EVIDENCE THAT THE L-ARGININE PATHWAY PLAYS A ROLE IN THE REGULATION OF PUMPING ACTIVITY IN BOVINE MESENTERIC LYMPHATIC VESSELS

The objective of this study was to investigate the role of the L-argin ine pathway in the regulation of lymphatic pumping. Bovine mesenteric lymphatic vessels (8 to 12 cm in length containing four to six lymphan gions) were immersed in an organ bath with input provided by a reservo ir filled with Krebs solution. The vessels were stimulated to pump by applying a 6 cm H2O transmural pressure. The addition of 10(-7)-10(-4) M oxyhemoglobin, N-G-monomethyl-L-arginine (L-NMMA), or methylene blu e to the reservoir resulted in a reduction in lymphatic pumping. L-Arg inine (10(-7)-10(-4) M) had no effect on spontaneous pumping activity. However, L-arginine reversed the inhibition caused by oxyhemoglobin a nd L-NMMA. When tested between 10(-7) and 10(-6) M, sodium nitroprussi de (sNP) had variable effects on lymphatics. sNP depressed pumping in approximately 2/3 of the vessels and increased pumping in the remainin g 1/3 of ducts. When the results were meaned, sNP caused a significant depression in activity. However, the lower concentration of sNP (10(- 7) M) was able to reverse the inhibitory effects of oxyhemoglobin, L-N MMA, and methylene blue whereas the higher concentration (10(-6) M) ca used further reductions in pumping activity. These results suggest tha t bovine lymphatic vessels produce nitric oxide or a related compound. L-Arginine metabolites appear to facilitate the pumping response by a n as yet undefined mechanism. (C) 1995 Academic Press, Inc.