Effects of bradykinin on lymphatic pumping in rat mesentery

The effects of bradykinin on lymphatic pump activity of rat mesenteric collecting duct were studied, and the receptor subtype responsible for the bradykinin response was evaluated. Rats were anesthetized with intraperitoneal alpha-chloralose and urethan, and exteriorized mesenteries were studied using intravital microscopic techniques. The diameter of the collecting lymph vessels (approximately 100 microns) was continuously monitored and lymphatic pump parameters (end diastolic diameter, end systolic diameter, stroke volume index, ejection fraction, contraction frequency, and pump flow index) were calculated. Bradykinin (0.1-1.0 nM) did not affect end diastolic diameter, end systolic diameter, stroke volume index, and ejection fraction. Bradykinin increased lymphatic contraction frequency and pump flow index in a dose-dependent manner. Des-Arg9-[Leu8]bradykinin (B1 antagonist, 0.1 microM) had no effect on baseline lymphatic pumping but completely inhibited the bradykinin-induced increase in contraction frequency. N-acetyl-D-Arg-[Hyp3,Thi5,8,D-Phe7] bradykinin (B2 antagonist, 0.1 microM) significantly depressed lymphatic contraction frequency in baseline conditions but had no effect on bradykinin-induced increases in contraction frequency. These results indicate that bradykinin induces positive chronotropic but not inotropic effects on lymphatic pump activity through the stimulation of B1 receptors.