Reflex modulation of lymphatic pumping in sheep.

Lymphatic pumping activity was examined in halothane-anesthetized sheep. A doubly cannulated preparation of the mesenteric lymph duct was "isolated" from lymph input, other than that from a constant pressure reservoir of artificial lymph attached to its inflow cannula, but had its blood supply and innervation intact. A cerebral ischemic response, evoked by injection of 2 ml air into the common carotid artery, increased both mean arterial pressure and fluid propulsion by the lymphatic. The latter rose from a control value of 45 microliters/min to a peak of 74 microliters/min. When 10(-4) M phentolamine was introduced into the lymphatic lumen, there was a transient increase followed by a sustained fall in lymph pumping. Repetition of the air injection while phentolamine was present in the duct lumen produced no increase in lymph pumping. In adrenalectomized animals, resting lymph propulsion by the mesenteric duct was depressed, and the response to air injection was attenuated but remained significantly greater than control. These results suggest that reflex activation of the sympathetic nervous system can increase lymph propulsion and that this may be augmented by the release of circulating catecholamines.