%) animals. In epinephrine group, CoBF decreased significantly in 7(77.78%) animals. In control group, CoBF didn’t change significantly in all 5 animals.
Conclusions
In this study, the effects of dexamethasone on CoBF were variable and not significant. There were, however, evidences to show that the glucocorticosteroid receptors do exist in the cochlea, which means that physiologically dexamethasone could excert some effect in the cochlea but not through the change of blood flow. The vaso-dilatational effect of the NO donor, NTG, on CoBF make us to infer that the NO-cGMP pathway play an important role in the regulation of blood circulation of cochlea as in other organs. Epinephrine yielded more consistent vaso-constrictional effect in this study. We suggest that ear surgeons avoid epinephrine incidentally placed around the round window membrane to avoid some undesirable outcome.
Subjects
腎上腺素
dexamethasone
耳蝸血流量
硝化甘油
耳內投予
突發性耳聾
雷射都卜勒血流測定儀
epinephrine
nitroglycerin
sudden deafness
laser Doppler flowmeter
cochlear blood flow
intratympanic administration
Type
text
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