Dynamics of GRK2 in the kidney: a putative mechanism for sepsis-associated kidney injury

Blockade of sympathetic ganglia improves vascular dysfunction in septic shock

Sepsis/septic shock activates the sympathetic nervous system (SNS) to deal with the infection stress. However, an imbalanced or maladaptive response due to excessive or uncontrolled activation characterizes autonomic dysfunction. Our hypothesis was that reducing this excessive activation of the autonomic nervous system would impact positively in sepsis. Using ganglionic blockers as a pharmacological approach, the main aim of the present report was to assess the role of ganglionic transmission in the vascular dysfunction associated with sepsis.Sepsis was induced in rats by cecal ligation and puncture (CLP). One hour after CLP surgery, rats were treated subcutaneously with hexamethonium (15 mg/kg; ganglionic blocker), pentolinium (5 mg/kg; a blocker with a higher selectivity for sympathetic ganglia compared to hexamethonium), or vehicle (PBS). Basal blood pressure and the response to adrenergic agonists were evaluated at 6 and 24 h after CLP surgery. Reactivity to vasoconstrictors, nitric oxide (NO) synthase 2 (NOS-2) expression, IL-1 and TNF plasma levels, and density of α1 adrenergic receptors were evaluated in the aorta 24 h after CLP.Septic shock resulted in hypotension and hyporesponsiveness to norepinephrine and phenylephrine, increased plasma cytokine levels and NOS-2 expression in the aorta, and decreased α1 receptor density in the same vessel. Pentolinium but not hexamethonium recovered responsiveness and α1 adrenergic receptor density in the aorta. Both blockers normalized the in vivo response to vasoconstrictors, and reduced plasma IL-1 and NOx levels and NOS-2 expression in the aorta.Blockade of ganglionic sympathetic transmission reduced the vascular dysfunction in experimental sepsis. This beneficial effect seems to be, at least in part, due to the preservation of α1 adrenergic receptor density and to reduced NOS-2 expression and may lead to adjuvant ways to treat human sepsis.

The role of nitric oxide in sepsis-associated kidney injury

Sepsis is one of the leading causes of acute kidney injury (AKI), and several mechanisms including microcirculatory alterations, oxidative stress, and endothelial cell dysfunction are involved. Nitric oxide (NO) is one of the common elements to all these mechanisms. Although all three nitric oxide synthase (NOS) isoforms are constitutively expressed within the kidneys, they contribute in different ways to nitrergic signaling. While the endothelial (eNOS) and neuronal (nNOS) isoforms are likely to be the main sources of NO under basal conditions and participate in the regulation of renal hemodynamics, the inducible isoform (iNOS) is dramatically increased in conditions such as sepsis. The overexpression of iNOS in the renal cortex causes a shunting of blood to this region, with consequent medullary ischemia in sepsis. Differences in the vascular reactivity among different vascular beds may also help to explain renal failure in this condition. While most of the vessels present vasoplegia and do not respond to vasoconstrictors, renal microcirculation behaves differently from nonrenal vascular beds, displaying similar constrictor responses in control and septic conditions. The selective inhibition of iNOS, without affecting other isoforms, has been described as the ideal scenario. However, iNOS is also constitutively expressed in the kidneys and the NO produced by this isoform is important for immune defense. In this sense, instead of a direct iNOS inhibition, targeting the NO effectors such as guanylate cyclase, potassium channels, peroxynitrite, and S-nitrosothiols, may be a more interesting approach in sepsis-AKI and further investigation is warranted.