Anticholinesterase, any of several drugs that prevent destruction of the
neurotransmitter acetylcholine by the enzyme acetylcholinesterase within the
nervous system. Acetylcholine acts to transmit nerve impulses within the parasympathetic nervous system—i.e., that part of the
autonomic nervous system that tends to induce secretion, to contract smooth muscles, and to dilate blood vessels. In preventing the destruction of acetylcholine, anticholinesterase permits high levels of this neurotransmitter to build up at the sites of its action, thus
stimulating the parasympathetic nervous system and in turn slowing the heart action, lowering blood pressure, increasing secretion, and inducing contraction of the smooth muscles.