Isoprenaline-induced facilitation of the Eustachian tube opening

Functional study of mucus secretion of the eustachian tube in Guinea pigs

OBJECTIVES

Our aim was to verify neural regulation of submucous gland mucus secretions in the Eustachian tubes of guinea pigs.

STUDY DESIGN

Prospective animal study.

METHODS

Eustachian tubes harvested from 12 guinea pigs were used for this study. For real-time resolution of pure glandular secretion, we used a modified method of single-gland optical measurement. Secretory monitoring was undertaken after each preparation with phenylephrine, isoproterenol, forskolin, and substance P. To confirm the viability of each tissue, we examined glandular secretion after treatment with carbachol. Secretory effects of each agonist were evaluated by comparing with basal secretion using a Student's t test (p < 0.01).

RESULTS

The Ca-elevating agonists carbachol and substance P showed greater effects on submucous gland secretions of the Eustachian tube than the cyclic adenosine monophosphate (cAMP)-elevating agonists forskolin and isoproterenol. However, phenylephrine, although it belongs to the Ca-elevating agonist group, did not show any significant secretory effect.

CONCLUSION

The optical measurement method used in this study had the merit of real-time resolution of submucous glandular secretion. Submucous glandular secretion in the Eustachian tube was regulated by both Ca- and cAMP-elevating agonists, and Ca-elevating agonists seemed to be more potent than cAMP-elevating agonists except phenylephrine. Our results suggest that not only the autonomic nerve system but also the neuropeptides such as substance P are closely related to glandular secretion in the Eustachian tube, and beta-adrenergic receptors seem to be more related to submucous glandular secretion of the Eustachian tube in guinea pig than alpha-adrenergic receptors.

Therapeutic improvement of Eustachian tube function: a review

An impaired Eustachian tube is assumed to be an important factor in the pathogenesis of different middle ear diseases. Therefore, several investigators have studied different treatment strategies to improve Eustachian tube function. The aim of this review is to provide a comprehensive summary of the results of these studies on improvement of tubal function. The English language literature was searched systematically to identify all articles that described the effect of different interventions on Eustachian tube function. Although the results were not uniform throughout the different studies and despite several restrictions of the reviewed studies, the results of this review indicate that the function may be improved by medical intervention. However, it seems premature to recommend any of the interventions reviewed in this paper to improve function in humans. More studies, preferably randomized, placebo-controlled trials, should be conducted to assess the efficacy of different interventions.

Dosage regimens of intranasal aerosolized surfactant on otitis media with effusion in an animal model

OBJECTIVE

To determine optimal dosage regimens of intranasal metered dose aerosolized surfactant with and without other medications in the treatment of otitis media with effusion (OME).

STUDY DESIGN

Resolution of experimental OME in gerbils was determined based on otomicroscopy and tympanometry. Experimental intranasal drugs were: surfactant, surfactant with betamethasone, surfactant with phenylephrine, and a normal saline solution placebo. Medications were administered once or twice daily via a metered dose inhaler.

RESULTS

For twice-daily dosing, mean days to OME resolution were 8.5 for the aerosolized surfactant, 6.3 for the surfactant with betamethasone, 18.7 for the surfactant with phenylephrine, and 16 each for control and placebo. Resolution with the once-daily dosage was longer for all conditions. Results were comparable using tympanometry.

CONCLUSION

OME resolved faster than the natural course when treated with intranasal surfactant with and without steroids. Twice-daily dosing was statistically superior.

SIGNIFICANCE

This study reiterates the effectiveness of OME treatment with an aerosolized synthetic surfactant with and without steroids and establishes a superior twice-daily dosage schedule.

Drug-Induced Changes in Eustachian Tube Function

Many studies have shown that antihistamines and decongestants are of little use in the treatment of acute otitis media and otitis media with effusion, or in the prophylaxis of these disorders.1 However, because some drugs can improve otitis media with effusion (glycocorticosteroids)2–4 and some can impair the opening function of the eustachian tube (atropine),5 it seems justified to continue studies of eustachian tube function and medication.

