Interaction between dihydropyridine calcium antagonists and morphine on the brain biogenic amines

1. Nifedipine, nimodipine or nisoldipine, were i.p. administered to normal, morphine treated or morphine abstinent rats in order to study their effects on brain biogenic amines and metabolites. 2. On various brain areas, the compounds studied decreased DOPAC and/or HVA levels, but increased 5-HIAA levels, leaving unchanged DA and 5-HT contents. 3. This suggested that DA turnover was decreased, whereas 5-HT turnover was increased, by inhibition of neuronal calcium influx. 4. Calcium antagonists: (a) further enhanced the effect of morphine on 5-HT turnover, which may involve an indirect inhibition of voltage sensitive calcium channels; (b) antagonized the effects of morphine on DA turnover, which are believed to be mediated by disinhibition of dopaminergic pathways. 5. The dihydropyridine calcium antagonists showed some differences in regional specificity and in profile of effects.