Mechanism of quasi-morphine withdrawal behaviour induced by methylxanthines

Of 7 phosphodiesterase inhibitors tested for ability to induce a quasi-morphine withdrawal syndrome (QMWS) in opiate-naive rats, five were effective in a dose-related way. These, in descending order of potency, were IBMX, ICI-63197, RO-201724, theophylline and caffeine. Their potencies in inducing a QMWS correlated significantly (P less than 0.05) with those in inhibiting low Km cyclic AMP phosphodiesterase of rat brain homogenate. There was no correlation with potencies in inhibiting cyclic GMP phosphodiesterase.