Oral Administration Of Glycerol Research Articles

Optical clearing of living brains with MAGICAL to extend i nvivo imaging.

SummaryTo understand brain functions, it is important to observe directly how multiple neural circuits are performing in living brains. However, due to tissue opaqueness, observable depth and spatiotemporal resolution are severely degraded in vivo. Here, we propose an optical brain clearing method for in vivo fluorescence microscopy, termed MAGICAL (magical additive glycerol improves clear alive luminance). MAGICAL enabled two-photon microscopy to capture vivid images with fast speed, at cortical layer V and hippocampal CA1 in vivo. Moreover, MAGICAL promoted conventional confocal microscopy to visualize finer neuronal structures including synaptic boutons and spines in unprecedented deep regions, without intensive illumination leading to phototoxic effects. Fluorescence emission spectrum transmissive analysis showed that MAGICAL improved in vivo transmittance of shorter wavelength light, which is vulnerable to optical scattering, thus unsuited for in vivo microscopy. These results suggest that MAGICAL would transparentize living brains via scattering reduction.

Role of Aquaporin-3 in Intestinal Injury Induced by Sepsis.

Aquaporin-3 (AQP3) is expressed in various parts of the intestine, where it regulates the proliferation and migration of intestinal epithelial cells and the transport of glycerol and hydrogen peroxide. Our study aimed to investigate the effect on the expression of AQP3 of intestinal injury in septic mice and whether oral administration of glycerol can reduce intestinal epithelial injury and barrier disorder by acting as a partial substitute for the function of AQP3. We established a sepsis model by cecal ligation and perforation (CLP) in mice. Sepsis induced intestinal injury, as demonstrated by the disordered destruction of the morphology of the intestinal mucosa, time-dependent increases in Chiu's score (p < 0.05), significantly increased (p < 0.05) plasma concentrations of determination of the levels of diamine oxidase (DAO) and intestinal fatty acid-binding protein 2 (FABP2), and time-dependent downregulation of the expression of AQP3 and occluding (p < 0.05). While the administration of oral glycerol partially ameliorated the sepsis-induced injury of the intestinal mucosa, as shown by the partial recovery of the morphological structure, with decreased Chiu's score, decreased plasma concentrations of DAO and intestinal-type FABP2, upregulated expression of occludin and decreased mortality rate (Sepsis vs. Sepsis + Glycerol, p < 0.05). The results showed that the expression levels of AQP3 and occludin were downregulated after septic intestinal injury, while treatment with glycerol, which acts as a substitute for AQP3, partly ameliorated intestinal injury and improved the survival rate. This preliminary experiment suggests that AQP3 may protect the intestinal tract against the effects of sepsis.

Effect of glycerol test on audiovestibular tests in patients with Meniere’s disease

This stud to explore the effect of glycerol on audiovestibular tests in patients with Meniere’s disease (MD) and to reflect different pathologic states of endolymphatic hydrops (EH) in the inner ear and compare the results of glycerol on these results. SubjectsThirty patients and 15 normal volunteers. MethodsEach subject of this study underwent pure tone audiometry testing, evoked vestibular evoked myogenic potential (VEMP) and Vidionystagmography (VNG) before G1 and 2h after glycerol G2 administration (1.3g/kg). ResultsAffected ears were 32 and unaffected ears were 28. The affected ears had higher hearing and SRT thresholds when compared to the unaffected ears and control group. VEMPs of the affected ears were normal in six ears (18.75%), absent in four ears (12.5%) and augmented amplitude in 22 (68.75%), their VNG results showed peripheral vestibular disorder. After oral administration of glycerol, the previous test battery was repeated and it’s result on PTA showed that 53.13% (17/32) of affected ears had positive glycerol test mainly in stage II and III. Ten of the 32 affected ears (31.26%) showed improvement of VEMPs after glycerol administration. Also, two (7.8%) of the unaffected ears showed positive glycerol. Latency of the VEMP had no significant changes after glycerol administration and there was no statistical correlation between the results of G-PTA and G-VEMP. There was statistical significant improvement of the slow peak velocity of caloric test in patient’s affected ears and insignificant improvement in control group and in unaffected ears after glycerol administration.

