Ghrelin-induced gastroprotection against ischemia-reperfusion injury involves an activation of sensory afferent nerves and hyperemia mediated by nitric oxide.
Ghrelin has been recently identified as an endogenous ligand for growth hormone secretagogue receptor that regulates growth hormone secretion, increases appetite and contributes to energy homeostasis. Although this peptide is predominantly produced by the fasted stomach, little is known about its influence on the gastric mucosal integrity. The aim of the present study was (1) to investigate the effect of acylated ghrelin on the formation and healing of acute gastric mucosal lesions induced by ischemia-reperfusion and gastric mucosal blood flow in rats; (2) to analyse the effects of the deactivation of afferent sensory nerves with capsaicin and of the inhibition of nitric oxide (NO)-synthase by NG-nitro-l-arginine (l-NNA) on the ghrelin-induced protection; (3) to examine the influence of ghrelin on nuclear factor-kappa B (NF-kappaB) activation and on release of proinflammatory cytokines, such as tumor necrosis factor-alpha, (4) to assess the effect of ghrelin on the mRNA expression of constitutive nitric oxide synthase (cNOS), calcitonin gene related peptide (CGRP) and angiogenesis related proteins such as hypoxia inducible factor-1 alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF), and (5) to determine the effect of ischemia/reperfusion on the gastric mucosa expression of ghrelin in rats without and with administration of exogenous hormone. Wistar rats were exposed to 30 min of ischemia followed by 3 h of reperfusion. Ghrelin was administered in dose of 5, 10 or 20 mug/kg intraperitoneally (i.p.) 30 min prior exposure to ischemia/reperfusion and at 3 h after the end of ischemia, the mean lesion area was measured by planimetry and the changes in gastric blood flow were determined by hydrogen (H2)-gas clearance method. The healing of ischemia/reperfusion induced lesions was evaluated at 24 h or 6 days after the end of standard ischemia/reperfusion. The expression of cNOS, CGRP, HIF-1alpha, VEGF and ghrelin was evaluated by reverse transcription polymerase chain reaction or Western blot. Ghrelin significantly attenuated the ischemia/reperfusion-induced gastric lesions and accelerated the healing of these lesions while significantly raising the gastric blood flow. Deactivation of sensory nerves with capsaicin or inhibition of cNOS by L-NNA significantly attenuated the protective activity of ghrelin and accompanying increase in the GBF. Exogenous ghrelin significantly inhibited the activation of NF-kappaB and plasma TNF-alpha levels. The ghrelin-enhanced acceleration of healing of ischemia/perfusion induced lesions was accompanied by enhanced expression of mRNA for HIF-1alpha and by diminution of the ischemia/reperfusion induced increase in mRNA expression for TNF-alpha. We conclude that ghrelin exerts a potent protective action on the gastric mucosa and accelerates the healing of ischemia/reperfusion-induced lesions and these effects depend upon activation of sensory nerves, hyperemia mediated by NO, increased angiogenesis due to expression of YEGF and anti-inflammatory properties of this peptide.