Mesenteric lymph flow responses to splanchnic nerve stimulation in sheep

The main mesenteric lymph duct was cannulated in halothane-anesthetized sheep, and continuous recordings were made of lymph flow, lymphatic pressure fluctuations, and arterial pressure. Stimulation of the left greater splanchnic nerve at frequencies of 1, 4, and 10 Hz caused lymph flow to increase by 30 +/- 9, 74 +/- 19, and 80 +/- 21%, respectively. Lymphatic contraction frequency and mean arterial pressure showed graded increases in response to increasing stimulus frequencies. These responses were reduced after intravenous infusion of phentolamine, suggesting that they were mediated by alpha-adrenoceptors. Lymph protein concentration remained unchanged during stimulation, suggesting that lymph formation in the nodes was not responsible for the increased lymph flow. The lymph flow response during 20 min of stimulation was biphasic, showing an initial transient increase followed by a depression to 45% of control. It is concluded that the initial increase in flow may be explained by stimulation of the lymphatic pump by nerves and/or circulating catecholamines, while the subsequent decrease reflected a reduction in lymph formation.