Influence of surface condition of mucosa of eustachian tube on tubal compliance

To clarify the influence of the mucosal condition of the eustachian tube (ET) upon its collapsibility, three experimental studies were performed by using the forced response test. First, by washout of the mucous blanket of ET, the tubal compliance index (TCI), the ratio of passive tubal resistances at two different airflow rates, significantly increased in all the 6 ETs of 5 cats, and all returned to the baseline within 50 min. Second, the TCIs significantly decreased in all the 7 ETs of 5 cats after application of Triton X (surfactant) into the ET washed out by saline. Third, the increased TCIs of a tubal model by application of saline significantly decreased after application of Triton X. These results seem to support our hypothesis that compliance of the ET, which means its collapsibility, may depend upon the mucosal condition as well as on the property of the cartilaginous framework of ET.

The effect of surfactant on eustachian tube function in a gerbil model of otitis media with effusion

The relationship of eustachian tube surfactant and otitis media with effusion on eustachian tube opening pressure was studied in a gerbil model. Injection of killed Streptococcus pneumoniae bacteria created a serous effusion that increased eustachian tube opening pressure. The introduction of exogenous surfactant to this system resulted in a dramatic decrease in eustachian tube opening pressure in both normal ears and those with effusion. Identifying means to increase surfactant in the eustachian tube could be beneficial in reducing persistent otitis media with effusion.

Surfactant and isoprenaline effect on eustachian tube opening in rats with acute otitis media

Purulent otitis media was induced in 12 middle ears of Sprague-Dawley rats by inoculation of pneumococci type 3. The pressure required to open the eustachian tube was recorded 4 days later and was found to be 3.05 +/- 0.10 kPa (mean +/- SEM), which was 1.08 +/- 0.15 kPa lower than the mean value obtained in a control group of healthy rats (P less than or equal to .001). We also measured the effects of pulmonary surfactant instilled into the middle ear as well as isoprenaline injected intravenously. The presence of surfactant further reduced the pressure opening level by 0.72 +/- 0.05 kPa; this reduction did not differ from that found in the control group (P greater than .8). Isoprenaline reduced the pressure opening level in the control group by 0.20 +/- 0.03 kPa (P less than or equal to .001), and no reduction was found in the rats with otitis media. Although the part played by surface tension-lowering factors in eustachian tube function is still uncertain, such factors apparently also exert an effect in the inflamed tube. However, isoprenaline, which is considered to act by the secretion of surface tension-lowering substances, did not facilitate opening of the eustachian tube in rats with acute otitis media.

Surfactant-like lamellar bodies in the mucosa of the human nose

Specimens from the epithelium on the lateral wall of the human nose were examined under the electron microscope using a lipid and carbohydrate retaining method. In many of the ciliated epithelial cells and in some of the cells in the mucosal glands we identified multilamellated granules. These structures resembled lamellar bodies as found in normal alveoles where they are known to represent surfactant. The effect of phospholipid and the upper respiratory system is unknown but the similarities of these granules suggest to us a surface active function as it seems to play a role for normal Eustachian tube function.

Effect of exogenous surfactant on eustachian tube function in the rat

Three solutions, surfactant prepared from pig lungs, a mixture of synthetic phospholipids, and saline solution, were instilled into the middle ears of rats. The middle ear pressure necessary to force the eustachian tube open was studied. Ten minutes after instillation of pulmonary surfactant there was a 0.58 +/- 0.10 kPa decrease in the pressure opening level (P less than .001). The reduction persisted throughout the 50-minute experiment. There was also a reduction 0.17 +/- 0.16 kPa in the pressure opening level (P less than .01) after the administration of the synthetic phospholipid mixture. This reduction was significantly less than the reduction produced by the pulmonary surfactant. No decrease in the pressure opening level was seen after the instillation of saline solution into the middle ear cavity. The fact that surfactants are demonstrable in the middle ear and eustachian tube, coupled with these findings of an effect on the tubal opening, suggests a physiologic role for surface tension-lowering substances in tubal function.

