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1.  Physiology of pericardial fluid production and drainage 
The pericardium is one of the serosal cavities of the mammals. It consists of two anatomical structures closely connected, an external sac of fibrous connective tissue, that is called fibrous pericardium and an internal that is called serous pericardium coating the internal surface of the fibrous pericardium (parietal layer) and the heart (visceral layer) forming the pericardial space. Between these two layers a small amount of fluid exists that is called pericardial fluid. The pericardial fluid is a product of ultrafiltration and is considered to be drained by lymphatic capillary bed mainly. Under normal conditions it provides lubrication during heart beating while the mesothelial cells that line the membrane may also have a role in the absorption of the pericardial fluid along with the pericardial lymphatics. Here, we provide a review of the the current literature regarding the physiology of the pericardial space and the regulation of pericardial fluid turnover and highlight the areas that need to be further investigated.
PMCID: PMC4364155  PMID: 25852564
mesothelium; pericardiac fluid turnover; pericardium; serosal membranes; transmembrane transport
2.  Long-term exposure to muscarinic agonists decreases expression of contractile proteins and responsiveness of rabbit tracheal smooth muscle cells 
Chronic airway diseases, like asthma or COPD, are characterized by excessive acetylcholine release and airway remodeling. The aim of this study was to investigate the long-term effect of muscarinic agonists on the phenotype and proliferation of rabbit tracheal airway smooth muscle cells (ASMCs).
ASMCs were serum starved before treatment with muscarinic agonists. Cell phenotype was studied by optical microscopy and indirect immunofluorescence, using smooth muscle α-actin, desmin and SM-Myosin Heavy Chain (SM-MHC) antibodies. [N-methyl-3H]scopolamine binding studies were performed in order to assess M3 muscarinic receptor expression on isolated cell membranes. Contractility studies were performed on isolated ASMCs treated with muscarinic agonists. Proliferation was estimated using methyl-[3H]thymidine incorporation, MTT or cell counting methods. Involvement of PI3K and MAPK signalling pathways was studied by cell incubation with the pathway inhibitors LY294002 and PD98059 respectively.
Prolonged culture of ASMCs with acetylcholine, carbachol or FBS, reduced the expression of α-actin, desmin and SM-MHC compared to cells cultured in serum free medium. Treatment of ASMCs with muscarinic agonists for 3-15 days decreased muscarinic receptor expression and their responsiveness to muscarinic stimulation. Acetylcholine and carbachol induced DNA synthesis and increased cell number, of ASMCs that had acquired a contractile phenotype by 7 day serum starvation. This effect was mediated via a PI3K and MAPK dependent mechanism.
Prolonged exposure of rabbit ASMCs to muscarinic agonists decreases the expression of smooth muscle specific marker proteins, down-regulates muscarinic receptors and decreases ASMC contractile responsiveness. Muscarinic agonists are mitogenic, via the PI3K and MAPK signalling pathways.
PMCID: PMC3995846  PMID: 24607024
Airway smooth muscle; Acetylcholine; Carbachol; Phenotype; Proliferation
4.  Endothelial Progenitor Cells in the Pathogenesis of Idiopathic Pulmonary Fibrosis: An Evolving Concept 
PLoS ONE  2013;8(1):e53658.
Idiopathic pulmonary fibrosis (IPF) has been associated with abnormal vascular remodeling. Bone marrow derived endothelial progenitor cells (EPCs) are considered to possess lung tissue repair and vascular remodeling properties.
The study aimed to assess early EPCs levels and EPCs endogenous vascular endothelial growth factor (VEGF) expression in IPF. In order to examine alterations in the mobilization of EPCs from the bone marrow we measured plasma VEGF.
Main Results
Twenty-three patients with IPF and fifteen healthy subjects were included. The number of early EPCs colonies was markedly reduced in IPF patients vs controls (6.00±6.49 vs 49.68±16.73, respectively, p<0.001). EPCs were further decreased in patients presenting systolic pulmonary arterial pressure (sPAP)≥35 mmHg. The number of colonies per well correlated negatively with P(A-a)O2 (r =  −0.750, p<0.001). Additionally, VEGF mRNA levels were significantly increased in IPF patients. There were no differences observed in VEGF plasma levels in IPF patients when compared to controls.
The current data suggest that inadequate levels of early EPCs may potentially contribute to suppressed repair and recovery of the damaged pulmonary endothelium and thereby may drive the sequence of events in profibrogenic direction. Increased VEGFmRNA levels in the clinical context of IPF may represent a compensatory mechanism to overcome reduced EPCs levels.
PMCID: PMC3544914  PMID: 23341966
5.  Matrix metalloproteinases 2 and 9 increase permeability of sheep pleura in vitro 
BMC Physiology  2012;12:2.
Matrix metalloproteinases (MMPs) 2 and 9 are two gelatinase members which have been found elevated in exudative pleural effusions. In endothelial cells these MMPs increase paracellular permeability via the disruption of tight junction (TJ) proteins occludin and claudin. In the present study it was investigated if MMP2 and MMP9 alter permeability properties of the pleura tissue by degradation of TJ proteins in pleural mesothelium.
