Physiological roles of endogenous nitric oxide in lymphatic pump activity of rat mesentery in vivo

Physiological roles of endogenous nitric oxide (NC) in the lymphatic pump a ctivity of rat mesenteries in vivo were evaluated using an intravital video microscope system. Changes in the pumping frequency (F), the end diastolic diameter (EDD), and the end systolic diameter (ESD) of the mesenteric lymp h microvessels were measured with the microscope system and then the pump f low index (PFI) was calculated. A 15-min superfusion of 30 mu M N-omega-nit ro-L-arginine methyl ester (L-NAME) in the mesenteries caused significant i ncreases off and PFI and a significant decrease of the EDD and ESD, Simulta neous superfusion of 1 mM L-arginine with 30 mu M L-NAME produced a signifi cant reversal of the L-NAME-mediated increase of F and decrease of ESD. A 1 5-min superfusion of 100 mu M aminoguanidine caused no significant effects on F, EDD, and ESD of the mesenteric lymph vessels in vivo. These findings suggest that endogenous NO has physiologically modulated the lymphatic pump activity in rat mesentery in vivo and that the production and release of N O may be mediated by constitutive NO synthase but not by inducible NO synth ase.