Open interfaces in initial lymphatics: a methodological artifact?

Castenholz, Hauck, and other authors--including myself--have previously described initial lymphatics and the existence of open interfaces in tongue, mesentery as well as in uterus. These structures were supposed to represent an additional entrance into the initial lymphatic pathway and the open interfaces were proposed to act as pressure relief valves in some organs in case of increased volumes of tissue fluid. The methodological approaches used by these authors were interstitial and retrograde fillings of the lymphatic system, and often an endothelium-lined structure was seen connecting initial lymphatics with the interstitial space and ending free in connective tissue. Further research of my group in basic lymphology has led to new and surprising insights, and we now demonstrate that most of these so called "open-interfaces" are methodological artifacts.

Initial lymphatics--morphology and function of the endothelial cells.

In considering lymph formation, the function of the initial lymph sinus is usually considered a passive process. The cells, however, of the initial lymphatics hold a key position in absorbing fluid from the interstitial space. The present study using rats and guinea pigs in different days of the estrus cycle or pregnancy examined by light, scanning electron, and transmission electron microscopy suggests that the forming and closing of the open-junction formations is an active component of the lymphatic endothelium. Open-interface structures represent a further entry into initial lymphatic pathways. The existence of "endothelial cellular buds" probably act structurally to build elements of the initial lymph sinus. In short, the endothelium of the initial lymphatic sinus appears to be a structure of utmost flexibility able to respond promptly to increased amounts of lymph fluid transported from the interstitial space.

[Development of the lymphatic system in the animal kingdom]. / Der Aufbau des Lymphgefässsystems im Tierreich.

This article gives a compact and simplified survey of the organization of the lymphatic vascular system or equivalent structures in animals resulting in the question how the phylogenetic evolution could have been.

Formation and morphology of Reissner's fibre in primates. A scanning electron microscopic study.

The subcommissural ependyma of the third ventricle, the rhomboid fossa, and the central canal of the spinal cord were examined in Tupaia, Saimiri, and Cebus by scanning electron microscopy. In all three species studied, fine filaments, granules, and amorphous masses were found at the surface of the subcommissural ependyma representing the original structures of the Reissner's fibre (RF). Bundles of filaments or net-like structures ultimately forming a compact secretory plate develop in the caudal part of the secretory zone. In Tupaia and Saimiri, the secretion collects in a groove-like depression in the centre of the dorsal ventricular wall. In Cebus two secretory pathways occur in the lateral sulci, which eventually merge together in the aqueduct. In the rhomboid fossa and the spinal cord, the RF is in close contact with the ependyma, and its surface is longitudinally grooved and covered with granular material and cells. The present scanning electron microscopic findings speak in favour of a merocrine type of secretion in the apical region of the ependymal cells. Ciliary movement and flow of cerebrospinal fluid are assumed to be the most important factors regulating the formation of the RF.

[Functional morphologic mechanisms of lymph transport]. / Funktionsmorphologische Mechanismen des Lymphtransportes.

The phenomenon of the lymph flow in the initial lymphatics and lymphangions of collecting vessels has been studied. Special attention was paid to the structural features and functional mechanisms of the lymphatic vascular system as well as the influence of extravascular factors on the lymphatic flow. In this context, a survey of the current knowledge of functional-morphological research in lymphology is given which may lead to a better understanding of a disturbed lymph flow under pathophysiological conditions.

[New knowledge of the structural principle of lymph formation]. / Neue Erkenntnisse zur strukturellen Grundlage der Lymphbildung.

The structural conditions in the zone of transition from the tissue to the lymphatics are described on the basis of electron microscopic (especially scanning electron microscopic) and light microscopic results. Here, the interstitium with its fiber organization and the system of prelymphatic channels as well as the wall characteristics of the initial lymphatics and precollectors are given particular consideration. The flow conditions, the stretching ability and the permeability of the very fine lymphatics are investigated in the model of the rat tongue by means of a special vital microscopic technique using various labelling substances. Against the background of the morphological and rheological findings, the question of lymph formation is analysed on the basis of new hypothetical criteria for the mechanisms involved.

The sublingua and tongue of Tupaia (Scandentia, Mammalia): a scanning electron microscope study.

The surface morphology of the tongue and the sublingua in Tupaia belangeri was examined both under the dissection microscope and with the scanning electron microscope. Shape and structural differentiation of the sublingua and the anterior ventral part of the tongue are described. Special types of papillae were found on the lingual segment of the keel, along the serrated edges of the sublingua, and at the apex linguae. The findings are discussed with respect to the special conformation of the oral cavity of Tupaia and in relation to the evolutionary and functional significance of the tongue and the sublingua in this species.

The stimulation of arachidonic acid metabolism by organic lead and tin compounds in human HL-60 leukemia cells.

The liberation of fatty acids, above all arachidonic acid, in human blood cells is involved in numerous health problems or physiological mechanisms. The activity of cellular phospholipases leads to lipid metabolites such as eicosanoids, platelet activating factor, diacylglycerol, and inositolphosphates that are capable of mediating such pathological symptoms. The results presented here demonstrate that organic heavy metal compounds induce arachidonic acid liberation or its rearrangement within the lipid classes of HL-60 cells before a loss in viability can be detected. Four of the compounds tested, triethyllead (Et3Pb+), diethyllead (Et2Pb2+), trimethyllead (Me3Pb+), and trimethyltin (Me3Sn+), show a threshold concentration at which the viability of the cells is drastically decreased after 60 to 180 min incubation, whereas dibutyltin (But2Sn2+) induces a constant increase of cell death during the whole incubation time. In the case of threshold concentrations, the compounds stimulate a loss of arachidonic acid within the phospholipids and an increase of free fatty acid and eicosanoids before cell death could be detected. An important fact is the rearrangement of arachidonic acid within the lipid classes of these cells induced by metal concentrations that were not able to kill the cells within the given time. Primarily affected is phosphatidylethanolamine which loses arachidonic acid and, to a minor extent, phosphatidylcholine. Portions of the liberated fatty acid were then metabolized and/or shifted into neutral lipids and other phospholipids. All compounds tested show comparable effects, although at different concentrations. The toxicities of the compounds can be ordered as follows: Et3Pb+ greater than or equal to Et2Pb2+ greater than But2Sn2+ greater than or equal to Me3Pb+ much greater than Me3Sn+ greater than or equal to Pb2+. The cellular shape change following incubation with metal compounds is a further strong indication of a change in the membrane lipids. The cells lose their characteristic microvilli and/or blebs and become round without a loss in viability.