Cigarette smoking is known to be one of the risk factors of subarachnoid hemorrhage (SAH), yet the precise mechanism remains to be proved. Based on the hypothesis that smoke components might enhance protease activity in the arterial wall, we examined the proteinase activities of plasma from smoke-extract-injected rats. Rats were injected intraperitoneally with smoke extract and the protease activity in the plasma was examined by zymography in the presence or the absence of proteinase inhibitors. Metalloproteinase activity was measured using a synthetic substrate. Proteolytic activities of 80- and 100-kDa against gelatin and collagen type I-V were induced 6 h after the injection. Inhibition of the activity by a metalloproteinase inhibitor but not by serine, cysteine or aspartic protease inhibitors suggested that the proteinases can be attributed to metalloproteinases. Cleavage activity in plasma toward a synthetic metalloproteinase substrate also increased within 24 h after the injection of the smoke extract. The results indicate that the induction of plasma metalloproteinase activity by smoke extract might account for the causal role of smoking in the development of SAH.

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