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Department of Biophysics, University of Rochester, Rochester, New York 14642
Received 19 June 1996; accepted in final form 20 June 1996.
Frame, Mary D. S., and Ingrid H. Sarelius. Endothelial
cell dilatory pathways link flow and wall shear stress in an intact
arteriolar network. J. Appl. Physiol.
81(5): 2105-2114, 1996.
Our purpose was to determine whether the
endothelial cell-dependent dilatory pathways contribute to the
regulation of flow distribution in an intact arteriolar network. Cell
flow, wall shear stress (T
),
diameter, and bifurcation angle were determined for four sequential
branches of a transverse arteriole in the superfused cremaster muscle
of pentobaribtal sodium (Nembutal, 70 mg/kg)-anesthetized hamsters
(n = 51). Control cell flow was
significantly greater into upstream than into downstream branches
[1,561 ± 315 vs. 971 ± 200 (SE) cells/s,
n = 12]. Tissue exposure to 50 µM
N-nitro-L-arginine + 50 µM indomethacin (L-NNA + Indo) produced arteriolar constriction of 14 ± 4% and decreased
flow into the transverse arteriole. More of the available cell flow was
diverted to downstream branches, yet flow distribution remained
unequal. Control T was higher
upstream than downstream (31.3 ± 6.8 vs. 9.8 ± 1.5 dyn/cm2).
L-NNA + Indo decreased
T upstream and increased
T downstream to become equal in
all branches, in contrast to flow. To determine whether constriction in
general induced the same changes, 5%
O2 (8 ± 4% constriction) or
10
9 M norepinephrine (NE;
4 ± 3% constriction) was added to the tissue (n = 7). With
O2, flow was redistributed to
become equal into each branch. With NE, flow decreased progressively
more into the first three branches. The changes in flow distribution
were thus predictable and dependent on the agonist. With
O2 or NE, the spatial changes in
flow were mirrored by spatial changes in
T. Changes in diameter and in
cell flux were not related for
L-NNA + Indo (r = 0.45),
O2
(r = 0.07), or NE
(r = 0.36). For all agonists, when the
bifurcation angle increased, cell flow to the branch decreased
significantly, whereas if the angle decreased, flow was relatively
preserved; thus active changes in bifurcation angle may influence red
cell distribution at arteriolar bifurcations. Thus, when the
endothelial cell dilatory pathways were blocked, the changes in flow
and in T were uncoupled; yet when they were intact, flow
and T changed together.
flow-dependent responses; capillary recruitment; bifurcation angle; nitric oxide
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