Cardiovascular hyporesponsiveness in sepsis is associated with G-protein receptor kinase expression via a nitric oxide-dependent mechanism

Introduction

Septic shock is characterized by cardiac collapse and decreased peripheral resistance due to systemic resistance vessel dilatation, generally induced by large nitric oxide (NO). G-protein-coupled receptor (GPCR) kinases (GRKs), specific kinases interacting with GPCR proteins, induce receptor phosphorylation and thereby signal desensitization in the continuing agonist presence. Then, an increased expression of GRKs could augment adrenergic receptor desensitization and in turn reduce cardiovascular responses. Thus, we hypothesized that the hyporesponsiveness observed in sepsis could result from signal adrenergic receptor desensitization mediated by GRK2 via a NO-dependent mechanism.

Methods

C57Bl/6 mice were submitted to cecal ligation and puncture (CLP) surgery and sham-operated animals as controls. The cardiovascular responsiveness activity was evaluated in aorta rings or in cardiac ventricles. Aorta rings were contracted with phenylephrine (Phe; 1 μM), whereas ventricles were contracted with isoproterenol (Iso; 1 μM). The tissues responsiveness was evaluated 6, 12, and 24 hours after CLP surgery in the presence or absence of NO synthesis inhibitor (1400W; 100 μM; 30 min). GRK2 expression was analyzed on heart and aorta 6, 12, and 24 hours after CLP from sham, septic, and 1400W (1 mg/kg)-treated septic mice by immunofluorescence analysis. The procedures have been approved by the Animal Use Ethics Committees of UFSC (PP003).

Results

The vascular responsiveness to vasoconstrictor Phe was significantly reduced in aorta rings from septic mice evaluated 6 hours (55%), 12 hours (57%), and 24 hours (78%) after CLP. However, the 1400W incubation prevented this vascular hyporesponsiveness 6 and 12 hours after CLP. The cardiac responsiveness to Iso was significantly reduced in ventricles from septic mice evaluated 12 hours (73%) and 24 hours (88%) after CLP. Conversely, the 1400W incubation prevented this cardiac hyporesponsiveness 12 hours after CLP. Moreover, high expression of GRK was detected in aorta 6 hours (65%), 12 hours (70%), and 24 hours (88%), and heart of septic mice 12 hours (52%) and 24 hours (63%) after CLP. The 1400W treatment reduced the GRK high expression on the aorta (75%) and heart (79%) of septic mice.

Conclusions

Our findings identify that NO seems to activate GRK, which may induce adrenergic receptors' desensitization to agonists, contributing to severe cardiovascular hyporesponsiveness observed during septic shock. Therefore, the results suggest that GRK could be a new potential target to sepsis pharmacotherapy.