Afferent vagal fibres and central cholinergic mechanisms are involved in the TRH-induced reversal of haemorrhagic shock

In a model of haemorrhagic shock causing the death of all saline-treated rats within 25.8 +/- 2.7 min after treatment, the intravenous injection of thyrotropin-releasing hormone tartrate (TRH-T) at the dose of 4 mg/kg induces a prompt and sustained increase of arterial pressure and pulse amplitude, with survival of all rats. Bilateral vagotomy, atropine sulphate (2 mg/kg intraperitoneally) and hemicholinium-3 (20 micrograms/rat intracerebroventricularly) partially prevent the TRH-T-induced shock reversal, whereas atropine methylbromide has no effect. These data indicate that afferent vagal fibres, brain cholinergic neurons and central muscarinic receptors play a role in the mechanism of the anti-shock effect of TRH-T.