The effect of nifedipine and verapamil on nicotine-induced antinociception in rats

We examined the modulatory effect of nifedipine (NIF, 0.04, 2, 5 and 15 mg/kg i.p.) and verapamil (VER, 2.5 and 10 mg/kg s.c.) on nicotine-induced antinociception in male rats, employing the tail-flick (TF) test. All rats were divided according to their responses to nicotine (1 mg/kg s.c.) alone, and classified as responders and nonresponders; both types were used. Both tested drugs were injected simultaneously with nicotine (NIC). In responders, NIC (1 mg/kg s.c.) alone produced a ceiling TF latency (15 sec) within 2.5 min lasting for 2.5 - 7.5 min. NIF, at the dose of 15 mg/kg i.p., prolonged this effect up to 40-50 min. Lower doses (5, 2 and 0.04 mg/kg) were not effective. VER in either dose did not prolong NIC-induced antinociception. In nonresponders, NIF also potentiated NIC-induced antinociception, and this effect appeared to be dose-related, lasting from 10 up to 40 min. VER was ineffective in either dose. These data support our hypothesis that calcium is involved, at least in part, in nicotine-induced antinociception. The potential risk for smoking patients treated with NIF is discussed.