Ghrelin improves tissue perfusion in severe sepsis via downregulation of endothelin-1.

OBJECTIVES: Severe sepsis is associated with increased total peripheral resistance (TPR) and decreased organ blood flow, in which endothelin-1 (ET-1) plays an important role. Plasma levels of ghrelin, a newly-identified endogenous ligand for growth hormone secretagogue receptor and a potent vasodilatory peptide, are significantly reduced in sepsis. Ghrelin downregulation heralds the hypodynamic response in severe sepsis. Therefore, we hypothesized that the administration of exogenous ghrelin improves organ blood flow by downregulation of ET-1 under such conditions. METHODS: Male adult Sprague-Dawley rats were subjected to sepsis by cecal ligation and puncture (CLP). At 5 h post-CLP, a bolus intravenous injection of 2 nmol ghrelin was followed by a continuous infusion of 12 nmol ghrelin via a primed mini-pump over 15 h. At 20 h post-CLP (i.e., severe sepsis), cardiac output (CO), stroke volume (SV), TPR, and organ blood flow were measured using (141)Ce-microspheres. Plasma ET-1 levels and preproET-1 gene expression in the liver, small intestine, and kidneys were measured by ELISA and RT-PCR, respectively. The direct effect of ghrelin on ET-1 production was studied using cultured human umbilical vein endothelial cells (HUVECs) treated with tumor necrosis factor-alpha (TNF-alpha). RESULTS: Ghrelin administration reduced TPR, increased CO, SV, and organ blood flow, downregulated preproET-1 gene expression, and decreased plasma levels of ET-1 in sepsis. Ghrelin inhibited TNF-alpha-induced ET-1 release from HUVECs in a dose-dependent manner. Moreover, ghrelin inhibited TNF-alpha-induced activation of nuclear factor-kappaB (NF-kappaB) in HUVECs. CONCLUSIONS: The improvement of tissue perfusion by ghrelin in severe sepsis appears to be mediated by downregulation of ET-1 involving a NF-kappaB-dependent pathway.

Increased gut-derived norepinephrine release in sepsis: up-regulation of intestinal tyrosine hydroxylase.

Studies have shown that increased gut-derived norepinephrine (NE) release plays an important role in producing hepatocellular dysfunction at the early stage of sepsis. Although the gut has been demonstrated to be the major source of NE in sepsis, it remains unknown whether the increased NE is associated with up-regulation of intestinal NE biosynthesis enzymes such as tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH). To determine this, adult male rats were subjected to sepsis by cecal ligation and puncture (CLP) followed by fluid resuscitation. Small intestinal samples were harvested at 2 h (i.e., early sepsis) or 20 h (late sepsis) after CLP or sham-operation. Protein levels of TH and DBH were determined by Western blot analysis and immunohistochemistry. Their gene expression was assessed by RT-PCR technique. The results indicate that intestinal TH protein levels increased significantly at 2 and 20 h after CLP, while DBH was not altered under such conditions. Immunohistochemical examination shows that both TH and DBH were located in intestinal sympathetic nerve fibers and TH staining was markedly increased in septic animals. TH gene expression increased significantly at 2 h but not at 20 h after CLP, while DBH gene expression was not altered in sepsis. Thus, the increased TH gene and protein expression appears to be responsible for the increased gut-derived NE in sepsis.