Fig. 1.
Experimental protocol for evaluating diameters and reactivity in microvascular resistance networks of mouse gluteus maximus muscle (GM). Once anesthesia was induced, surgery required ∼1 h, followed by 30 min equilibration (E30'). Evaluation of constriction in respective vessel branch orders [feed artery (FA), first-order arteriole (1A), second-order arteriole (2A), third-order arteriole (3A)] during equilibration with 21% oxygen (O2) in the superfusion solution required ∼15 min. The superfusion was then re-equilibrated with 0% O2 for another 20 min before proceeding (E 20′). Cumulative concentration-response relationships (10−9 to 10−5 M) required ∼40 min to evaluate each agonist [phenylephrine (PE), UK 14304, ACh] across vessel branch orders followed by 30 min washout and equilibration (E 30′) with control physiological salt solution to restore spontaneous vasomotor tone. Each preparation experienced all stimuli with the order of agonist treatment and the sequence in which vessel branch orders were studied randomized across preparations. An entire experiment required 5 to 6 h to complete. ID, internal diameter; IDrest, resting ID; IDmax, maximal ID to 10−4 M sodium nitroprusside (SNP) or 10−5 M ACh, whichever is greater; IDO2, ID during 21% O2; IDssr = steady-state response ID.