Minimally invasive, in vivo exploration of mouse small artery reactivity

The aim of the study was to investigate in vivo arterial reactivity in the mouse hind limb using Orthogonal Polarisation Spectral (OPS) imaging, which delivers high-contrast images of vascular beds by visualizing red blood cells. After minimal skin invasion of anesthetized mice, the OPS probe was placed on the hind limb continuously superfused with physiological saline solution. Then, the response of the saphenous artery (average luminal diameter 127 +/- 3 microm; n = 15) to topical application of increasing concentrations of acetylcholine or phenylephrine was examined. Mean carotid arterial blood pressure was unaffected during the experiment. The basal diameter decreased by 70% during exposure to phenylephrine (pD2: 5.65 +/- 0.08; n = 9), while acetylcholine augmented basal diameter up to 199% (pD2: 6.55 +/- 0.12; n = 6). Application of sodium nitroprusside did not further increase arterial diameter following acetylcholine exposure. After washing out, arterial luminal diameters returned to initial values. Second exposure to vasoactive agents demonstrated that changes in diameter were reproducible with time and not different between left and right saphenous arteries. Thus, OPS imaging is an in vivo dye-free, simple and minimally invasive approach, which provides unique information regarding the behavior of vascular network within conditions of cellular and physiological homeostasis.