Regional variations of contractile activity in isolated rat lymphatics

To evaluate lymphatic contractile activity in different regions of the lymphatic system in a single animal model (the rat thoracic duct, mesenteric, cervical, and femoral lymphatics) in response to changes in lymph pressure and flow.

The systolic and diastolic diameters of isolated, cannulated, and pressurized lymphatic vessels were measured. Contraction frequency, ejection fraction, and fractional pump flow were determined. The influences of incrementally increased transmural pressure (from 1 to 9 cm H2O) and imposed flow (from 1 to 5 cm H2O transaxial pressure gradient) were investigated.

The authors determined regional differences in lymphatic contractility in response to pressure and imposed flow. They found the highest pumping (at the optimal pressure levels) in mesenteric lymphatics and lowest pumping in thoracic duct. All lymphatics had their optimal pumping conditions at low levels of transmural pressure. Different degrees of the flow-induced inhibition of the pump were observed in the different types of lymphatics. During high flow, the active lymph pumps in thoracic duct and cervical lymphatics were almost completely abolished, whereas mesenteric and femoral lymphatics still exhibited significant active pumping.

The active lymph pumps in different regions of the rat body express variable relative strengths and sensitivities that are predetermined by different hydrodynamic factors and regional outflow resistances in their respective locations.