title: Effect of contrast media on radioimmunoassay of beta-endorphin in cerebrospinal fluid.
abstract: An effect of metrizamide, a contrast medium, on results of beta-endorphin radioimmunoassay was examined. We found that 1, 5, and 10 microL of the medium added to 100 microL of standard containing 0 to 500 pg of beta-endorphin shifted the standard curve to the left in proportion to the metrizamide concentration. Three other contrast media showed a similar effect at low concentrations of beta-endorphin. This effect of contrast media artificially increased results in radioimmunoassay of beta-endorphin in cerebrospinal fluid, the mean overestimate being 121.9% (range, 0 to 435%). For plasma samples, this effect of contrast media resulted in an average 11.7% overestimate of beta-endorphin (range, -16% to 41%). These observations bring into question the validity of a previous suggestion that an increase in beta-endorphin in cerebrospinal fluid after intracerebral electrical stimulation is the mechanism for stimulation-produced analgesia.
mesh_terms: D003287:Contrast Media / Q000134:cerebrospinal fluid*; D004723:Endorphins / Q000134:cerebrospinal fluid*; D005189:False Positive Reactions; D006801:Humans; D011863:Radioimmunoassay; D001615:beta-Endorphin
chemical_list: D003287:Contrast Media; D004723:Endorphins; D001615:beta-Endorphin