FINAL ACCEPTED VERSION Upregulation of cardiovascular ghrelin receptor occurs in the hyperdynamic phase of sepsis

Ghrelin, a newly identified endogenous ligand for growth hormone secretagogue receptor 1a (GHSR-1a, i.e., ghrelin receptor), was recently demonstrated to be a potent vasoactive peptide. Although sepsis is characterized by an early, hyperdynamic phase, it remains unknown whether ghrelin or GHSR-1a plays a role in the cardiovascular response to sepsis. To determine this, polymicrobial sepsis was induced by cecal ligation and puncture (CLP) in male adult rats. At 5 h (i.e., early sepsis) or 20 h (i.e., late sepsis) after CLP, blood and tissue samples were collected. Ghrelin levels, ghrelin and GHSR-1a mRNA expression were assessed by RIA and RT-PCR, respectively. In addition, GHSR-1a protein levels in the aorta, heart and small intestine were determined by Western blotting. The vascular response to ghrelin was determined by using an isolated gut preparation. A primary rat aortic smooth muscle cell culture (SMC) was used to determine the effects of lipopolysaccharide (LPS) on GHSR-1a expression. The results indicate that although ghrelin levels decreased at both early and late stages of sepsis, its receptor was markedly elevated in early sepsis. Moreover, ghrelin-induced relaxation in resistance blood vessels of the isolated small intestine increased significantly during the early stage of sepsis, but was not altered in the late stage of sepsis. Furthermore, GHSR-1a expression in SMC was significantly increased at both mRNA and protein levels with as little as 10 ng/ml LPS stimulation. These results demonstrate that GHSR-1a expression is upregulated and vascular sensitivity to ghrelin stimulation is increased in the hyperdynamic phase of sepsis.