Yohimbine reduces morphine tolerance in guinea-pig ileum |
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Authors: | L F Alguacil C Alamo C Santos E Cuenca |
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Institution: | 1. Division of Veterinary Pharmacology and Toxicology, Indian Veterinary Research Institute, Izatnagar-243 122, Bareilly, UP, India;2. Division of Veterinary Pathology, Indian Veterinary Research Institute, Izatnagar-243 122, Bareilly, UP, India;3. CADRAD, Indian Veterinary Research Institute, Izatnagar-243 122, Bareilly, UP, India |
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Abstract: | Opiates are known to inhibit electrically-evoked twitches of longitudinal muscle-myenteric plexus strips from guinea-pig ileum. When this preparation was incubated with morphine for 1 h tolerance developed to the inhibitory effect, since dose-response curves were shifted to the right. In the present study, the effects of alpha-2 adrenergic agents on the tolerance induced by morphine in this preparation was investigated. Addition of yohimbine 10 microM (but not 0.1 or 1 microM) to the incubating medium reduced the magnitude of opiate tolerance. This effect did not appear in the presence of the alpha-2 agonists clonidine or guanfacine (10 microM). Our results provide evidence of the longitudinal muscle-myenteric plexus as a useful model for the study of the relationship between morphine tolerance and alpha-2 adrenergic mechanisms. |
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