Hydrogen sulphide induces μ opioid receptor-dependent analgesia in a rodent model of visceral pain

BACKGROUND: Hydrogen sulphide (H(2)S) is a gaseous neuro-mediator that exerts analgesic effects in rodent models of visceral pain by activating K(ATP )channels. A body of evidence support the notion that K(ATP )channels interact with endogenous opioids. Whether H(2)S-induced analgesia involves opioid receptors is unknown. METHODS: The perception of painful sensation induced by colorectal distension (CRD) in conscious rats was measured by assessing the abdominal withdrawal reflex. The contribution of opioid receptors to H(2)S-induced analgesia was investigated by administering rats with selective μ, κ and δ opioid receptor antagonists and antisenses. To investigate whether H(2)S causes μ opioid receptor (MOR) transactivation, the neuronal like cells SKNMCs were challenged with H(2)S in the presence of MOR agonist (DAMGO) or antagonist (CTAP). MOR activation and phosphorylation, its association to β arrestin and internalization were measured. RESULTS: H(2)S exerted a potent analgesic effects on CRD-induced pain. H(2)S-induced analgesia required the activation of the opioid system. By pharmacological and molecular analyses, a robust inhibition of H(2)S-induced analgesia was observed in response to central administration of CTAP and MOR antisense, while κ and δ receptors were less involved. H(2)S caused MOR transactivation and internalization in SKNMCs by a mechanism that required AKT phosphorylation. MOR transactivation was inhibited by LY294002, a PI3K inhibitor, and glibenclamide, a K(ATP )channels blocker. CONCLUSIONS: This study provides pharmacological and molecular evidence that antinociception exerted by H(2)S in a rodent model of visceral pain is modulated by the transactivation of MOR. This observation provides support for development of new pharmacological approaches to visceral pain.