Serotonin-induced visualization of the popliteal lymph node by angiography. A unique microvascular response to...

Regulation of the blood supply to lymph nodes is an important determinant of lymphocyte traffic but remains poorly understood. Infusion into the femoral artery of serotonin (5 HT), an agent that may produce either vasoconstriction or vasodilatation, induced striking arteriographic visualization of the popliteal lymph node in 19 of 20 dogs. Neither other vasodilator agents (acetylcholine, tolazoline, histamine, isoproterenol, sodium arachidonate, the prostaglandin analog CL115, 347) nor vasoconstrictor substances (norepinephrine, epinephrine, phenylephrine, and ergonovine maleate) produced the same effect. The timing of appearance and disappearance of the contrast medium during 5HT infusion suggests that an increase in capillary blood flow secondary to arteriolar dilatation in the lymph node is responsible for the augmented visualization. 5HT-induced visualization of the popliteal lymph node was not modified by pretreatment with either the specific 5HT-2 antagonist ketanserin or the nonspecific antagonist methysergide. The specificity of action of 5HT and its availability for release from circulating and noncirculating cellular elements suggest that it may be important in the regulation of lymph node circulation, and thereby, lymphocyte traffic. This approach may provide another means to enhance the visualization of lymph nodes.