Quantification of the Inflammatory Reaction and Collagen Accumulation in an Experimental Model of Open Wounds in the Rat: A Methodological Study

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Abstract
An experimental model for studying the early healing of open wounds in the rat is described. With this model. exudate is easily collected, a standardized granulation tissue is achieved at different post-wounding time intervals and local treatment of the wounds is possible. The model involves the use of stainless steel rings with covers, fastened to the edges of two circular full-thickness open wounds, one on each side of the animal's back in the thoracic region. Blood flow and water content of the granulation tissue were determined acutely 3, 5, 7 and 10 days after wounding. The collagen accumulation in the granulation tissue was assessed by the amount of hydroxyproline, at the same time intervals. The amount of exudate which accumulated in the chamber was measured daily. Blood flow in the granulation tissue, as measured by radioactive microspheres, reached a maximum of 947 ml · min-1 · (100 g dry weight)-1 7 days after wounding The water content, as assessed by freeze-drying, also reached its peak on the 7th day (5.5 ml · (g dry weight)-1). Changes in water content were found to be due to changes in interstitial fluid volume, as studied by 59Fe-labelled erythrocytes and 51Cr-EDTA. The amount of hydroxy-proline in the granulation tissue increased from 22 μg-(mg dry weight)-1 on day 3 to 37 μg· (mg dry weight)-1 on day 10. Exudation increased to 28 μl·h-1 · cm2-1 on day 4 and then declined. The results suggest that the inflammatory reaction, expressed as alterations in blood flow and water content, reaches a maximum on day 7 after wounding. The data also demonstrate a continuous increase in the collagen content of the granulation tissue during the 10-day period of observation. In addition, exudation was found to reach a peak on the 4th to 5th day, and then declined.