Objective.-The purpose of this study was to investigate the effect of
furosemide on the endocochlear potential (EP) of Sprague-Dawley rats a
nd rats that lack albumin in their serum (Nagase analbuminemic rats [N
AR]). Design.-Group comparisons between analbuminemic rats and normal
Sprague-Dawley rats was carried out, with statistical evaluation using
the Student's t test.Setting.-Experiments were carried out in a sound
-attenuated booth in a research laboratory. Subjects.-Young adult Spra
gue-Dawley and analbuminemic rats (NAR) 50 to 80 days of age were used
as experimental animals. Interventions.-Subjects were anesthetized wi
th ketamine and xylazine. Furosemide, 35 mg/kg, was injected intraveno
usly in each of three groups: NAR rats, NAR rats pretreated with album
in and normal Sprague-Dawley rats. Main Outcome Measures.-Endocochlear
potential was measured via the round window membrane approach. Urine
samples were collected with a metabolic cage, and volumes were recorde
d. Results.-Sprague-Dawley rats had a very slight EP reduction followi
ng furosemide. The NAR rats, however, were found to have an extremely
large and rapid reduction of the EP one order of magnitude greater. Th
e NAR rats pretreated with albumin had a significantly smaller reducti
on of EP than NAR rats not receiving albumin. However, NAR rats pretre
ated with albumin had a significantly greater urine output than contro
l NAR rats. Conclusions.-These findings support the hypothesis that th
e access of furosemide to its site of ototoxic action in the cochlea d
epends on the quantity of unbound furosemide in the serum.