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Functional arrangement of rat diaphragmatic initial lymphatic network

¹Dipartimento di Biologia Strutturale e Funzionale and ²Dipartimento di Scienze Biomediche Sperimentali e Cliniche, Università degli Studi dell'Insubria, Varese, Italy

Submitted 5 December 2005 ; accepted in final form 17 February 2006

Fluid and solute flux between the pleural and peritoneal cavities, although never documented under physiological conditions, might play a relevant role in pathological conditions associated with the development of ascitis and pleural effusion and/or in the processes of tumor dissemination. To verify whether a pleuroperitoneal flux might take place through the diaphragmatic lymphatic network, the transdiaphragmatic pressure gradient (P_TD) was measured in five spontaneously breathing anesthetized rats. P_TD was –1.93 cmH₂O (SD 0.59) and –3.1 cmH₂O (SD 0.82) at end expiration and at end inspiration, respectively, indicating the existence of a pressure gradient directed from the abdominal to the pleural cavity. Morphometrical analysis of the diaphragmatic lymphatic network was performed in the excised diaphragm of three additional rats euthanized with an anesthesia overdose. Optical and electron microscopy revealed that lymphatic submesothelial lacunae and lymphatic capillaries among the skeletal muscles fibers show the ultrastructural features of the so-called initial lymphatic vessels, namely, a discontinuous basal lamina and anchoring filaments linking the outer surface of the endothelial cells to connective tissue or to muscle fibers. Primary unidirectional valves in the wall of the initial lymphatics allow entrance of serosal fluid into the lymphatic network preventing fluid backflow, while unidirectional intraluminar valves in the transverse vessels convey lymph centripetally toward central collecting ducts. The complexity and anatomical arrangement of the two valves system suggests that, despite the existence of a favorable P_TD, in the physiological condition no fluid bulk flow takes place between the pleural and peritoneal cavity through the diaphragmatic lymphatic network.

intraluminar lymphatic pressure; serosal fluid pressure; tissue fluid homeostasis

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				A. Moriondo, F. Bianchin, C. Marcozzi, and D. Negrini Kinetics of fluid flux in the rat diaphragmatic submesothelial lymphatic lacunae Am J Physiol Heart Circ Physiol, September 1, 2008; 295(3): H1182 - H1190. [Abstract] [Full Text] [PDF]

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