Vasopressin entry into the inner ear fluids of the rat

The entry of arginine-vasopressin (AVP) and sucrose into cochlear endolymph, perilymph of scala vestibuli (PLV), perilymph of scala tympani (PLT), and cisternal cerebrospinal fluid (CSF) was studied, in anesthetized rats, after the administration into the cerebral lateral ventricle of a 10 microliter solution containing the radioactive tracers. Both tracers were detected in PLV, PLT, and CSF but not in endolymph. Monoexponential decay curves were calculated for PLV, PLT, and CSF, and for each tracer no difference was found between the regression lines calculated for the different fluids. These results indicate that (i) injection into the cerebral lateral ventricle is a useful tool to study the permeability of the cochlear epithelium to different solutes and (ii) no specific transport system exists for AVP across the cochlear epithelium, suggesting that AVP may exert its effect via the perilymphatic side of the stria vascularis.