Background. In the rat, there is a significantly greater blood flow response to wounding at the back, a site perfused mainly by small capillaries, than at the paw, which has a much higher density of arterioles and venules. Materials and methods. We characterized the microvascular composition of wounds at the two skin sites in 11 Wistar Kyoto rats using a quantitative imaging program. Blood flow was compared using laser Doppler technology. Results. Prior to wounding, skin blood flow was much greater at the paw (7.1 ± 0.5 ml 100 g tissue -1 min -1) than at the back (2.1 ± 0.1 ml 100 g tissue -1 min -1, P <0.01) at baseline. Seven days after wounding, blood flow both at the center (8.3 ± 1.4 ml 100 g tissue -1 min - 1) and at the perimeter of the back wound (4.1 ± 0.5 ml 100 g tissue -1 min -1) had increased substantially. In contrast, skin blood flow at the perimeter of the paw wound had increased moderately (12.7 ± 2.0 ml 100 g tissue -1 min -1), but there was no change at the center of the wound (6.9 ± 0.9 ml 100 g tissue -1 min -1). There were three times more microvessels per mm 2 at the paw site (39.3 ± 3.6) than at the back (13.1 ± 1.5) prior to wounding. The wound granulation tissue was very vascular; the numerical density of vessels was identical at back (166 ± 9) and at paw (154 ± 6). Despite the marked increase in blood flow at the perimeter of the back wound, there was no difference in the microvascular density (15.2 ± 1.4) compared to baseline, nor was there a difference at the paw perimeter (39.4 ± 3.6) compared to baseline. Conclusions. This study demonstrates that the microvascular constitutions of granulation tissues at the paw and back are identical. Thus, the rise in flow at the back wound and reduction in flow at the paw wound are entirely consistent with similar microvascular compositions of these two sites. Yet, there is increased flow at the back wound perimeter where there is no significant change in microvascular constitution compared to unwounded skin. Therefore, a microvascular structure no different from that prior to wounding functions very differently after wounding. Clearly vasoregulatory factors impact on the wound to modify flow through the microvascular network.
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