RhoA/ROK and NO contribute to vascular hyporeactivity in endotoxaemic rats

Abstract

Hypotension and vascular hyporeactivity are significant characteristics of septic shock. The RhoA/Rho-kinase (RhoA/ROK) pathway is a major target for regulating calcium sensitivity of agonist-induced contraction. Here, we investigated the role of RhoA/ROK pathway in vascular hyporeactivity in endotoxaemic animals. Male Wistar rats were intravenously infused with E. coli lipopolysaccharide (LPS, 10 mg/kg) to induce endotoxaemia. Experimental animals were assigned to five groups: (i) 6 h after saline (Control); (ii) 1 h after LPS (LPS1h); (iii) 2 h after LPS (LPS2h); (iv) 4 h after LPS (LPS4h); (v) 6 h after LPS (LPS6h). LPS1h and LPS2h were regarded as early endotoxaemia, whereas LPS4h and LPS6h were regarded as late endotoxaemia. Results showed that LPS induced a biphasic hypotension and sustained vascular hyporeactivity in vivo, and this hyporeactivity only occurred in late endotoxaemia ex vivo. Meanwhile, the aortic inducible nitric oxide (NO) synthase expression and the serum NO level were time-dependently increased after LPS. However, the aortic RhoA activity and myosin phosphatase targeting subunit 1 phosphorylation were increased in early endotoxaemia and this vascular reactivity was inhibited by ROK inhibitor, Y27632. In addition, the plasma bradykinin level was increased at 15 min and aortic endothelial NO synthase expression was increased 1 h after LPS. In conclusion, an increased RhoA activity may compensate vascular hyporeactivity in early endotoxaemia, whereas in late endotoxaemia, the large amount of NO produced causes inhibition of RhoA activity leading to vascular hyporeactivity in vivo and ex vivo.