A methodological basis for improving the reliability of measurements of opiate abstinence responses in the Guinea-Pig ileum made dependent in vitro

Abstract The purpose of this study was to find a neurogenic response of the isolated guinea-pig ileum that could serve as an internal standard to normalize abstinence responses, which are also neurogenic, during opiate dependence produced in vitro. The internal standard is required because of baseline variability in these responses of the ileum and a time-dependent decay in neuroeffector responsiveness with prolonged incubation. Systematic studies were made of the variability in the responses to neurogenic stimulation by 1) electrical field stimulation, 2) nicotinic stimulation, and 3) precipitation of opiate abstinence with opiate antagonists as well as studies of the time-dependent decay in responsiveness with prolonged incubation. The three neurogenic responses show covariation but the best correlation is found between the nicotinic and the abstinence responses. The nicotinic system presents a pharmacological sensitivity to specific acute opiate action and also shows an improving correlation with abstinence which develops with the progression of dependence. This correlation tends to a direct linear relation with a slope approaching 1.0. The nicotinic response of the ileum seems to be a valid internal control to normalize its abstinence responses after incubation with opiates for different intervals of time.