Opioid receptors in fast and slow skeletal muscles of normal and dystrophic mice

The density of beta-endorphin receptors and the proportions of fibres that expressed the receptors was assessed in fast extensor digitorum longus muscle and slow soleus muscles of normal and dystrophic mice using [125I]beta-endorphin and autoradiography. In the EDL the density was approximately 3.5 times higher and the proportion of labelled fibres approximately 2.6 times higher in dystrophic mice than normal mice. In the soleus the density was approximately 6.4 times higher and the proportion of labelled fibres approximately 1.5 times higher in the dystrophic mice than the normal mice. The receptors were of the delta-opioid subtype.