Leukocyte flow dynamics in the rat liver microcirculation

The flow dynamics of leukocytes in the rat liver microcirculation was studied in the sinusoids in the three zones of the liver acinus (zone 1, periportal; zone 2, mid; and zone 3, pericentral) by means of in vivo fluorescence microscopy. Leukocytes were labeled in vivo with acridine orange. The microscopic image was videotaped and on playback of the videotapes, leukocyte velocity, leukocyte flux, erythrocyte velocity, sinusoid diameter, and sinusoid tortuosity were measured. Blood flow and flow resistance were calculated from these data. The leukocyte velocity, erythrocyte velocity, sinusoid diameter, and blood flow in the liver sinusoids in zone 3 were significantly greater than those in zone 2, which in turn were also significantly greater than those in zone 1. There were significant positive correlations between leukocyte and erythrocyte velocity, between leukocyte velocity and sinusoid diameter, and between leukocyte velocity and blood flow. Sinusoid tortuosity in zone 1 was significantly larger than that in zone 2 and zone 3. Flow resistance in zone 1 was significantly greater than that in zone 2, which was also significantly greater than that in zone 3. These results provide evidence for a "zonal gradient" of leukocyte velocity in the liver sinusoids, with increasing velocity from zone 1 to zone 3. The morphological (narrow diameter and tortuous path) and resistance factors appear to contribute to the slow velocity in zone 1.