Beta-endorphin suppression of acute morphine abstinence in morphine dependent monkeys: effective given intraventricularly but ineffective given intravenously.

Six female adult Macaca mulatta monkeys were made dependent upon morphine sulfate and were implanted with a chronic indwelling needle in the lateral ventricle of the brain for sterile intraventricular injections. Both beta-endorphin and morphine, in a dose dependent manner given intraventricularly suppressed the signs of 14 hour acute morphine abstinence. On a molar basis, beta-endorphin was more active than morphine in suppressing the signs of morphine abstinence. When given intravenously in much larger doses, beta-endorphin was ineffective in contrast to morphine which was effective in suppressing abstinence.