Ovulation rate, prolificacy and pregnancy rate in goats treated with oral glycerol

This study tested whether the oral administration of glycerol at the time of progestin removal and in the first 6 days of the estrous cycle increased the ovulation rate, prolificacy, and pregnancy rate in goats. Intravaginal sponges impregnated with fluorogestone acetate were inserted into 129 goats for 12 days; upon sponge removal, goats were randomly assigned to one of the two following treatment groups: the glycerol group (n = 65), which received an oral drench of 100 mL of glycerol upon sponge removal and was repeated on days 0, 2, 4, and 6 following estrus (estrus = day 0), and the control group (n = 64), which did not receive glycerol. The goats in estrus were mated, and their ovulation rate was determined by ultrasonography between days 8 and 12 of the estrous cycle. Pregnancy was diagnosed by ultrasonography on day 40, and the prolificacy was determined at birth. In 6 goats treated with glycerol and 5 controls, their insulin concentrations at 0, 2, 4, 8, and 12 h after the glycerol drench were determined by radioimmunoassay. The proportion of goats with multiple ovulations (glycerol = 71 vs control = 64) and the proportion of goats with multiple births (glycerol = 52 vs control = 56) were similar (P &gt; 0.05) between treatments. Likewise, the pregnancy rate was similar (P &gt; 0.05) between treatments (glycerol = 88 vs control = 85%). The insulin concentrations tended to be higher in goats treated with glycerol (P = 0.08). In conclusion, an oral drench of 100 mL of glycerol at the time of progestin withdrawal and in the first 6 days of the estrous cycle did not increase the ovulation rate, prolificacy, or pregnancy rate in goats.

Investigation of glycemia recovery with oral administration of glycerol, pyruvate, and l-lactate during long-term, insulin-induced hypoglycemia

Aim The acute effect of oral administration of isolated or combined glycerol, pyruvate, and l-lactate on glycemia recovery (GR) during long-term, insulin-induced hypoglycemia (IIH) was compared. Methods Glycemia of 24 h-fasted rats that received intraperitoneal injection (1.0 U/kg) of regular insulin (IIH group) or saline (COG group) and, 15, 150, or 165 min later, oral saline (control IIH), glycerol (100 mg/kg), pyruvate (100 mg/kg), l-lactate (100 mg/kg), or combined glycerol+pyruvate+ l-lactate (each 33.3 or 100 mg/kg) was compared. In addition, for comparative purposes, a group that received glucose (100 mg/kg) was included. Glycemia was measured 180 min after insulin or saline injection. To investigate the participation of the hepatic availability of gluconeogenic substrates to GR, livers from IIH and COG rats that received physiological or supraphysiological concentrations of isolated or combined glycerol, pyruvate, and l-lactate were compared. Liver experiments were done 180 min after insulin or saline injection. Results Oral glycerol, pyruvate, and l-lactate (isolated or combined) or glucose promoted GR. Moreover, the best GR was obtained with combined glycerol+pyruvate+ l-lactate (100 mg/kg). In agreement, livers that received supraphysiological concentrations of glycerol, pyruvate, and l-lactate (isolated or combined) showed higher glucose release than livers that received physiological concentrations of these substances (isolated or combined). Conclusion The best GR obtained with combined administration of glycerol, pyruvate, and l-lactate (100 mg/kg) during long-term IIH was a consequence of the higher liver availability of these substances associated with a maintained liver ability to produce glucose from gluconeogenic substrates.

Severe glycerol intoxication after Menière's disease diagnostic – case report and overview of kinetic data

Objective. Despite the fact that glycerol is well known as a nontoxic substance, intoxication with this tertiary alcohol is possible. We report on a 72-year-old male who was referred to the Department of Neurology with progressive neurological symptoms that had developed 4 h prior to admission. Temporally associated was the so-called glycerol test or Klockhoff test, which was performed for the diagnosis of suspected Menière's disease. The test procedure starts with oral administration of glycerol, the maximal dose should not exceed 1.5 g/kg of body weight. Methods. Because of an apparently pathologically highly elevated serum concentration of triglycerides (3,465 mg/dL) measured 10 h after glycerol administration, the suspicion of an overdose of glycerol rose. During the following day, the glycerol serum concentration was analyzed at three different times. Results. Based on these measurements, we determined pharmacokinetic parameters and estimated the initially ingested amount of glycerol of about 3.88–3.95 g/kg body weight. Conclusion. We conclude that an accidental overdose of glycerol must have occurred during the glycerol test to the patient.

