Intrinsic pumping of mesenteric lymphatics is increased after hemorrhage in awake sheep

Lymphatic vessels have the ability to contract and transport liquid and protein from tissue spaces to the intravascular space. The purpose of this investigation was to test whether this lymph pump is stimulated following a fixed volume hemorrhage in awake sheep. To quantitate lymphatic pumping in vivo, a mesenteric lymphatic was isolated from all lymph input and provided with Krebs solution at a fixed transmural pressure. A branch of the mesenteric duct was cannulated to provide a measure of lymph flow rate. Each animal was either bled 25% of blood volume over 5 min or was observed. Systemic arterial blood pressure declined in all bled sheep (P < 0.05). Hemorrhage had no effect on lymph flow from mesenteric ducts. However, hemorrhage significantly enhanced lymphatic pumping, approximately 200% of control values 3 hr after hemorrhage (P < 0.01). Increased lymphatic pumping after hemorrhage may play an important role in blood volume and protein restitution.