Expression of alpha-smooth muscle actin, TGF-β1 and TGF-β type II receptor during connective tissue contraction

Closure of rat mesenteric perforation is considered to occur by connective tissue contraction, a process that has been shown to be stimulated by transforming growth factor-β1. In the present study, we assessed the expression of alpha-smooth muscle actin during closure by quantitative- reverse transcription-polymerase chain reaction and in situ hybridization. The expression of transforming growth factor-β1 and transforming growth factor-β type II receptor was also estimated in mesenteric membranes and free peritoneal cells after wounding. A larger expression of alpha-smooth muscle actin was seen around the wound edges compared to unwounded tissue. Both alpha-smooth muscle actin and transforming growth factor-β type II receptor were expressed during Days 0, 3, 5, 7, and 10. The expression of alpha-smooth muscle actin on Day 5 was >100 times higher than on Day 0. Transforming growth factor-β1 was expressed in both membranes and free peritoneal cells of unoperated control animals but down-regulated after wounding, a finding that has not been reported previously. It reappeared on Days 7 and 10 in free peritoneal cells but not in perforated membranes. The enhanced expression of alpha-smooth muscle actin and down-regulation of transforming growth factor-β1 expression after wounding appears to be important phenomena in tissue contraction and repair.