Abstract
Antibodies generated against small molecular weight substances such as drugs are being used to isolate and characterize biologically active agonists. A morphine-like compound can be extracted from brain of various species which has determinant groups that are recognized by specific morphine antibodies. It has a regional distribution which can be quantitated as immuno-equivalents. Immunological, chemical and chromatographic tests show great similatiries of the compound to morphine. This morphine-like compound has biological activity as it inhibits the electrically induced contractions both of the guinea pig ileum and mouse vas deferens but the inhibition is not reversed by naloxone or naltrexone.