Characterization of response of gut GLI to fat ingestion in dogs.

Previous study from our laboratory demonstrated that an increased release of gut glucagon-like immunoreactivity (GLI) following triglyceride digestion was not observed in pancreatectomized dogs. Therefore, in order to clarify the response of gut GLI to triglyceride ingestion, experimental study was carried out in normal and pancreatectomized dogs. When butter was administered to pancreatectomized dogs in combination with pancreatic enzymes, plasma glucagon (IRG) measured by specific antiserum did not change significantly but plasma triglyceride as well as plasma total immunoreactive glucagon (total IRG) measured by nonspecific antiserum increased. Oral administration of glycerol induced no significant increase in plasma IRG but elicited a moderate increase of plasma total IRG. Gastric instillation of palmitic acid induced a remarkable rise of plasma total IRG in normal dogs, whereas plasma IRG did not reveal any changes. Oral administration of triglyceride of medium chain fatty acid, tricaprylin, did not promote any rise of plasma IRG but a slight increase of plasma total IRG. From the present experiment, it is concluded that hydrolysis of triglyceride and its metabolites are important in the release of gut GLI following fat ingestion. Among its metabolites, long chain fatty acid and glycerol promote the GLI secretion, whereas medium chain fatty acid does not.

Gluconeogenesis and ketogenesis in perfused liver of rats submitted to short‐term insulin‐induced hypoglycaemia

Gluconeogenesis and ketogenesis of in situ rat perfused liver submitted to short-term insulin-induced hypoglycaemia (IIH) were investigated. For this purpose, 24-h fasted rats that received intraperitoneal (ip) regular insulin (1.0 U kg(-1)) or saline were compared. The studies were performed 30 min after insulin (IIH group) or saline (COG group) injection. For gluconeogenesis studies, livers from the IIH and COG groups were perfused with increasing concentrations (from basal blood concentrations until saturating concentration) of glycerol, L-lactate (Lac) or pyruvate (Pyr). Livers of the IIH group showed maintained efficiency to produce glucose from glycerol and higher efficiency to produce glucose from Lac and Pyr. In agreement with these results the oral administration of glycerol (100 mg kg(-1)), Lac (100 mg kg(-1)), Pyr (100 mg kg(-1)) or glycerol (100 mg kg(-1)) + Lac (100 mg kg(-1)) + Pyr (100 mg kg(-1)) promoted glycaemia recovery. It can be inferred that the increased portal availability of Lac, Pyr and glycerol could help glycaemia recovery by a mechanism mediated, partly at least, by a maintained (glycerol) or increased (Lac and Pyr) hepatic efficiency to produce glucose. Moreover, in spite of the fact that insulin inhibits ketogenesis, the capacity of the liver to produce ketone bodies from octanoate during IIH was maintained.

Glycerol pure tone audiometry and glycerol vestibular evoked myogenic potential: representing specific status of endolymphatic hydrops in the inner ear

