ENDOTHELIN AND NITRIC-OXIDE SYNTHASE IN LYMPHATIC ENDOTHELIAL-CELLS -IMMUNOLOCALIZATION IN-VIVO AND IN-VITRO

Background: Endothelin (ET) is an endothelium-derived multifunctional peptide that produces a potent, long-lasting vasoconstriction, Nitric oxide (NO), besides being the most important endothelium-derived relax ant factor in blood vessels, is supposed to be involved in regulating the interactions among endothelium, adhesive molecules, and leukocytes . Methods: We investigated the possible occurrence and distribution of ET and constitutive nitric oxide synthase (NOs), the enzyme that gene rates NO from L-arginine, in bovine lymphatic vessels and primary cult ure of lymphatic endothelium by using immunocytochemistry. Results: Sp ecific immunostaining with both ET and endothelial constitutive NOs an tisera was detectable at light and electron microscopic levels in the endothelial cell layer of lymphatic vessels, whereas no immunostaining could be observed in the muscular and adventitial layers, The immunor eaction showed a diffuse pattern throughout the cytoplasm of endotheli al cells, Primary cultures of endothelial cells isolated from lymphati c vessels also displayed cytoplasmic ET- and NOs-like immunoreactiviti es, The endothelial nature of cell monolayers was confirmed by the pos itive reaction to the von Willebrand factor, a reliable marker of endo thelial cells, and by ultrastructural features of cultured cells. Conc lusions: These findings suggest that the endothelium is a major source of ET and NO in lymphatic vessels, Interestingly, the lymphatic endot helium maintains the capability of producing such vasoactive sustances also in vitro, thus suggesting that lymphatic endothelial cells in cu lture may be used in studies concerning the role of the endothelium in the generation of vasoactive molecules, According to previous functio nal studies, the occurrence of ET and NOs immunoreactivities in lympha tic vessel endothelium supports the view that lymphatic endothelium ma y play an important role in the regulation of lymphatic vascular tone and in the production of vascular contractile activity promoting lymph flow.