Effects of perilymphatic pressure, sodium nitroprusside, and bupivacaine on cochlear fluid pH of guinea pigs.
CONCLUSIONS
Hydrostatic positive pressure and vasoconstrictor acidified the cochlear fluids, whereas the vasodilator made the fluids alkaline. CBF might play a role in regulating cochlea fluid pH.


OBJECTIVE
Cochlea fluid pH is highly dependent on the HCO3(-)/CO2 buffer system. Cochlear blood flow (CBF) supplies O2 and removes CO2. It is speculated that cochlear blood flow changes might affect the balance of the HCO3(-)/CO2 buffer system in the cochlea. It is known that the elevation of inner ear pressure decreases the CBF, and local application of vasodilating or vasoconstricting agents directly to the cochlea changes the CBF. The purpose of this study was to elucidate the effect of positive hydrostatic inner ear pressure and application of a vasodilator and vasoconstrictor of cochlear vessels on the pH of the endolymph and perilymph.


METHODS
The authors performed animal physiological experiments on 30 guinea pigs. Hydrostatic positive pressure was infused through a glass capillary tube inserted into the scala tympani of the basal turn. The vasodilator, nitric oxide donor (sodium nitroprusside; SNP), and the vasoconstrictor, bupivacaine, were placed topically onto the round window of the guinea pig cochlea. Endolymph pH (pHe) and endocochlear potential (EP) were monitored by double-barreled ion-selective microelectrodes in the second turn of the guinea pig cochlea. During the topical application study, scala vestibuli perilymph pH (pHv) was also measured simultaneously in the second turn.


RESULTS
The application of hydrostatic positive pressure caused a decrease in pHe and EP. Positive perilymphatic pressure caused the endolymph to become acidic pressure-dependently. Application of 3.0% SNP evoked an increase in both the pHe and pHv, following by a gradual recovery to baseline levels. On the other hand, 0.5% bupivacaine caused a decrease in both the pHe and pHv. The EP during topical application showed slight, non-significant changes.
a Department of Otolaryngology, Teikyo University Chiba Medical Center , Chiba, Japan.
Masaaki
M
Suzuki
a Department of Otolaryngology, Teikyo University Chiba Medical Center , Chiba, Japan.
Ryosuke
R
Kotani
D000779:Anesthetics, Local / Q000008:administration & dosage; D000818:Animals; D002045:Bupivacaine / Q000008:administration & dosage*; D003051:Cochlea / Q000187:drug effects / Q000502:physiology*; D003055:Cochlear Microphonic Potentials / Q000187:drug effects*; D005072:Evoked Potentials, Auditory / Q000187:drug effects; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D007761:Labyrinthine Fluids / Q000737:chemistry*; D020030:Nitric Oxide Donors / Q000008:administration & dosage; D009599:Nitroprusside / Q000008:administration & dosage*; D011312:Pressure; D012405:Round Window, Ear
D000779:Anesthetics, Local; D020030:Nitric Oxide Donors; D009599:Nitroprusside; D002045:Bupivacaine
Endolymph potential; cochlea fluids; pH