This prospective study attempts to explore the effect of glycerol on vestibular evoked myogenic potential (VEMP) in patients with definite unilateral Meniere's disease (MD) and to investigate whether the test reflects different pathologic states of endolymphatic hydrops (EH) in the inner ear by comparing the results of glycerol pure tone audiometry (PTA). Twenty-eight patients with definite unilateral MD were studied. As a control group, 11 patients with vestibular neuritis were selected. Sixteen ears of normal volunteers were enrolled to acquire normal range of the test. Each MD patient underwent glycerol testing measure with both conventional PTA and VEMP testing. Eleven vestibular neuritis patients also underwent glycerol-VEMP testing. The difference ratio was adopted to compare the changes in p1-n1 amplitude and latency of VEMP after the administration of glycerol (1.3 g/kg). Significant changes in the VEMP wave after the glycerol loading were seen in amplitude, but not in latency with MD patients. On the affected side, the amplitude of the p1-n1 biphasic wave significantly increased in 11 of 28 (39.3%) ears and decreased in 2 (7.1%) ears. On the unaffected side, 5 (17.9%) ears showed significant increase in amplitude. Significant changes in PTA were noted after administration of glycerol in 14 of 28 (50%) patients with MD. However, there was no statistically significant correlation between the test results. Glycerol administration had no significant effect on VEMP in patients with vestibular neuritis. The amplitude of VEMP in some patients with MD was increased, but the latency was not influenced by oral administration of glycerol. The severity of EH appears to vary in different parts of the inner ear. Glycerol-VEMP test results in patients with vestibular neuritis suggest that the VEMP reflects potential abnormality in the sacculocollic pathway, while glycerol-VEMP identifies the existence of EH in the saccule. VEMP and PTA after glycerol administration provide potential status of MD.

Impaired enterocyte proliferation in aquaporin-3 deficiency in mouse models of colitis

Background/Aims:Recent evidence has implicated the involvement of aquaporins (AQPs) in cellular functions that are unrelated to transepithelial water transport. Although AQPs are expressed in the gastrointestinal tract, their importance has...

Defective glycerol metabolism in aquaporin 9 (AQP9) knockout mice

Aquaporin-9 (AQP9) is an aquaglyceroporin membrane channel shown biophysically to conduct water, glycerol, and other small solutes. Because the physiological role/s of AQP9 remain undefined and the expression sites of AQP9 remain incomplete and conflicting, we generated AQP9 knockout mice. In the absence of physiological stress, knockout mice did not display any visible behavioral or severe physical abnormalities. Immunohistochemical analyses using multiple antibodies revealed AQP9 specific labeling in hepatocytes, epididymis, vas deferens, and in epidermis of wild type mice, but a complete absence of labeling in AQP9(-/-) mice. In brain, no detectable labeling was observed. Compared with control mice, plasma levels of glycerol and triglycerides were markedly increased in AQP9(-/-) mice, whereas glucose, urea, free fatty acids, alkaline phosphatase, and cholesterol were not significantly different. Oral administration of glycerol to fasted mice resulted in an acute rise in blood glucose levels in both AQP9(-/-) and AQP9(+/-) mice, revealing no defect in utilization of exogenous glycerol as a gluconeogenic substrate and indicating a high gluconeogenic capacity in nonhepatic organs. Obese Lepr(db)/Lepr(db) AQP9(-/-) and obese Lepr(db)/Lepr(db) AQP9(+/-) mice showed similar body weight, whereas the glycerol levels in obese Lepr(db)/Lepr(db) AQP9(-/-) mice were dramatically increased. Consistent with a role of AQP9 in hepatic uptake of glycerol, blood glucose levels were significantly reduced in Lepr(db)/Lepr(db) AQP9(-/-) mice compared with Lepr(db)/Lepr(db) AQP9(+/-) in response to 3 h of fasting. Thus, AQP9 is important for hepatic glycerol metabolism and may play a role in glycerol and glucose metabolism in diabetes mellitus.

グリセロール経口投与による乳牛の血中成分の変化とケトーシスの治療効果

Investigations of blood-component changes and therapeutic effects produced in cows with subclinical and clinical ketosis by orally administered glycerol showed that glucose and free glycerol concentrations increased at 0.5 hrs after single oral administrations of 500ml, 1, 000ml, and 2, 000ml and that, from 0.5 to 6 hrs and at 24 hrs after administration, these levels were significantly higher than they had been before administration. Serum concentrations of β hydroxybutyric acid decreased from 4 to 6 hrs and at 24 hrs after single glycerol administration. One or two days after initial administration, appetite and rumen movement were restored in 10 of 20 ketotic cows kept on a daily dose of 1, 000ml of glycerol for three days. Ketone bodies disappeared from the urine three days after initial administration. These findings suggest that oral administration of glycerol may have a therapeutic effect on ketosis.

