Systemic and local effects of endotoxin on canine gracilis muscle vascular conductance

To define the site and mechanism of action that endotoxin has on the peripheral vasculature, an in situ constant-flow double-canine gracilis muscle (GM) preparation was utilized. During systemic endotoxemia, one GM was innervated and the other was denervated during a 30-min intravenous infusion of 2 mg/kg endotoxin. Significantly increased vascular conductance (URP) in the denervated GM (106 +/- 26%) occurred compared with the innervated GM (50 +/- 7%), which suggests that decompensation is not totally dependent on neural depression. During local endotoxemia, with both GMs either intact or denervated, one GM was infused intra-arterially for 30 min with a dose of endotoxin calculated to provide a blood concentration similar to that achieved during systemic endotoxemia, whereas the other GM was infused with the vehicle. The URPs did not change significantly in either the saline or endotoxin GMs. Therefore, endotoxin does not act directly on peripheral vasculature or totally through depression of the autonomic nervous system. It apparently interacts with a systemically dependent mechanism to release a vasodepressor substance that is transported to the peripheral vasculature causing relaxation of vascular tone.