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Papers of the Week

Papers: 15 May 2021 - 21 May 2021

Animal Studies, Pharmacology/Drug Development

2021 May 14

J Pharmacol Exp Ther

Oxytocin receptor activation rescues opioid-induced respiratory depression by systemic fentanyl in the rat.


Opioid overdose intervention by naloxone, a high affinity receptor antagonist, reverses opioid-induced respiratory depression (OIRD) and analgesia by displacing opioids. Systemic naloxone stimulates release of the hypothalamic neuropeptide oxytocin, which has analgesic properties and participates in cardiorespiratory homeostasis. To test the hypothesis that oxytocin can reverse OIRD, we assessed the rescue potential of graded doses (0, 0.1, 2, 5, 10, 50 nmol/kg, i.v) of oxytocin to counter fentanyl (60 nmol/kg, i.v.)-induced depression of neural inspiration indexed by recording phrenic nerve activity (PNA) in anesthetized (urethane/α-chloralose), vagotomized, and artificially ventilated rats. Oxytocin dose-dependently rescued fentanyl OIRD by almost immediately reversing PNA burst arrest (=0.0057) and restoring baseline burst frequency (=0.0016) and amplitude (=0.0025) at low, but not high doses, resulting in inverted bell-shaped dose-response curves. Oxytocin receptor antagonism (40 nmol/kg, i.v.) prevented oxytocin reversal of OIRD (Arrest: =0.0066, Frequency: =0.0207, Amplitude: =0.0022). Vasopressin 1A receptor (V1aR) antagonism restored high-dose oxytocin efficacy to rescue OIRD (=0.0170 – <0.0001), resulting in classic sigmoidal dose-response curves, and prevented (=0.0135) transient hypertension from V1aR cross-activation (=0.0275). Alone, vasopressin (5 nmol/kg, i.v.) failed to reverse fentanyl respiratory arrest (=0.6184). The non-peptide oxytocin receptor agonist WAY-267464 (75 nmol/kg, i.v.), which has V1aR antagonist properties, quickly reversed fentanyl OIRD (<0.0001), with rapid recovery of PNA frequency (=0.0011) and amplitude (=0.0044) without adverse hemodynamic consequences (=0.9991). Findings indicate that peptide and non-peptide agonist activation of oxytocin receptors without V1aR cross-activation rescues fentanyl OIRD. Oxytocin receptor agonists could be lifesaving resuscitation agents that enhance rather than interrupt opioid analgesia. Oxytocin receptor activation produces analgesia. Here, we demonstrate that activation by the FDA-approved agonist oxytocin and the non-peptide partial agonist WAY-267464 can each reverse fentanyl cardiorespiratory depression. Selective targeting of oxytocin receptors for resuscitation from opioid overdose, alone or in combination with an opioid antagonist, could eliminate or attenuate negative side effects associated with traditional opioid receptor antagonism.