Pressure fluctuations and lymph flow were measured in cannulated popliteal efferent and metatarsal afferent lymphatics in anaesthetized sheep. 2. Stimulation of the lumbar sympathetic chain at 1.4 and 10 Hz increased lymph flow and lymphatic contraction frequency. These effects were most marked during 10 Hz stimulation where, in some efferent preparations, greater than 5-fold increases in lymph flow and contraction frequency were observed. 3. Strain-gauge plethysmograph recordings in the lymphatic's drainage area indicated that during stimulation blood flow was reduced. There was also a slow continuous fall in tissue volume throughout the periods of stimulation, presumably due to a net uptake of fluid by the blood vessels. 4. Intra-arterial infusion of phentolamine at a rate of 10 micrograms kg-1 min-1 blocked the increases in lymph flow and contraction frequency. 5. These results suggest that the observed increases in lymph flow were due to direct neurogenic stimulation of lymphatic pumping.
