Characteristics of the active lymph pump in bovine prenodal mesenteric lymphatics.
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BACKGROUND: The functional characteristics of the bovine mesenteric postnodal lymphatics are well-described. However there are no reports of pumping characteristics of the bovine mesenteric prenodal lymphatics. We propose that the prenodal lymphatics have adapted to the local conditions of lymph flow and are functioning differently than the postnodal vessels. METHODS AND RESULTS: To evaluate pumping in bovine prenodal mesenteric lymphatics, we observed their contractility in response to the changes in transmural pressure and imposed flow. Lymphatics (diameter approximately 460 microm) were isolated, cannulated, and pressurized. Lymphatic diameters were traced from video records; the lymphatic tone index, contraction amplitude and frequency, lymphatic pump indices were calculated. Increasing transmural pressure from 3 to 6 cm H2O produced a strong inotropic response, but did not induce a significant chronotropic response. Pumping reached its maximum at transmural pressures 6-9 cm H2O and was not significantly depressed up to 15 cm H2O, whereas pumping in postnodal lymphatics is typically depressed at transmural pressures higher than 10 cm H2O. Bovine prenodal mesenteric lymphatics also demonstrated very low sensitivity to the increases in imposed flow. CONCLUSIONS: We concluded that the functional heterogeneity exists on the intraregional levels in lymphatic nets.
