Physiology of human lymphatic contractility: a historical perspective.

The lymphatic system is a transport system that has important roles in fluid/macromolecule homeostasis, lipid absorption, metastasis and immune function. It accomplishes these roles via the generation of a regulated lymph circulation which is dependent upon valves and pumps to overcome the normal fluid pressure gradients. Lymphatic contractility plays crucial roles in the regulation and generation of lymph transport. Whereas our understanding of lymphatic contractility in humans is somewhat limited, a number of studies both in situ and in vitro have provided important insights into the presence and modulation of lymphatic contractility. These studies have clearly demonstrated that lymphatic vessels from a number of different human tissues possess both tonic and phasic changes in contractility. These changes in contractility are presumably involved in the generation and regulation of lymph flow. It has been shown that human lymphatic contractility can be influenced by a number of neural and humoral agents as a means to control lymph transport. However our understanding of the physical and chemical factors which regulate both the spontaneous pumping activity and the vessel tone are more limited. An understanding of thefactors which regulate human lymph transport could provide valuable information on human biology that could be of benefit to the treatment and prevention of diseases.

[Contractions of the lymphangion under low filling conditions and the absence of stretching stimuli. The possibility of the sucking effect]. / Sokrashcheniia limfangionov pri malom napolnenii i pri otsutstvii rastiagivaiushchikh stimulov. Vozmozhnost' prisasyvaiushchego éffekta.

Regulation of the function of the lymphatic pump is tightly connected to the degree of filling of the lymphangion. This mechanism is one of the principle ways that the lymphatics self-regulate lymph transport. But interpretation of the causes and consequences of this regulation is still far from perfect. The issue of whether automatism of electrical activity of the lymphatic smooth muscle cells or the distension of the cell membranes first causes depolarization, is a principal question which needs answering in order to understand the control of lymph transport. In our experiments with perfused isolated bovine mesenteric lymphangions, different values of lymph pressure were simulated. For this purpose, lowfrequency sinusoidal fluctuations of the input pressure were applied to lymphangions under conditions of regulated filling. A poor correlation was seen between lymph pressure fluctuations and lymphangion contractions, as well as between the rate of lymphangion filling and contractions. We observed stable spontaneous contractions of both bovine and rat mesenteric lymphangions at 0 cm of water intralymphatic pressure, and in the absence of distension stimuli (both radial and axial stretch). Under conditions of low filling, contractions of bovine lymphangions produced negative intralymphatic pressure and a suction effect. The automatism is an inherent feature of the lymphatic smooth muscle cells. Distension of the lymphangion modulates the electrical characteristics of the membranes and thus the contractile mechanisms in lymphangions.

[The types of contractions of the lymphangions]. / Tipy sokrashchenii limfangionov.

Four versions of lymphangions contractions were revealed in a single isolated bovine mesentery: longitudinal, total circular, partial circular and uniform. Authentic distinctions in realisation by lymphangions of their pump function depending on a type of the contraction, were absent. The type of contraction seems to be determined by an orientation of the smooth muscle cell bunches in the lymphangion's wall.

[The mechanism of the formation of a reverse fluid filling in the lymphangions]. / Mekhanizm formirovaniia obratnogo zabrosa zhidkosti v limfangionakh.

In the experiments with perfusion of isolated bovine mesenteric lymphangions, values and duration of reversed fluid output were compared with volume and duration of systolic output. The data obtained suggest absence of the isometric contraction phase in bovine mesenteric lymphangion's systole in reversed output.

[The pump function of the lymphangion and the effect on it of different hydrostatic conditions]. / Nasosnaia funktsiia limfangiona i vliianie na nee razlichnykh gidrostaticheskikh uslovii.

In isolated bovine mesenteric lymphangions, the dependence of their productivity on the values of the end-diastolic pressure and the gradients of hydrostatic pressure, was revealed. The maximum of a lymphangion's productivity took place about 10 cm H2O of intravascular pressure. Negative hydrostatic gradient depressed the pump function whereas positive one activated it. Variable hydrodynamic pressure gradients seem to exist in lymphatic vessels.