Effects of endotoxin on microvascular flow velocity and indicator dispersion

The effects of endotoxin (3mg/kgLD100) on the microcirculation of exposed mesentery were studied in anesthetized cats (0.7 kg). A femoral artery and vein were cannulated for arterial pressure determination and injections. Successive bolus injections (0.05 ml) of blood containing sulphhemoglobin red blood cells (SH-RBC) and fluorescein isothiocyanate-labeled dextran (FITC-Dextran) were made into a mesenteric artery branch. The indicator passage through the microvessels was recorded on videotape. Upon replay, the outputs of an injection signal and two video sampler (VS) intensity-sensitive windows (placed at each end of the vessel) were monitored for obtaining indicator time-concentration curves. The arteriolar flow velocity was calculated as the distance between windows (millimeters) divided by the difference in mean transit time (t) of the two curves. Vessel dimensions were determined as the calibrated distance between the windows. During the first hour postendotoxin, the arterial pressure decreased while arterioles (35 micrometer and larger) and venular diameters increased. Terminal arteriole (20-micrometer)diameters decreased. SH-RBC and FITC-Dextran velocities decreased 50%, t increased, and indicator dispersion increased. Arterial pressure increased to above control levels during the next two hours and 55-micrometers and 35-micrometers arteriolar and venular diameters decreased, and 20 micrometers arterioles increased; SH-RBC and FITC-Dextran flow velocities gradually decreased; arteriolar t increased markedly; and indicator dispersion increased. During the terminal phase, arterial pressure decreased rapidly, all vessel diameters increased, velocities decreased, t markedly increased, and indicator dispersion increased. Control SH-RBC velocities were greater and t were less than for FITC-Dextran.