Delta opioid receptors contribute to the cardiorespiratory effects of biphalin in anesthetized rats

Biphalin expresses almost equal affinity for μ- and δ-opioid receptors. the aim of this study was to delineate a possible role of δ-opioid receptors in the cardio-respiratory effects of systemic injection of biphalin in anesthetized,spontaneously breathing rats. in control animals,an intravenous bolus of biphalin (0.3 μmol/kg) evoked apnea,followed by a decreased breathing rate and increased tidal volume,hypotension and bradycardia. blockade of δ-opioid receptors with naltrindole (4.2 μmol/kg) significantly reduced the duration of apnea,slowdown of respiration,immediate post-challenge hypotension and bradycardia induced by biphalin administration. these results indicate that the activation of δ-opioid receptors adds to the depressive response produced by biphalin. copyright © 2011 by institute of pharmacology polish academy of sciences.