Constriction of perfused lymphatics by acetylcholine, bradykinin and histamine

We have previously reported that perfused lymphatic vessels in the canine forelimb constrict in response to increased sympathetic nerve activity or local infusions of endogenous vasoconstrictor substances. In the present study we have assessed the effects of three endogenous vasodilators; acetylcholine, bradykinin and histamine on lymphatic vessel contractility. Each one of these agents, when infused intralymphatically, produced lymphatic constriction as evidenced by significant increases in lymphatic perfusion pressure. The threshold concentrations which produced lymphatic constriction were between 10(-6) and 10(-5) molar for acetylcholine and bradykinin and between 10(-5) and 10(-4) molar for histamine. Surgical exclusion of the lymph nodes and efferent lymph vessels from the perfused tissue did not significantly affect the observed response, indicating that the response occurs predominately in the prenodal segments of the lymphatic system. Infusion of acetylcholine and bradykinin into the arterial supply to the forelimb did not significantly alter lymphatic perfusion pressure, unlike the response seen when catecholamines are infused intra-arterially. Histamine displayed an unusual property in that it constricts lymph vessels upon initial administration but was thereafter completely ineffective. Constriction of lymphatic vessels by substances which are potent vasodilators clearly indicates that significant functional differences exist in endothelial cell/smooth muscle relationships between blood vessels and lymph vessels.