The dopaminergic system modulates the endogenous opioid system in guinea-pig isolated ileal longitudinal muscle

The dopaminergic system modulates the endogenous opioid system in guinea-pig isolated ileal... The effects of the dopamine antagonists haloperidol and sultopride were investigated on the twitch response, evoked by 0.1 Hz stimulation of guinea-pig isolated ileal longitudinal muscle, and on the inhibition of the twitch response induced by 10 Hz stimulation (post-tetanic twitch inhibition) and by application of opioids. Both haloperidol and sultopride concentration-dependently inhibited the twitch response, with threshold concentrations of 2 and 50 μM, respectively, and could also shift the concentration-response curve for ACh-contraction to the right in a non-competitive manner. Haloperidol (1 μM) and sultopride (20 μM) increased post-tetanic twitch inhibition and this could be prevented by naloxone (100 nM). Twitch inhibition induced by morphine and dynorphin 1–13 was not affected by haloperidol (1 μM) or sultopride (20 μM). Prazosin (1 μM) and yohimbine (2 μM) did not affect either the twitch response or the post-tetanic twitch inhibition. These results suggest that dopamine receptors are involved in the modulation of the ileal opioid system, in such a manner as to diminish the release of endogenous opioids by tetanic stimulation. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Neuropharmacology Elsevier

The dopaminergic system modulates the endogenous opioid system in guinea-pig isolated ileal longitudinal muscle

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Publisher
Elsevier
Copyright
Copyright © 1995 Elsevier Ltd
ISSN
0028-3908
eISSN
1873-7064
DOI
10.1016/0028-3908(94)00166-P
Publisher site
See Article on Publisher Site

Abstract

The effects of the dopamine antagonists haloperidol and sultopride were investigated on the twitch response, evoked by 0.1 Hz stimulation of guinea-pig isolated ileal longitudinal muscle, and on the inhibition of the twitch response induced by 10 Hz stimulation (post-tetanic twitch inhibition) and by application of opioids. Both haloperidol and sultopride concentration-dependently inhibited the twitch response, with threshold concentrations of 2 and 50 μM, respectively, and could also shift the concentration-response curve for ACh-contraction to the right in a non-competitive manner. Haloperidol (1 μM) and sultopride (20 μM) increased post-tetanic twitch inhibition and this could be prevented by naloxone (100 nM). Twitch inhibition induced by morphine and dynorphin 1–13 was not affected by haloperidol (1 μM) or sultopride (20 μM). Prazosin (1 μM) and yohimbine (2 μM) did not affect either the twitch response or the post-tetanic twitch inhibition. These results suggest that dopamine receptors are involved in the modulation of the ileal opioid system, in such a manner as to diminish the release of endogenous opioids by tetanic stimulation.

Journal

NeuropharmacologyElsevier

Published: May 1, 1995

References

  • A comparison of in vitro and in vivo dopamine receptor antagonism produced by substituted benzamide drugs
    Jenner, P.; Elliot, P.N.C.; Clow, A.; Reavill, C.; Marsden, C.D.
  • The origin of acetylcholine released from guinea-pig intestine and longitudinal muscle strips
    Paton, W.D.M.; Zar, M.A.

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