Vestibular Evoked Myogenic Potentials in Ipsilateral Delayed Endolymphatic Hydrops

We recorded vestibular evoked myogenic potentials (VEMPs) in 12 patients diagnosed as having ipsilateral delayed endolymphatic hydrops (DEH). Seventy-five percent (9/12) of the patients showed decreased or absent VEMPs in the affected ears. Almost all patients had normal VEMPs in the unaffected ears. In addition, in 4 patients, VEMPs were recorded before and 3 h after oral glycerol administration (1.3 g/kg body weight). VEMPs improved after glycerol administration in 2 of the 3 patients whose VEMPs had been abnormal in the affected ears before glycerol administration. None of the 4 patients presented significant changes in VEMPs in the unaffected ears after glycerol administration. Improvement of VEMPs after glycerol administration confirmed the existence of endolymphatic hydrops in patients with ipsilateral DEH. In conclusion, VEMPs are useful to evaluate the function of otolith organs in patients with ipsilateral DEH, and the glycerol test using VEMPs may be useful to detect endolymphatic hydrops in ipsilateral DEH.

Vestibular evoked myogenic potentials in patients with contralateral delayed endolymphatic hydrops.

We studied vestibular evoked myogenic potentials (VEMPs) in nine patients with unilateral profound hearing loss followed by contralateral delayed hearing fluctuation and episodic vertigo. This condition has been called contralateral delayed endolymphatic hydrops. Five of nine ears with profound hearing loss (56%) showed an absence of VEMPs. One ear (11%) showed decreased responses, and three ears (33%) had normal responses. Of the ears with fluctuation of hearing, six (67%) showed an absence of responses, and three ears (33%) showed normal responses. In four patients we recorded VEMPs before and after oral administration of glycerol. Three hours after glycerol administration, two of four ears with fluctuating hearing loss showed the appearance of VEMPs although there was an absence of VEMPs before glycerol administration. These results suggested that saccular dysfunction could exist not only in the ears with profound hearing loss but also in ears with fluctuating hearing loss and that saccular endolymphatic hydrops could exist in the ears with fluctuating hearing loss. "Contralateral delayed endolymphatic hydrops" might be an appropriate term.

Glycerol affects vestibular evoked myogenic potentials in Meniere's disease

Objectives: to show that abnormal vestibular evoked myogenic potentials on the sternocleidomastoid muscle (SCM) in patients with unilateral Meniere's disease are caused by endolymphatic hydrops. Subjects: six normal volunteers and 17 patients with unilateral Meniere's disease were examined. Methods: click-evoked myogenic potentials were recorded with surface electrodes over each SCM. Responses evoked by clicks recorded after oral administration of glycerol (1.3 g/kg body weight) were compared with those recorded before administration. Results: the change rate of the p13–n23 amplitude was calculated. The mean+standard deviation (S.D.) of the change rate was 3.52+14.6% in normal subjects. On the unaffected side of patients the change rates were within the normal range (within the mean±2S.D.) in 13 patients, and three ears showed significant decrease. Only one ear showed significant increase. On the affected side, five ears showed significant increase of the amplitude while two ears showed significant decrease after oral administration of glycerol. Effects on evoked myogenic potentials were independent of those on pure tone hearing. Conclusion: vestibular evoked myogenic potentials in some patients with unilateral Meniere's disease were improved by oral administration of glycerol. This result suggests that abnormal vestibular evoked myogenic potentials in patients with unilateral Meniere's disease could result from endolymphatic hydrops.

