Novel targets for sepsis-induced kidney injury: the glomerular arterioles and the sympathetic nervous system

Sepsis and septic shock are the most common causes of acute kidney injury (AKI) in the intensive care unit, and mortality remains high despite improvements in our ability to support vital organs. The lack of development of effective treatments is partly because there has been little advance in our understanding of the pathophysiology of septic AKI, owing to the difficulty in conducting experiments on critically ill patients and use of inappropriate experimental models. Recently, however, a number of new concepts have emerged that challenge existing dogma and give insights into the causes of AKI. Traditionally, renal ischaemia has been proposed as the main cause of AKI, but it is becoming apparent that in sepsis with a hyperdynamic circulation, the most common situation in septic patients, there is an increase or at least no decrease in renal blood flow. In this review, the possible role of changes in pre- and postglomerular resistance in setting the increased level of renal blood flow in the presence of a decreased glomerular filtration rate is discussed. New evidence also indicates that the increased sympathetic nerve activity that occurs in sepsis may contribute to the induction of organ failure. Experimental studies indicate that inhibition of central sympathetic outflow with α2-adrenoceptor agonists or treatment with β1-adrenoceptor antagonists might reduce mortality in experimental endotoxaemia and sepsis. The possibility that these beneficial actions are partly dependent on a reduction in the excessive cytokine release caused by marked and prolonged sympathetic activation is discussed.