An analysis of normeperidine's contribution to the rate-decreasing effects of meperidine.

The effects of normeperidine (1-17.5 mg/kg) alone and in the presence of naloxone (1 and 10 mg/kg) were studied in pigeons responding under a multiple fixed-ratio 30 response, fixed-interval 5-min schedule of food presentation. Naloxone only potentiated the rate-decreasing effects of normeperidine. The effects of meperidine also were studied after pretreatment with SKF-525A (25 and 50 mg/kg), an inhibitor of drug metabolism. SKF-525A had no effects on responding when administered alone, but it potentiated the rate-decreasing effects of meperidine. It was concluded that meperidine's rate-decreasing effects cannot be due to normeperidine, the metabolite, but rather that both of these drugs have non-narcotic actions which produce decreases in schedule-controlled responding.