Changes in otoacoustic emission during the glycerol test in the ears of patients with Meniere's disease

Monitoring of cochlear function is one proposed clinical application of otoacoustic emission (OAE). To determine the clinical utility of OAE in monitoring, we studied changes in OAE during the glycerol test used to diagnose endolymphatic hydrops. Transiently evoked OAE (TEOAE) and distortion product OAE (DPOAE) were measured before and 3 hours after oral administration of glycerol in 22 ears of patients with Meniere's disease. The positive result in the glycerol test was observed in 11 of 22 ears. TEOAE was recorded using a nonlinear click stimulus, and total echo power (TEP) of the whole response and filtered echo power (FEP) of its mid-frequency (1000-2000 Hz) component were used as TEOAE parameters. The growth functions of DPOAE were recorded at 3 F2 frequencies--1000, 1500, and 2000 Hz. Changes in the growth function were determined based on changes in 2 parameters--maximum level and detection threshold of DPOAE. When changes in these 4 parameters exceeded 2 standard deviations above mean test-retest variability determined from OAE data for 17 normal ears, they were considered significant. Significant changes indicating improved cochlear function in 4 OAE parameters or the appearance of OAE during the glycerol test were judged positive for OAE. Regardless of glycerol test results, positive findings were observed in both OAEs whenever a pure-tone threshold at 1000 or 2000 Hz improved. However, even in ears for which pure-tone thresholds at these frequencies did not improve, both OAEs frequently exhibited positive findings. In all ears with a positive result in the glycerol test, positive findings were observed in DPOAE, but not in TEOAE. Of the 2 parameters of TEOAE, FEP always exhibited a positive finding in ears with a positive TEP finding and FEP positivity was higher than that of TEP. In DPOAE, no cases showed a positive finding only at F2 = 2000 Hz, and DPOAE at F2 = 1000 Hz could not be detected in 4 ears due to high noise floor. Overall, positive findings were obtained in 14 ears (63.9%) for TEOAE and 20 ears (90.9%) for DPOAE. In only 1 ear were no positive findings observed in either OAE. The sensitivity of OAE measurement as a diagnostic test for endolymphatic hydrops was higher than that of pure-tone audiometry. Of the 2 OAEs, test sensitivity was much higher for DPOAE than for TEOAE. These results show that OAE measurement detects changes in cochlear function during the glycerol test more sensitively than pure-tone audiometry. They also suggest that FEP is a better indicator than TEP as a parameter of TEOAE, and that DPOAE measurement at F2 = 1000 and 1500 Hz is sufficient for practical clinical use. However, of the 2 OAEs, DPOAE was considered more appropriate than TEOAE for monitoring during the glycerol test because of its high sensitivity in detection of changes in cochlear function. In conclusion, clinical use of OAE, especially DPOAE, as a test complementary to pure-tone audiometry during the glycerol test is very useful and will improve the diagnosis of endolymphatic hydrops.

Glycerol-induced seizure: involvement of IL-1beta and glutamate.

It is widely accepted that interleukin-1beta (IL-1beta), a cytokine produced not only by cells of the immune system but also by cells of the central nervous system, modulates hippocampal function. Here we investigate the effect of a seizure-induced increase in hippocampal IL-1beta concentration on neurotransmitter release. We report that oral administration of glycerol evoked seizure activity in BALB/c mice. Associated with these convulsions was an induction of IL-1beta gene expression and a significant increase in cytokine protein in the hippocampus. Release of glutamate in synaptosomes prepared from hippocampi of these animals was reduced compared to control. These results are consistent with previous data suggesting a modulatory effect of IL-1beta on glutamate release in hippocampus.

Immunoreactivity for taurine in the cochlea: its abundance in supporting cells

Taurine is the second most abundant free amino acid in the brain where its osmoregulatory function is well established. Taurine-deprived kittens show retinal pathology leading to blindness. In the inner ear, taurine has been reported to be the most abundant free amino acid although its role in inner ear function is not known. Immunohistochemistry was employed here to investigate the localisation of taurine in normal cochleae of the guinea pig compared with two different conditions: experimentally induced endolymphatic hydrops and after oral administration of glycerol. In normal cochleae, by light microscopy, taurine-like immunoreaction was never observed in the sensory outer hair cells and appeared absent from the inner hair cells. In contrast taurine-like immunolabeling was found to be present in all supporting tissue with the striking exception of the tectorial membrane and the outer pillar cell which had no or little taurine immunoreactivity respectively. In early experimental endolymphatic hydrops, the distribution of taurine-like immunoreactivity appeared similar to that observed for normal cochleae. In long-term hydrops, degenerated outer hair cells were replaced by the swelling of the phalangeal process of the Deiters' cells which became highly immunoreactive to taurine. After glycerol administration, the tectorial membrane became more tightly bound to the apical surface of the sensory hair cells and distinctly immunoreactive to taurine. The localisation of taurine in the organ of Corti shown here is consistent with taurine being involved in the maintenance of osmotic equilibrium in the normal and perhaps also in the restructuration of the pathological organ of Corti.

