Evidence That the L-Arginine Pathway Plays a Role in the Regulation of Pumping Activity in Bovine Mesenteric Lymphatic Vessels

Abstract

The objective of this study was to investigate the role of the L-arginine pathway in the regulation of lymphatic pumping. Bovine mesenteric lymphatic vessels (8 to 12 cm in length containing four to six lymphangions) were immersed in an organ bath with input provided by a reservoir filled with Krebs solution. The vessels were stimulated to pump by applying a 6 cm H 2O transmural pressure. The addition of 10 -7-10 -4 M oxyhemoglobin, N G-monomethyl-L-arginine (L-NMMA), or methylene blue to the reservoir resulted in a reduction in lymphatic pumping. L-Arginine (10 -7-10 -4 M) had no effect on spontaneous pumping activity. However, L-arginine reversed the inhibition caused by oxyhemoglobin and L-NMMA. When tested between 10 -7 and 10 -6 M, sodium nitroprusside (sNP) had variable effects on lymphatics. sNP depressed pumping in approximately 2 3 of the vessels and increased pumping in the remaining 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-NMMA, and methylene blue whereas the higher concentration (10 -6 M) caused further reductions in pumping activity. These results suggest that bovine lymphatic vessels produce nitric oxide or a related compound. L-Arginine metabolites appear to facilitate the pumping response by an as yet undefined mechanism.