Functional coordination of the spread of vasodilations through skeletal muscle microvasculature: implications for blood flow control

Aim We sought to understand the integrated vascular response to muscle contraction by determining how different branch orders of the terminal microvascular network respond to stimulation using a KATP channel opener pinacidil (PIN) as a muscle contraction mimetic. Methods Using the blood perfused, hamster cremaster preparation in situ, we locally micropipette-applied 10(-5) M PIN on the capillaries, Branch arteriole (third order, two branch orders up from the capillaries) and transverse arterioles (TA) (second order, three branch orders up from the capillaries) and observed different branch orders of the microvasculature to determine where the localized vasodilation spread throughout the terminal microvascular network. Results We observed that PIN stimulation of capillaries caused associated upstream vasodilation of the module inflow arteriole (MI) (fourth order, the terminal arteriole) (2.1 +/- 0.4 mu m), the associate Branch (1.4 +/- 0.5 mu m) and in the upstream direction on the TA (2.1 +/- 0.5 mu m). Vasodilation did not occur in all MIs (-0.2 +/- 0.2 mu m) from the vasodilated branch and did not go downstream on the TA (0.7 +/- 0.4 mu m). Branch stimulation caused upstream TA (3.3 +/- 1.0 mu m) and upstream Branch (1.7 +/- 0.3 mu m) vasodilation but not downstream TA (1.5 +/- 0.6 mu m) or downstream Branch (0.2 +/- 0.3 mu m) vasodilation. TA stimulation caused conducted responses in both directions and into all associated arteriolar Branches and MIs. Conclusions The spread of the conducted response is dependent on the vascular branch order stimulated: capillary stimulation was most specific in its direction and TA stimulation was the least specific. Our data indicate that vascular branch order is important in determining the vascular response needed to direct blood flow to contracting skeletal muscle cells.