Effect of Acute Glycerol Administration with or without a Mixed Meal in Humans

We explored the effects of oral glycerol administration (20 g) alone or in combination with a mixed meal on postprandial lipids, free fatty acids, high-density lipoprotein cholesterol and retinyl palmitate. We also tested the meal alone as a control. The metabolic behavior of 13C-labelled glycerol, mainly its incorporation into triglycerides and glucose, was also investigated. The tests were performed on 13 healthy subjects aged 20-56 years (mean 32.1 +/- 10.8). Glycerol administration alone induced a decrease in plasma free fatty acid levels. When glycerol was given with the meal, it was absorbed faster and postprandial triglyceride levels were higher compared to the meal alone (p < 0.05). An earlier and higher peak of retinyl palmitate was also observed when comparing the glycerol and mixed meal test to the mixed meal alone. No significant effect was observed on total, high-density and low-density lipoprotein cholesterol. These results suggest that the glycerol-induced increase in postprandial triglyceride levels is probably due to an increase in chylomicron synthesis and perhaps to the stimulation of intestinal glycerol kinase activity. 13C-labelled glycerol administration showed a more important glycerol incorporation in lipoproteins with a density range of < 1.006 during the test with glycerol alone as compared to the test with glycerol and a mixed meal, suggesting that the rate of glycerol incorporation into lipoproteins depends on the availability of other substrates.

Extratympanic electrocochleography during glycerol dehydration test in unilateral Ménière's diseases

Extratympanic electrocochleography and pure-tone audiometry were performed in unilateral Ménière's disease patients before and 1, 2 and 3 hours after oral administration of glycerol. The mean electrocochleographic response from 12 recordings at 80 dBnHL click stimuli was determined to obtain stable values. The electrocochleographic response during the glycerol dehydration test was compared with that in normal subjects (28 ears). A positive result on a pure-tone audiogram was determined by an improvement of at least 10 dB in two octave bands. In 25 involved ears with Ménière's disease, the action potential (AP) amplitudes gradually decreased during the test, but there were no significant differences. The summating potential (SP) amplitudes decreased during the test and there was a significant difference at 2 hours after administration. The negative SP/AP ratios were unchanged. The Ménière's disease patients were classified into two groups; one with a positive response on the audiogram and the other negative responses including deterioration. According to multiple comparison testing, there were significant differences in AP amplitudes and SP amplitudes between the positive group and normal controls at 2 and 3 hours after administration, and between the positive group and the negative group at 3 hours. Electrocochleographic changes in the positive audiogram group were significant. Then, the patients were classified into three groups by negative SP/AP ratio before administration. The first group consisted of negative ears whose negative SP/AP ratios were less than 0.36, which was the upper 95% confidence limit for 40 normal hearing ears, the second consisted of slightly positive ears (0.36 < or = negative SP/AP ratio < 0.40), the last consisted of severely positive ears whose ratios were more than 0.4, which was the upper 99% confidence limit. There was a significant difference for the SP amplitudes between the slightly positive group and normal controls at 2 hours after administration. Electrocochleographic changes in the slightly positive group with a negative SP/AP ratio were significant at this SP amplitude. In 18 normal ears with Ménière's disease, electrocochleographic changes showed no significant difference. However, the SP amplitudes in 3 ears and the negative SP/AP ratios in 4 ears decreased to less than 80% of the pre-administration value, although they had not fallen below that in the normal controls. These decreases indicate that some normal ears with Ménière's disease already had the distinctive features of involved ears. Whether the fluctuation in hearing will appear in the normal ears with decreasing SP amplitudes or negative SP/AP ratios, as in the involved ears, remains to be determined.