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

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 acutely accelerates pleural fluid absorption in mice hydrothoraces

This study assessed the effect of corticosteroid treatment in the clearance of hydrothoraces in mice. Twenty-four C57BL/6 mice were divided into four groups and were injected intrapleurally with 500 microL sterilized PBS-BSA 1% to create isosmotic hydrothoraces. Two groups served as control and two groups were treated with dexamethasone. The control groups received intraperitoneally PBS, while the corticosteroid treatment groups received dexamethasone (1 mg/kg), both 5 min after the induction of hydrothorax. Control and treated animals were sacrificed 2 and 4 h after the induction of hydrothorax, and pleural fluid volume was measured. The pleural fluid volume 2 and 4 h after the induction of hydrothoraces was significantly lower in the dexamethasone-treated group compared to the untreated group. The rate of pleural fluid absorption 2 and 4 h after the induction of hydrothoraces was significantly higher in the dexamethasone-treated groups. The present study demonstrated that dexamethasone accelerates pleural fluid absorption in induced isosmotic hydrothoraces in mice. This newly reported property of dexamethasone may partly account for the clinical observation of faster resolution of pleural effusions when corticosteroids are administered in patients with pleural effusions of certain etiologies.