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The rat and mouse mesenteries consist of an array of thin, mesenchymally derived, connective tissue membranes. Perforations of rat membranes heal by closure within a week and the perforated rat mesentery has earlier been shown to be a very suitable model of true connective tissue repair. In the present study, the closure of perforations in the rat was studied by light and transmission electron microscopy as well as confocal microscopy after actin staining with phallacidin in order to better understand the cellular mechanisms of healing in this model. The healing of different sized mesenteric perforations was also quantitatively assessed and compared in rats and mice. Closure occurred rapidly between Days 5 and 7 in rats, the velocity of healing being dependent on the size of the wounds. During closure, fibroblasts close to the wound margin ultrastructurally showed long slender cytoplasmic processes that contained actin filaments as shown by fluorescence confocal microscopy. In mice, larger perforations of mesenteries decreased in size during the 3-week observation period, but very seldom closed completely. In conclusion, the data gathered now and earlier indicate that a contraction phenomenon is of major importance in the closure of rat mesenteric perforations. Until now, good models for genuine connective tissue contraction have been lacking and it is suggested that the perforated rat mesentery may be used as such a model system in the future. The finding that mouse mesenteric perforations normally do not heal will make comparative studies intriguing, but it also indicates basic differences between rats and mice with respect to connective tissue repair mechanisms. more...

Streptozotocin-induced diabetes mellitus is known to impair connective tissue repair in the perforated rat mesentery. The aim of the present investigation was to study quantitatively by morphometrical techniques the influence of diabetes on some aspects of the cellular ultrastructure related to connective tissue contraction in such healing. The cellular volume density increased significantly with time, presumably as a consequence of disappearance of interstitial edema. No difference was found in the amount of healing tissue formed between controls and diabetics. The surface volume density of the plasma membrane was significantly higher in control animals on Days 1-10, indicating an increased number of cellular protrusions and spikes which relate to the motility of the cells. The volume density of contractile filaments did not differ between controls and diabetics. The results suggest a reduced surface density of plasma membrane in diabetic cells, a finding which is compatible with reduced wound contraction in diabetes. more...