Pericardium of the frog, Rana esculenta, is morphologically designed as a lymphatic space

Abstract

The importance of the pericardium and the pericardial fluid (PF) in the control of cardiac function has emerged over the past few years. Despite the acknowledgment that amphibians are exposed to both dehydration and excessive water accumulation, nothing is known about their pericardial structure and the morphological basis of the PF formation. We have studied the parietal pericardium (PP) morphology in Rana esculenta by electron microscopy. SEM images of the inner surface, which lines the pericardial cavity, revealed the presence of large vesicles and many small circular openings. TEM observations showed that the PP is made up of an inner mesothelial lining, often constituted by two layers of very flat cells lying on a basal membrane and of regularly oriented collagen bundles. The PP outer surface is lined by a layer of flat cells, without a basal membrane. The mesothelial cells had overlapping boundaries with complex intercellular connections and a rich pool of caveolae opened in the direction of both the pericardial cavity and intercellular spaces. These cells indicate an intense intracellular and/or intercellular transfer of fluids and substances. The intraperitoneal injection of the idromineral hormone, Val 5 -ANG II, induced PP modifications, particularly evident at the level of the structures involved in the transmesothelial traffic. These lymphatic-like traits suggest that the frog PP represents a large lymphatic sac, subject to paracrineendocrine remodeling, which can actively adjust the PF, influencing the composition and volume of the myocardial interstitial fluid.

Increased Level of Pericardial Insulin-Like Growth Factor-1 in Patients With Left Ventricular Dysfunction and Advanced Heart Failure

“…The pericardial space is a large lymphatic sac, and the composition of the pericardial fluid is influenced by the myocardial interstitial fluid (16). Laham et al (17) reported that intrapericardial delivery provides markedly higher myocardial deposition and retention than intracoronary or intravenous delivery.…”

Development of the lymphatic vascular system: A mystery unravels

“…In birds and, more prominently, in mammals, lymph nodes were added for important functions in acquired immunity. Although the zebrafish model provides an extremely valuable experimental tool for research into the development of the blood vascular system, there is no well-defined lymphatic system in zebrafish, and Xenopus (frogs) have long served as an excellent experimental model for studies of the development and function of the lymphatic vascular system (Day et al, 1963;Koyama and Horimoto, 1988;Greber and Schipp, 1990;Baldwin et al, 1993;Ohtani et al, 2001;Cerra et al, 2003). In this review, we will discuss several genes that recently have been found to play essential roles in early mammalian lymphatic development and in lymphatic function, with particular attention to mutant phenotypes in mice and humans.…”