SUMMARY1. Isolated preparations of bovine mesenteric lymphatics containing about seven valved segments were cannulated and set up in a perfusion system so that, when the preparation was not contracting, the inflow and outflow pressures were exactly equal and there was no flow through the preparation.2. Transmural pressure was varied by raising or lowering the inflow and outflow pressures simultaneously by the same amount.3. The isolated vessels showed rhythmic spontaneous activity; it consisted of quick contractions which spread rapidly over the entire preparation, each followed by a rapid relaxation and a diastolic pause.4. With each contraction, the preparation decreased in both length and diameter and generated an outflow pressure which pumped fluid in the direction determined by the orientation of the values.5. Raising the transmural pressure in the preparation increased the output of the preparation; this was achieved by an increase in both the frequency and force of the individual contractions.6. It was concluded that bovine lymphatics could propel fluid by their intrinsic activity at a rate which was related to the degree of distension of their walls.
Norepinephrine increases the spontaneous contraction frequency of isolated bovine lymphatic vessels but, paradoxically, reduces contraction force. In this investigation contractions were elicited by electrical stimulation, applied as field stimulation or across a sucrose gap. Evoked contractions were not reduced in force by concentrations of norepinephrine that have previously been shown to dramatically reduce contractility in spontaneously active vessels. However, at higher concentrations a beta-inhibitory component of the norepinephrine effect was often observed. Simultaneous recordings of electrical and mechanical activity from spontaneously active vessels showed that each spontaneous contraction was initiated by a single action potential. Norepinephrine significantly disrupted electrical activity causing increased action potential frequency, reduction in action potential amplitude, and frequent failure of full action potential development. We conclude that norepinephrine depresses the force of spontaneous contractions by disruption of spontaneous pacemaking rather than by any direct effect on vessel contractility.
SUMMARY1. Pressure fluctuations and lymph flow were measured in popliteal, prefemoral and mesenteric efferent lymphatic vessels in conscious sheep.2. Intravenous adrenaline infusion increased frequency of lymphatic contraction and lymph flow in all three vessels. In the case of the prefemoral vessels flow remained high after the infusion had stopped.3. Intravenous noradrenaline infusion also increased frequency of contraction and lymph flow in all three vessels but prefemoral flow was depressed after the infusion had stopped.4. Lymphatic frequency of contraction and lymph flow increased when the animals were startled.5. Anaesthetizing the animals with pentobarbitone did not abolish lymphatic contractions, nor did it prevent the response to adrenaline and noradrenaline infusions.6. The most obvious interpretation of these results is that adrenaline and noradrenaline act by increasing frequency and force of pumping of lymphatic vessels.
SUMMARY1. A 20 cm length of the main mesenteric lymph duct in the sheep was cannulated at both ends and measurements were made in both conscious and anaesthetized animals of the ability ofthe duct to pump saline from an inflow reservoir to an outflow at the same height.2. Fluid was propelled only when the lymphatic contracted and this was unaffected by movements of the animal round the cage or by fluctuations in abdominal pressure or by respiratory movements.3. It was confirmed that the mesenteric duct was 'isolated' from the rest of the lymphatic system by closing the inflow tap whereupon fluid propulsion ceased.4. Raising transmural pressure by varying inflow and outflow by the same amount had the effect of increasing fluid output; this was achieved by an increase in both the frequency and force of lymphatic contractions.5. Lymphatic frequency of contraction and fluid output increased when the animals were frightened.6. Intravenous infusions of noradrenaline increased the frequency of lymphatic contraction and increased fluid propulsion, while isoprenaline infusions depressed flow.7. This preparation demonstrates that it is possible to study the control of lymphatic pumping in conscious sheep without the complication of changing rates of lymph formation.
1. Lymph flow and pressure fluctuations were measured by cannulating popliteal efferent and distal hind-limb afferent lymphatic vessels in anaesthetized sheep. The cannula outflow height was raised above the vessels to increase lymphatic outflow pressure. 2. Lymph flow decreased non-linearly as the outflow was raised. The rate of decrease increased with increasing outflow height. 3. Lymphatic contraction frequency rose and stroke volume fell with increasing outflow height. 4. The calculated power necessary to move lymph along the cannula initially increased with outflow height but it reached a peak and was reduced again by raising the outflow further. Calculated lymphatic stroke work followed a very similar pattern. 5. Lymph flow was maintained up to a greater outflow height in afferent than in efferent vessels. Curves relating frequency, power and stroke work to outflow height were shifted to the right in the afferent lymphatics. 6. These results are consistent with an intrinsic lymphatic pump which can be stimulated by increasing pressure. At high pressures, however, the pump fails.
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