Intrinsic propulsive activity of thoracic duct perfused in anesthetized dogs.

Abstract We have investigated the regulation of the intrinsic smooth muscle propulsive activity of the thoracic duct in the anesthetized, ventilated dog. We cannulated both ends of the duct and, with the chest open and ventilation constant, perfused it with Krebs-Henselite buffer at constant inflow and outflow pressures. With inflow and outflow pressures equal (no net driving pressure) flow through the duct must be due to intrinsic smooth muscle contractions. When we increased transmural distending pressure of the thoracic duct, flow increased as distending pressure increased to 5 cm H 2 O, then declined. Although there was no evidence of any basal neural stimulation of the duct, intravenous infusion of catecholamines increased flow. Their effects were blocked by phentolamine (α-blocker). 5-Hydroxytryptamine caused flow to increase, then decrease. The decrease appeared to be due to duct spasm, not inhibition. Constant intravenous infusions of histamine, prostaglandin E 1 , and bradykinin either had no effect or inhibited flow. Intrinsic myogenic activity of the thoracic duct in the living animal may be a significant factor in lymph propulsion.