Role of central and peripheral opiate receptors in the effects of fentanyl on analgesia, ventilation and arterial blood-gas chemistry in conscious rats.

•NLXmi is a peripherally restricted μ-OR antagonist.•The analgesic effects of fentanyl involve peripheral μ-ORs that are sensitive to blockade by NLXmi.•The ventilatory depressant effects of fentanyl involve peripheral μ-ORs that are sensitive to NLXmi.•NLXmi prevents the negative effects of fentanyl on ABG chemistry.•NLXmi does the above by blocking fentanyl effects on tidal volume and A-a gradient.