The possible role of dynorphin in the control of gut function was explored using longitudinal muscle-myenteric plexus preparations of the guinea pig ileum. Dynorphin-(1-130 as well as other endorphins, μ or k opioid alkaloids antagonized in a dose-dependent fashion the isometric contractions caused by neurotensin. Ethylketocyclazocine and dynorphin-(1-13) were found to be potent inhibitors of the neurotensin-induced excitatory response, having IC50s of about 1 and 5 nM respectively; ketocyclazocine, normorphine and leucine enkephalin also inhibited the contractile effect of neurotensin but at concentrations 2, 30 and 400 times that of dynorphin (1-13).
Bibliographical noteFunding Information:
This investigation was partially supported by NIDA grants DA 01696 and DA 00037. Y.X. Zhu is a visiting scholar from the People's Republic of China with a fellowship from the World Health Organization. We thank Dr. E.T. lwamoto for the samples of ketocyclazoclnes. Also we wish to thank L'Inglessina Carnes for secretarial assistance.