Effect of adrenaline on transmesothelial resistance of isolated sheep pleura

Can pharmacologic agents speed the rate of resorption of pleural fluid?

PURPOSE OF REVIEW

Pleural effusion is a common clinical problem resulting from a wide range of diseases. Treatment options include targeting the primary cause or, in persistent cases, invasive removal of the excess fluid from the pleural cavity. In this review, we summarize the experimental data concerning pharmacological agents that influence pleural fluid resorption and examine their potential as a novel noninvasive treatment strategy.

RECENT FINDINGS

Recently published evidence indicates that adrenergic agents and corticosteroids can increase pleural fluid clearance from the cavity. On the contrary, paracetamol and certain nonsteroid anti-inflammatory drugs can impede fluid outflow. These concepts are based on data extracted by in-vivo studies using provoked hydrothoraces in rabbits and mice, as well as by ex-vivo electrophysiological experiments using sheep and human pleural tissue.

SUMMARY

In conclusion, the available experimental data indicate that certain pharmacological agents may impact fluid resorption, thus affecting pleural fluid accumulation and the rate of pleural effusion resolution.

Tight junction physiology of pleural mesothelium

Pleura consists of visceral and parietal cell layers, producing a fluid, which is necessary for lubrication of the pleural space. Function of both mesothelial cell layers is necessary for the regulation of a constant pleural fluid volume and composition to facilitate lung movement during breathing. Recent studies have demonstrated that pleural mesothelial cells show a distinct expression pattern of tight junction proteins which are known to ubiquitously determine paracellular permeability. Most tight junction proteins provide a sealing function to epithelia, but some have been shown to have a paracellular channel function or ambiguous properties. Here we provide an in-depth review of the current knowledge concerning specific functional contribution of these proteins determining transport and barrier function of pleural mesothelium.

Permeability of the arachnoid and pia mater. The role of ion channels in the leptomeningeal physiology

PURPOSE

The purpose of this paper is to study the ionic permeability of the leptomeninges related to the effect of ouabain (sodium-potassium-ATPase inhibitor) and amiloride (epithelial sodium channel (ENaC) inhibitor) on the tissue, as well as identify the presence of ion channels.

METHODS

Cranial leptomeningeal samples from 26 adult sheep were isolated. Electrophysiological measurements were performed with Ussing system and transmembrane resistance values (R(TM) in Ω*cm(2)) obtained over time. Experiments were conducted with the application of ouabain 10(-3) M or amiloride 10(-5) M at the arachnoidal and pial sides. Immunohistochemical studies of leptomeningeal tissue were prepared with alpha-1 sodium-potassium-ATPase (ATP1A1), beta-ENaC, and delta-ENaC subunit antibodies.

RESULTS

The application of ouabain at the arachnoidal side raised the transmembrane resistance statistically significantly and thus decreased its ionic permeability. The addition of ouabain at the pial side led also to a significant but less profound increment in transmembrane resistance. The addition of amiloride at the arachnoidal or pial side did not produce any statistical significant change in the R(TM) from controls (p > 0.05). Immunohistochemistry confirmed the presence of the ATP1A1 and beta- and delta-ENaC subunits at the leptomeninges.

CONCLUSIONS

In summary, leptomeningeal tissue possesses sodium-potassium-ATPase and ENaC ion channels. The application of ouabain alters the ionic permeability of the leptomeninges thus reflecting the role of sodium-potassium-ATPase. Amiloride application did not alter the ionic permeability of leptomeninges possibly due to localization of ENaC channels towards the subarachnoid space, away from the experimental application sites. The above properties of the tissue could potentially be related to cerebrospinal fluid turnover at this interface.

Dexamethasone decreases the transmesothelial electrical resistance of the parietal and visceral pleura

The effect of dexamethasone on the transmesothelial electrical resistance (R(TM)) of sheep pleura was investigated by Ussing chamber experiments. Our results show that dexamethasone decreases the R(TM) of sheep pleurae, in part by stimulation of glucocorticoid receptors. This finding may be of importance in regard to the faster resolution of corticosteroid-treated pleural effusions.

The contribution of ascorbic acid and dehydroascorbic acid to the protective role of pleura during inflammatory reactions

It is well-known that parapneumonic effusions lead to the formation of inflammatory exudates which contain an increasing amount of inflammatory cells, especially polymorphonuclear. At these pathological conditions characterized by oxidative stress, ascorbic acid (AA) plays an important role in quenching free radicals, so that it could protect neutrophils and mesothelial cells from oxidative damage. Besides that ascorbic acid and its metabolite dehydroascorbic acid (DHA) alters the sheep visceral and parietal pleura permeability. More specific ascorbic acid as well as dehydroascorbic acid decreases the permeability of pleura after addition on apical and basolateral side in both visceral and parietal pleurae. It seems that, AA and DHA have an opposite action upon pleura from that of the inflammatory mediators, like VEGF, which increases the permeability of pleura and causes mesothelial barrier dysfunction. The decrease of pleura permeability induced by AA and DHA suggest the hypothesis that AA and/or its metabolite DHA during inflammatory reactions not only protects mesothelial cells from oxidative damage, but also contributes to maintaining the mesothelial barrier function. Consequently, the inflammatory pleural fluid may be trapped in pleural space and the inflammation may be restricted, and have extension avoided.