In the present study the transmesothelial resistance (RTM) of sheep pleura tissue was recorded in Ussing chambers after the addition of MMP2 or MMP9. Both enzymes reduced RTM of the pleura, implying an increase in pleural permeability. The localization and expression of TJ proteins, occludin and claudin-1, were assessed after incubation with MMPs by indirect immunofluorescence and western blot analysis. Our results revealed that incubation with MMPs did not alter neither proteins localization at cell periphery nor their expression.
MMP2 and MMP9 increase the permeability of sheep pleura and this finding suggests a role for MMPs in pleural fluid formation. Tight junction proteins remain intact after incubation with MMPs, contrary to previous studies which have shown TJ degradation by MMPs. Probably MMP2 and MMP9 augment pleural permeability via other mechanisms.
PMCID: PMC3337816  PMID: 22424238
6.  Pleural Transport Physiology: Insights from Biological Marker Measurements in Transudates 
The aim of this study was to evaluate the physicochemical properties of the pleural mesothelial barrier and of the biological markers that facilitate or eliminate the passage of molecules through the pleura.
Methods and Material:
Pleural fluid samples from sixty-five patients with heart failure were analyzed. The biological markers studied were lactate dehydrogenase (LDH), adenosine deaminase (ADA), interleukin-6 (IL-6), C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), carcinoembryonic antigen (CEA), copper/zinc superoxide dismutase (CuZnSOD), matrix metalloproteinase-2 (MMP-2), -3 (MMP-3), -7(MMP-7), -8 (MMP-8) and -9 (MMP-9). Based on the pleural fluid/serum ratio, these molecules were divided into three groups: a) the LDH-like group with a pleural fluid/serum ratio between 0,4 and 0,8 (LDH, CEA, CuZnSOD, ADA, CRP, MMP-8), b) molecules with a pleural fluid/serum ratio less than 0,4 (MMP-7 and MMP-9) and c) molecules with a pleural fluid/serum ratio equal or above 1 (TNF-α, IL-6, MMP-2 and MMP-3).
No correlation between the molecular radius and the pleural fluid to serum ratio of the above biological markers was found.
The molecular size is not a major determinant for the passage of molecules through the mesothelial barrier. Several other factors may influence the transport of the above molecules to pleural cavity, such as their charge and shape.
PMCID: PMC3204423  PMID: 22114657
Biological markers; mesothelial barrier; pleural fluid/ serum ratio; transudates; lactate dehydrogenase; tumor necrosis factor.
7.  Resting Tension Affects eNOS Activity in a Calcium-Dependent Way in Airways 
Mediators of Inflammation  2007;2007:24174.
The alteration of resting tension (RT) from 0.5 g to 2.5 g increased significantly airway smooth muscle contractions induced by acetylcholine (ACh) in rabbit trachea. The decrease in extracellular calcium concentration [Ca2+]o from 2 mM to 0.2 mM reduced ACh-induced contractions only at 2.5 g RT with no effect at 0.5 g RT. The nonselective inhibitor of nitric oxide synthase (NOS), NG-nitro-L-arginine methyl ester (L-NAME) increased ACh-induced contractions at 2.5 g RT. The inhibitor of inducible NOS, S-methylsothiourea or neuronal NOS, 7-nitroindazole had no effect. At 2.5 g RT, the reduction of [Ca2+]o from 2 mM to 0.2 mM abolished the effect of L-NAME on ACh-induced contractions. The NO precursor L-arginine or the tyrosine kinase inhibitors erbstatin A and genistein had no effect on ACh-induced contractions obtained at 2.5 g RT. Our results suggest that in airways, RT affects ACh-induced contractions by modulating the activity of epithelial NOS in a calcium-dependent, tyrosine-phosphorylation-independent way.
PMCID: PMC1868075  PMID: 17515950
8.  Epithelium-dependent effect of L-glutamate on airways: involvement of prostaglandins. 
Mediators of Inflammation  2002;11(1):33-38.
We investigated the effect of the excitatory amino acid (EAA) receptor agonists L-glutamate, N-methyl-D-aspartate (NMDA), (RS)-a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainic acid on KCl-induced contractions of rabbit tracheal smooth muscle, as well as the role of epithelium and endogenously produced nitric oxide and prostaglandins on these responses. L-Glutamate decreased KCI-induced contractions up to 30%. This effect was attenuated by epithelium removal, tetrodotoxin, methylene blue and indomethacin but not by NG-nitro-L-arginine methyl ester. While NMDA, AMPA and kainic acid had no effect, the combination of NMDA + kainic acid decreased KCI-induced contractions. These results suggest that, in rabbit trachea, L-glutamate has, at least in part, an epithelium-dependent effect mediated via prostaglandin formation and that the EAA receptors involved are non-classical.
PMCID: PMC1781639  PMID: 11926593

Results 1-8 (8)