Effects of metaphit, a proposed phencyclidine receptor acylator, on catalepsy in pigeons

Metaphit, a derivative of phencyclidine (PCP), irreversibly binds to PCP sites in rat brain homogenates. PCP-induced catalepsy in pigeons, which is a pharmacologically specific and stereoselective phenomenon, was used to study pharmacological consequences of the proposed covalent bonding of metaphit to PCP sites. Metaphit pretreatment increased the cataleptic effects induced by cumulative doses of PCP-type drugs (i.e., PCP, ketamine and m-amino PCP) and of drugs that have PCP-like actions (i.e., dexoxadrol, LY 154716 and cyclazocine). Metaphit did not affect pentobarbital-induced loss of righting, head-drop and eye closure. Metaphit itself induced a PCP-like catalepsy. Isobolographic analysis of the interactions between metaphit and PCP-like drugs suggested that metaphit potentiated the catalepsy-inducing effects of these drugs. The possibility that metaphit exerts its potentiating effects by inhibition of PCP biotransformation was evaluated by measuring plasma and brain concentrations of PCP after pretreatment with either metaphit or SKF-525A, an inhibitor of the enzyme systems involved in PCP biotransformation. SKF-525A, but not metaphit, increased brain levels of PCP. The results suggest that metaphit acts not as an antagonist of PCP but as a less-potent, long-acting, specific PCP-like agonist. Potentiation by metaphit of the cataleptic effects of chemically diverse drugs with PCP-like actions does not appear to be based on inhibition of the enzyme systems involved in metabolism of those drugs.