The effect of gestation on eustachian tube function in rats

Patulous Eustachian tube (tuba aperta) is a distressing condition for the patient with such symptoms as autophony and a sensation of fullness in the ear. One-third of women with the diagnosis are pregnant or taking oestrogens. To study whether opening of the Eustachian tube is facilitated during pregnancy, the tube opening function of 14 pregnant rats was compared with that of 14 non-pregnant controls. The middle ear air pressure at which the tube opened (the pressure opening level, Pol) was lower in pregnant rats than in controls; and the difference between Pol and the pressure during open tube (at continued air injection) was less in the pregnant rats. In two additional rats it was then demonstrated that instillation of a surface tension lowering substance in the middle ear caused similar pressure changes as occur during pregnancy. It is concluded that opening of the Eustachian tube in rats is facilitated in pregnancy, and it is suggested that this is due to a reduction in surface tension of the Eustachian tube secretion.

Effects of an anti-cholinergic on the function of patulous eustachian tube

Clinical diagnoses concerning patulous eustachian tube are often difficult to make. Also, no specific therapy for patulous tube has been established. Therefore, in this experiment, we attempted to design a method by which we could examine tubal function and make both diagnoses and therapeutic evaluations of patulous tube. The tube of an ear suffering from patulous tube tended to be easily opened by air insufflation in comparison to that of a normal ear. The intra-tubal treatment of patulous tube by atropine, an anti-cholinergic, alleviated both the impaired tubal function and complaints such as ear fullness and autophonia. The results suggest that topical administration with anti-cholinergics should be an effective treatment for patulous eustachian tube.

Secretory otitis media--a question of surface activity in the eustachian tube?

An improved thin-layer chromatographic assay for monitoring phospholipid ratio in mucus was used to study the respiratory system distribution of children with and without secretory otitis media. Phosphatidylcholine, phosphatidylethanolamine and sphingomyelin abound, while only traces of other phospholipids are found. Analyses show more sphingomyelin and less phosphatidylcholine in the Eustachian tube and nose than in the lung, while phosphatidylethanolamine has about the same distribution. The phosphatidylcholine/sphingomyelin ratio is significantly less in Eustachian tube mucus from children with secretory otitis media compared with otologically healthy children, which indicates a different secretory pattern of the cells in the Eustachian tube of these children. The distribution of phospholipids in middle ear secretion is different from the distribution obtained from the Eustachian tube in children with secretory otitis media thus verifying a clearance 'blocking' of the tube caused by the disease.

The influence of pregnancy on the eustachian tube function in rats

Textbooks of otorhinolaryngology usually report that one-third of women diagnosed for patulous Eustachian tube (tuba aperta) are pregnant or on estrogenic therapy. To investigate whether the opening of the Eustachian tube (ET) can be facilitated experimentally during pregnancy, the ET opening function of 14 pregnant rats was compared with that of 14 nonpregnant controls. The air pressure at which the ET opened (the pressure opening level, Pol) when air is injected into the middle ear, and the pressures maintaining open ET during continued air injection were measured. The Pol was lower in the pregnant rats, whereas there was no difference in pressures between the two groups during open ET. The differences between Pol and the pressures during open ET were smaller in the pregnant rats than in the controls. It was furthermore demonstrated in 2 rats that, after instillation of a surface tension lowering substance in the middle ear, the Pol was reduced markedly, whereas the effect on the pressure during open ET was less pronounced. It is concluded that pregnancy facilitates opening of the ET in rats and it is suggested that it is done by reducing the surface tension of the ET secretion.

Sympathetic stimulation of amylase secretion during a parasympathetic background activity in the rat parotid gland

The amylase secretion in vivo was examined in the rat parotid gland. A comparison was made between individual stimulation of sympathetic and parasympathetic nerves and simultaneous activation of both nerves. When sympathetic stimulation was superimposed on a parasympathetic background activity, amylase secretion was elicited at a frequency far below the threshold for secretion of fluid, and increased in a frequency-dependent way. This augmented amylase secretion, seen when the two nerves were activated at the same time, gave an amylase output which far exceeded the sum obtained at individual nerve stimulation. The sympathetic amylase secretion obtained in a background of parasympathetic activity seemed to be dependent entirely on beta 1-adrenoceptors. When high sympathetic stimulation frequency (3-10 Hz) was used a reduction in salivary flow was seen, which was accompanied by a reduced amylase output. This effect was counteracted by alpha-adrenoceptor blockade. Isoprenaline, injected intravenously during an ongoing parasympathetic activity, was found to evoke an augmented amylase secretion in a similar way as sympathetic nerve stimulation.