The relationship of pharmacological response and age: the action of acetylcholine and atropine on the gastrointestinal tract of the adult and unweaned rat
Goldman, William Joseph
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Since acetylcholine has been established as the mediator of peristaltic activity in the adult, studies were carried out to determine whether there is a quantitative or qualitative difference in the response to acetylcholine of the neonatal rat. Sprague-Dawley rats were used throughout the experiments. Infants were randomly selected from litters born in our own animal farm. The infants were allowed to remain with their mothers until immediately before the experiment. For the adult experiments, male rats weighing between 130-230 gm were used. On the day before the experiment, food was removed from the latter animals but free access to a 5% glucose solution was permitted. To compare the gastrointestinal motility of the neonatal and adult animal, the in vitro experimental procedure of Magnus, slightly modified, was used. The tissue bath contained 0 Krebs-Henseleit buffer, pH 7.4, preheated to 37 C and aerated with a 95% o2 and 5% co2 mixture. The intestinal segment was attached to a Grass FT 03 transducer which was connected to a Grass Polygraph. The parameters of the isometric contractile responses to acetylcholine of the isolated tissue which were of principal concern included: the maximum tension developed (equivalent to peristalsis); the rate of change of developed tension; the optimum applied tension, and the potency of the applied acetylcholine. Additional information concerning the interaction of the applied acetylcholine with its receptor required the inclusion of specific antagonists and synergists into the experimental protocol. [TRUNCATED]
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