Myosin light chain kinase is necessary for post-shock mesenteric lymph drainage enhancement of vascular reactivity and calcium sensitivity in hemorrhagic-shocked rats

Y.P Zhang,Y.H Si,Z.G Zhao,C.Y Niu,L.M Zhang

doi:10.1590/1414-431x20132900

Y.P Zhang, Y.H Si + Show 3 more

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https://doi.org/10.1590/1414-431x20132900

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Abstract

Vascular hyporeactivity is an important factor in irreversible shock, and post-shock mesenteric lymph (PSML) blockade improves vascular reactivity after hemorrhagic shock. This study explored the possible involvement of myosin light chain kinase (MLCK) in PSML-mediated vascular hyporeactivity and calcium desensitization. Rats were divided into sham (n=12), shock (n=18), and shock+drainage (n=18) groups. A hemorrhagic shock model (40±2 mmHg, 3 h) was established in the shock and shock+drainage groups. PSML drainage was performed from 1 to 3 h from start of hypotension in shock+drainage rats. Levels of phospho-MLCK (p-MLCK) were determined in superior mesenteric artery (SMA) tissue, and the vascular reactivity to norepinephrine (NE) and sensitivity to Ca2+ were observed in SMA rings in an isolated organ perfusion system. p-MLCK was significantly decreased in the shock group compared with the sham group, but increased in the shock+drainage group compared with the shock group. Substance P (1 nM), an agonist of MLCK, significantly elevated the decreased contractile response of SMA rings to both NE and Ca2+ at various concentrations. Maximum contractility (Emax) in the shock group increased with NE (from 0.179±0.038 to 0.440±0.177 g/mg, P<0.05) and Ca2+ (from 0.515±0.043 to 0.646±0.096 g/mg, P<0.05). ML-7 (0.1 nM), an inhibitor of MLCK, reduced the increased vascular response to NE and Ca2+ at various concentrations in the shock+drainage group (from 0.744±0.187 to 0.570±0.143 g/mg in Emax for NE and from 0.729±0.037 to 0.645±0.056 g/mg in Emax for Ca2+, P<0.05). We conclude that MLCK is an important contributor to PSML drainage, enhancing vascular reactivity and calcium sensitivity in rats with hemorrhagic shock.

Highlights

Vascular hyporeactivity to vasoconstrictors occurs during sepsis and trauma
This study explored the possible involvement of myosin light chain kinase (MLCK) in post-shock mesenteric lymph (PSML)-mediated vascular hyporeactivity and calcium desensitization
Levels of phospho-MLCK (p-MLCK) were determined in superior mesenteric artery (SMA) tissue, and the vascular reactivity to norepinephrine (NE) and sensitivity to Ca2+ were observed in SMA rings in an isolated organ perfusion system. pMLCK was significantly decreased in the shock group compared with the sham group, but increased in the shock+drainage group compared with the shock group

Summary

Introduction

Vascular hyporeactivity to vasoconstrictors occurs during sepsis and trauma. Hemorrhage is the major underlying mechanism of microcirculation failure, refractory hypotension, no-reflow phenomenon and vital-organ hypoperfusion. A number of studies showed that receptor desensitization [2,3], hyperpolarization of membrane potential [4,5,6] and decreased sensitivity of contractile elements to Ca2+ in vascular smooth muscle cells (VSMCs) [7,8,9,10] all contribute to the development of vascular hyporeactivity. Findings from our laboratory suggested that mesenteric duct ligation and PSML drainage both improved the reactivity and calcium sensitivity of vascular rings (i.e., cross-sections) isolated from severely shocked rats [15]. In vitro experiments demonstrated that the mesenteric lymph harvested from 1-3 h after shock decreased the contractile activity and calcium sensitivity of normal vascular rings [15]. The mechanism by which the mesenteric lymph of severe shock conditions blunts vascular reactivity is not clear

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