Adrenocorticotropin reverses hemorrhagic shock in anesthetized rats through the rapid activation of a vagal anti-inflammatory pathway

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Abstract
Objective: Several melanocortin peptides have a prompt and sustained resuscitating effect in conditions of hemorrhagic shock. The transcription nuclear factor kB (NF-kB) triggers a potentially lethal systemic inflammatory response, with marked production of tumor necrosis factor-α (TNF-α), in hemorrhagic shock. Here we investigated whether the hemorrhagic shock reversal produced by the melanocortin ACTH-(1–24) (adrenocorticotropin) depends on the activation of the recently recognized, vagus nerve-mediated, brain “cholinergic anti-inflammatory pathway”. Methods and results: Anesthetized rats were stepwise bled until mean arterial pressure (MAP) atabilized at 20–25 mm Hg. The severe hypovolemia was incompatible with survival, and all saline-treated animals died within 30 min. In rats intravenously (i.v.) treated with ACTH-(1–24), neural efferent activity along vagus nerve (monitored by means of a standard system for extracellular recordings) was markedly increased, and the restoration of cardiovascular and respiratory functions was associated with blunted NF-kB activity and with decreased TNF-α mRNA liver content and TNF-α plasma levels. Bilateral cervical vagotomy, pretreatment with the melanocortin MC4 receptor antagonist HS014, atropine sulfate or chlorisondamine, but not with atropine methylbromide, prevented the life-saving effect of ACTH-(1–24) and the associated effects on NF-kB activity and TNF-α levels. HS014 and atropine sulfate prevented, too, the ACTH-(1–24)-induced increase in neural efferent vagal activity, and accelerated the evolution of shock in saline-treated rats. Conclusions: The present data show, for the first time, that the melanocortin ACTH-(1–24) suppresses the NF-kB-dependent systemic inflammatory response triggered by hemorrhage, and reverses shock condition, by brain activation (in real-time) of the “cholinergic anti-inflammatory pathway”, this pathway seeming to be melanocortin-dependent.