title: Preferential distribution of leukocytes in rat mesentery microvessel networks.
abstract: Distribution of leukocytes in rat mesenteric microvessel networks was studied using intravital fluorescence video microscopy. A digital image analysis system was used to measure vessel diameters, flow velocities and leukocyte fluxes in 306 capillaries of 8 networks. Capillaries were defined as vessel segments connecting divergent to convergent branch points. Their topological position within the network was quantified by a generation number defined as the number of bifurcations between the capillary and the arteriole feeding the network. Proximal capillaries (generation numbers 4 and 5) were slightly but significantly smaller in diameter (8.9 +/- 0.4 micron, mean +/- SEM) than distal ones (generation numbers 20 and 21, 10.1 +/- 0.4 micron). Average capillary flow velocity decreased markedly from 2.0 +/- 1.0 mm.s-1 in proximal to 0.41 +/- 0.06 mm.s-1 in distal capillaries. Average leukocyte concentration was 3.4 +/- 0.5.10(9) 1(-1) and thus significantly below systemic values (6.0.10(9) 1(-1] in proximal capillaries, and above in distal ones (11.7 +/- 2.6.10(9) 1(-1). The analysis of flow and leukocyte flux partition at 138 bifurcations showed preferential distribution of leukocytes to the daughter capillary with higher flow rate. This suggests a tentative explanation for the observed leukocyte accumulation along the microvascular tree: due to their low fractional flow, proximal capillaries draw relatively leukocyte-poor blood from the arteriole feeding the network; this leads to an increased leukocyte concentration in distal capillaries. As a consequence of the concomitant increase of capillary diameter with increasing generation number, leukocytes are preferentially flowing through larger capillaries and are excluded from small ones.
authors.affiliation: Department of Physiology, Freie Universität Berlin.
authors.forename: K
authors.initials: K
authors.lastname: Ley
authors.forename: A R
authors.initials: AR
authors.lastname: Pries
authors.forename: P
authors.initials: P
authors.lastname: Gaehtgens
mesh_terms: D000818:Animals; D002196:Capillaries / Q000648:ultrastructure; D007962:Leukocytes / Q000648:ultrastructure*; D008297:Male; D008643:Mesentery / Q000098:blood supply*; D008833:Microcirculation; D008856:Microscopy, Fluorescence; D051381:Rats; D011919:Rats, Inbred Strains