Effects of fentanyl and its analogs on electric field-stimulated contractions of rat ileum
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Opiates inhibit electrically-stimulated contractions of isolated rat ileum acting on δ-receptors. We have examined effects of fentanyl and its three analogues on contractions of isolated rat ileum stimulated by electric field (20 V, 22 ms, 1 Hz). Fentanyl (from 10-9 M to 10-7 M) and trans-3-(carbomethoxy) fentanyl (from 10-7 M to 10-5 M) produced concentration-dependent decrease in amplitude of stimulated contractions, only fentanyl was about 40 times more potent. Cis-3-(methyl) fentanyl and Cis-3-(carbomethoxy) fentanyl did not affect stimulated contractions. Our study suggested that introduction of methyl and carbomethoxy moieties on position 3 of piperidine ring produced loss of fentanyl activity on δ-opioid receptors, cis-orientation being specially uafavourable.