Bradykinin, a vasodilator, increases permeability to macromolecules in postcapillary venules. Recent studies indicate that vasodilators elevate water flux from frog mesenteric capillaries. Thus we hypothesized that bradykinin would also increase transcapillary water flux. Arteriolar (ac), true (tc), and venular (vc) capillaries were identified within the microvascular network of frog mesentery. Each capillary was cannulated in situ and perfused with control (frog Ringer and 10 mg/ml bovine serum albumin) and then bradykinin test (10(-7) M) solutions. Hydraulic conductivity (Lp) increased across the network (1.8, 5.3, and 11.0 x 10(-7) cm.s-1.cmH2O-1 for ac, tc, and vc, respectively). Bradykinin test Lp normalized to control (LpBKN/LPC) was elevated threefold (n = 37). Lp for ac (n = 12) was elevated 3.5-fold and oscillated with time. Lp for tc (n = 13) increased fivefold within the first 5 min of exposure and then dropped. Lp for vc (n = 12) was not different from control. Location- and time-dependent responses of Lp indicate that capillaries forming microvascular networks have individual responses to bradykinin.