Experimental Endolymphatic Hydrops and Glycerol Electrophysiologic Study

Abstract

The object of the present study was to evaluate electrophysiologically the therapeutic effect of glycerol on the cochlear function of guinea pigs in which experimental hydrops had been surgically induced. Fifteen albino guinea pigs were used. Each animal was chronically implanted to follow the evolution of hearing. The experimental protocol considered 3 groups of guinea pigs (5 animals each). Group 1 received no drug treatment, while groups 2 and 3 were given glycerol orally at 0.75 and 0.50 g/kg of body weight once a day for 4 months. The audiograms of the animals treated with glycerol showed a statistically significant hearing improvement compared with the control group. Clinically, our results seem to support the view of those who favor the use of glycerol for the medical treatment of Meniere's disease at an early stage.

Hidropsia endolinfática experimental sob ação de inibidor da óxido nítrico sintase tipo II: avaliação com emissões otoacústicas e eletrococleografia

“…We have seen a progressive increase in electrophysiological thresholds in the control group in all the frequencies along the study period, initially in 1000 Hz already in the first week of postop, and in the remaining frequencies it started on the 8th week. Our findings are similar to those from other authors, confirming how adequate this animal is as an experimental model for endolymphatic hydrops 13,16,[23][24][25] . Thresholds were higher than preoperative measures, probably because we provided the acoustic stimuli through a head phone placed at 5cm from the ear while others used it at 1cm 22,24,26 or fit the phone to the external auditory canal 13 .…”

“…In this model there is an increase in endolymph pressure in comparison to the perilymph after the 2nd week 26 which may cause hearing loss induced by the mechanical action or by cell lesion. The use of diuretics, such as glycerol 25 , is capable of reducing electrophysiological thresholds increase, but it also does not prevent the disease onset, suggesting that the increase in endolymphatic pressure does play a role, but it is not the only factor involved. In order to reinforce this aspect, studies that promote the increase in endolymphatic pressure through a catheter positioned within the endolymphatic duct, assessing the endolymphatic pressure factor alone caused hearing loss, initially on the high frequencies, and later on reaching the lower frequencies.…”

A possible mechanism of the formation of endolymphatic hydrops and its associated inner ear disorders

“…Histologically, an intake of glycerol is well known to decrease EH [ 144]. Although there is some discrepancies in the effect of glycerol intake to the AP threshold of hydropic ears [145,146], cases with apparent improvement of AP threshold were reported [7,8,147]. In the experiment done by Takeda, one of the present authors, an intravenous injection of glycerol produced the improvement of the click-evoked AP threshold in 3 of 6 ears with experimentally-induced hydrops [7].…”

Modulation of hearing function following the downgrading or upgrading of endolymphatic hydrops in Meniere’s disease patients with endolymphatic duct blockage

“…A dehydration test via an osmotic diuretic to abruptly diminish hydrops is usually used to observe temporary reversal of hearing loss in MD [33][34][35][36][37]. Diuretic-induced endolymphatic dehydration has been radiologically observed in humans [38], with considerable evidence confirming that glycerol-induced endolymphatic volume load reduction occurs in animals [39][40][41][42]. In addition, the reduction of endolymphatic fluids resulting in hearing improvement has been described upon surgical observation; in cases where there was a flow of endolymph following drainage, an improvement in hearing at the low-pitched tone was observed, while in cases where there was no flow of endolymph, no improvement in hearing occurred [43].…”