Aging: effects on chronotropic actions of muscarinic agonists in isolated rat atria.

Negative chronotropic effects of acetylcholine and carbachol were compared in right atria isolated from adult and aged Fischer 344 rats. Preparations from aged rats were more sensitive to the action of acetylcholine; however, there was no difference in responsiveness to carbachol or to acetylcholine after pretreatment with diisopropylfluorophosphate, an irreversible cholinesterase inhibitor. These data suggest that the enhanced sensitivity to the direct chronotropic action of acetylcholine is the result of aging-related reductions in acetylcholinesterase activity.