Level of Sympathetically Mediated Arteriolar Control is Inversely Dependent on Arteriolar Segment Length in Rat Gluteus Maximus Microvascular Networks

The sympathetic nervous system (SNS) releases neuropeptide Y (NPY, acting on Y1‐receptors, Y1R) and norepinephrine (NE, acting on α‐adrenoreceptors) that constrict skeletal muscle arterioles to modulate their resistance and blood flow. We recently reported that αR and Y1R control displayed topological dependency; in that α‐adrenoreceptor control was greatest at proximal vessels (i.e., 1st and 2nd order arterioles), while NPY mediated effects were greatest on distal vessels, closest to capillaries (i.e., 4th and 5th order arterioles). In spite of this, we noted significant variability in the modulation of sister arterioles of differing segment lengths at bifurcations of the same order. Therefore, in the current study we hypothesized that SNS modulation would be inversely dependent on arteriolar segment length. Intravital video‐microscopy was performed on the rat gluteus maximus muscle and arteriolar lengths and constrictor responses to phenylephrine (PE, 10‐9M to 10‐4M, α1R agonist) and NPY (10‐13M to 10‐9M) were recorded (n=7 rats/group) and grouped with respect to vessel order (2nd order to 5th order). Plots were curve fitted (exponential decay) and goodness of fit (R2) values were evaluated. We found strong relationships (R2 = 0.8 to 0.99) between arteriolar lengths and the levels of sympathetic constriction for all conditions. These data highlight the need for considering microvascular geometry/topology when interpreting data in studies of microvascular control. NSERC