Atrial natriuretic peptide attenuates flow in an isolated lymph duct preparation

We investigated the hypothesis that atrial natriuretic peptide (ANP) attenuates lymph vessel pumping. In the present experiments, isolated bovine lymphatic vessels were cannulated at each end to create inflow and outflow ports for the administration of Krebs' solution (vehicle) or ANP and for the measurement of fluid pumped by the vessel respectively. Once cannulated, the vessels were placed in a temperature-regulated bath circulated with oxygenated vehicle. Transmural pressure was regulated by the height of a fluid-filled reservoir. Lymph pump activity was assessed by measuring the volume of outflow every ten minutes. ANP was administered at concentrations of 0 (control), 0.1, 1.0, 10 and 100 nM. Data were expressed as a percentage of the value in the control period. When compared with vehicle, ANP produced a significant inhibition of lymph pump activity by 7.7% at 0.1 nM, 24.2% at 10 nM and 38.26% at 100 nM averaged over the hour for which the vessels were exposed to each concentration. Thus ANP inhibits lymph pumping concentration dependently. This may be yet another mechanism by which ANP exerts its haemodynamic effects.