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 (So(2)) 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 So(2) levels based on microspectrophotometry data obtained by using 3 different optical filters and a cooled CCD camera. The So(2) images showed lower So(2) levels in arterioles close to their walls, and the So(2) levels in the paired venules showed higher So(2) levels close to the arterioles. There were capillaries that crossed the microvessels whose So(2) levels changed as they crossed the microvessels. The So(2) levels were lower close to the vessel wall than in the centerline level of the microvessels, and the highest So(2) levels in venules paralleling arterioles were skewed toward the arterial side. The So(2) images showed that the So(2) level in arterioles decreased after crossing venules, whereas the So(2) level in venules increased after crossing arterioles. Conclusions-Visualization of intravascular So(2) 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.