Mds. Frame et Ih. Sarelius, REGULATION OF CAPILLARY PERFUSION BY SMALL ARTERIOLES IS SPATIALLY ORGANIZED, Circulation research, 73(1), 1993, pp. 155-163
To explore a mechanism for spatial recruitment of capillaries, this st
udy determined whether the arterioles controlling capillary perfusion,
which typically arise as sequential branches along a transverse arter
iole, could respond differently from each other in situ in a spatially
ordered way. Diameter changes were measured for these arterioles at a
known location in the intact microvasculature in the cremaster muscle
of anesthetized Golden hamsters (N=67); each arteriole controls separ
ate capillary groups. These arterioles all had the same concentration
dependence to locally (by micropipette) applied norepinephrine (NE, 10
(-9) to 10(-3) mol/L), and 10(-9) mol/L NE did not induce diameter cha
nges when applied locally to individual vessels. However, 10(-9) mol/L
NE added to the tissue superfusate, or 5% added superfusate oxygen (a
lso locally subthreshold), each induced significant diameter changes (
both constrictions and dilations), in different branches, that were pr
esumably due to summation of individually subthreshold events that cha
nged the prevailing conditions at the point of observation. These sign
ificant diameter changes were related to the maximal diameter or to in
itial tone of the branches, but these changes occurred in different wa
ys for NE versus oxygen. With NE, the branch arterioles that constrict
ed (versus dilated) were significantly larger (maximal diameter, 22.3/-2.6 versus 15.9+/-2.1 mum) and had higher tone (fractional constrict
ion, 0.53+/-0.05 versus 0.63+/-0.05); with oxygen, those that constric
ted were the same size as those that dilated (maximal diameter, 28.6+/
-1.1 versus 30.5+/-2.7 mum), but constrictors had lower tone (fraction
al constriction, 0.49+/-0.04 versus 0.39+/-0.06). Both vessel diameter
and tone were themselves significantly dependent on the sequential br
anch position. In addition, the spatial position of the branch along t
he transverse arteriole modified the extent to which diameter or tone
influenced the responses; with NE, the arterioles that were located di
stally along the transverse arteriole dilated (axial distance versus r
esponse, y=0.0001x-0.05; F test on slope, P=0.01), yet with oxygen, th
e distal arterioles constricted (y=-0.0001x-0.02; P=0.03). Thus, this
study shows that the small arterioles that control capillary perfusion
are capable of responding differently from each other in a spatially
organized way and, further, that the spatial pattern of diameter chang
e is different when prevailing conditions (eg, local pressure/flow) ar
e altered b adrenergic versus metabolic means.