Plasma B-endorphin levels in patients with self-injurious behavior and stereotypy.

B-endorphin and cortisol concentrations were examined in the plasma of mentally retarded patients who displayed symptoms of self-injurious behavior (SIB) (n = 9), stereotypy (n = 17), or SIB plus stereotypy (n = 14). Morning and evening samples were compared with a matched patient control group (n = 13) and a group of nonretarded controls (n = 17). Compared with nonretarded controls, the retarded control group had significantly lower b-endorphin concentrations for the morning sample and nonsignificantly lower concentrations for the evening sample. The combined patient groups had lower b-endorphin levels than did nonretarded controls for both samples. Patients with SIB and stereotypy had significantly higher morning levels of b-endorphin than the retarded controls. The evening levels of the SIB plus stereotypy group also were higher than retarded controls but were not significant. Levels in the SIB and stereotypy group were slightly elevated compared with retarded controls. Cortisol levels were identical for all groups. B-endorphin and cortisol significantly covaried for the nonretarded controls but not the patients. Results indicated that compared to a matched control group, patients with SIB plus stereotypy have elevated b-endorphin plasma.