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 fo r the bradykinin response was evaluated. Rats were anesthetized with i ntraperitoneal alpha-chloralose and urethan, and exteriorized mesenter ies were studied using intravital microscopic techniques. The diameter of the collecting lymph vessels (similar to 100 mu m) was continuousl y monitored and lymphatic pump parameters (end diastolic diameter, end systolic diameter, stroke volume index, ejection fraction, contractio n frequency, and pump flow index) were calculated. Bradykinin (0.1-1.0 nM) did not affect end diastolic diameter end systolic diameter, stro ke volume index, and ejection fraction. Bradykinin increased lymphatic contraction frequency and pump flow index in a dose-dependent manner. Des-Arg(9)-[Leu(8)]bradykinin (B-1 antagonist, 0.1 mu M) had no effec t on baseline lymphatic pumping but completely inhibited the bradykini n-induced increase in contraction frequency. -acetyl-D-Arg-[Hyp(3),Thi (5,8),D-phe(7)]bradykinin (B-2 antagonist, 0.1 mu M) significantly dep ressed lymphatic contraction frequency in baseline conditions but had no effect on bradykinin-induced increases in contraction frequency. Th ese results indicate that bradykinin induces positive chronotropic but not inotropic effects on lymphatic pump activity through the stimulat ion of B-1 receptors.