beta-Endorphin: characteristics of binding sites in rabbit spinal cord.

The interaction of human beta-endorphin with binding sites in rabbit spinal cord has been characterized. The stereospecific high-affinity binding sites are concentrated in the dorsal half of the spinal cord. Scatchard analysis of the binding data shows heterogeneity of the binding sites that can be resolved into two populations with apparent dissociation constants of 3.0 (+/-2.0) X 10(-10) and 3.3 (+/- 0.5) X 10(-9) M. Sodium ions decrease the binding of human beta-endorphin to spinal cord to the same extent as found in rat brain. The ability of several opiates and opioid peptides to inhibit the binding of human beta-endorphin is also presented.