Imaging of oxygen transfer among microvessels of rat cremaster muscle.

BACKGROUND The proximity of capillaries, arterioles, and venules provides complex spatial relationships that lead to oxygen transfer among microvessels. Although a conceptual image of complex oxygen transfer among microvessels has been hypothesized, in vivo mapping of oxygen saturation (SO2) levels in microvessels had never been performed. METHODS AND RESULTS The oxygen profile of the arterioles and venules of the rat cremaster muscle during normoxia and hypoxia was visualized by preparing pseudo-color images of SO2 levels based on microspectrophotometry data obtained by using 3 different optical filters and a cooled CCD camera. The SO2 images showed lower SO2 levels in arterioles close to their walls, and the SO2 levels in the paired venules showed higher SO2 levels close to the arterioles. There were capillaries that crossed the microvessels whose SO2 levels changed as they crossed the microvessels. The SO2 levels were lower close to the vessel wall than in the centerline level of the microvessels, and the highest SO2 levels in venules paralleling arterioles were skewed toward the arterial side. The SO2 images showed that the SO2 level in arterioles decreased after crossing venules, whereas the SO2 level in venules increased after crossing arterioles. CONCLUSIONS Visualization of intravascular SO2 levels suggested that oxygen is transferred between paired microvessels and between crossing microvessels in rat cremaster muscle. The possibility that oxygen is transported from some arterioles to venules and tissue through adjacent capillaries is proposed.