Biochemical differences between perilymph, cerebrospinal fluid and blood plasma in the guinea pig

Seven selected biochemical substances were systematically analyzed in perilymph (PL), cerebrospinal fluid (CSF) and blood plasma or serum of anesthetized guinea pigs in order to compare the composition of these fluids with regard to the origin and biochemical nature of PL. Compositional differences between the fluids were expressed by PL/CSF and PL/plasma concentration ratios of the chemical components measured. Contrary to the prevailing notion, the results suggest that the specific biochemical composition of PL corresponds neither to that of CSF nor to that of a simple ultrafiltrate of blood plasma. Furthermore, except for the total protein concentration, no significant differences were found in the composition of PL between the scala tympani and scala vestibuli.