Effects of narcotic analgesics on contractions of the chick isolated, innervated oesophagus

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Abstract
The effects of the analgesics, morphine, diacetylmorphine, etorphine, methadone, pethidine, propoxyphene, pentazocine, cyclazocine and phenazocine were studied on contractions of the isolated innervated oesophagus of chicks. All of the analgesics depressed contractions of the oesophagus evoked by coaxial stimulation, the effect being greater the lower the frequency of stimulation. Tachyphylaxis and cross tachyphylaxis to and between the drugs developed rapidly. During the depressant effect on the electrically evoked contractions, responses to acetylcholine and 5-hydroxytryptamine were not depressed, except in the cases of pethidine, propoxyphene and pentazocine which depressed responses to acetylcholine. Nalorphine added during the depressant action antagonized the effects of morphine, diacetylmorphine, etorphine, methadone and phenazocine, partially antagonized those of pethidine and propoxyphene but did not antagonize those of pentazocine or cyclazocine.