Detrusor smooth muscle contains muscarinic receptors of the M-2 (approximate to2/3) and M-3 (approximate to1/3) subtypes. M-3 receptors are mainly responsible for normal micturition contraction, whereas, the role Of M-2 receptors has not yet been clarified. In certain disease states, M-2 receptors may also contribute to bladder contraction. Different muscarinic receptor subtypes can contribute to processes of cellular activation or inhibition. For example, in salivary glands, both M-1 and M-3 receptor subtypes may control secretion. In the cardiovascular system, the M-2 receptor subtype can mediate parasympathetically-driven bradycardia and a decrease in cardiac output. In the brain, where the role of cortical M, receptors in cognition is well documented, M-1 receptor blockade would be expected to compromise central nervous system function. Muscarinic receptors that mediate contraction of human ciliary muscle are most probably M-3 and M-5. Drugs selective for the M-3 receptor might be expected to have clinical efficacy in detrusor overactivity with a reduction in adverse events related to the blockade of other receptor subtypes. However, the clinical effectiveness of a drug depends not only on its receptor affinity, but also on its pharmacokinetics and the importance of specific muscarinic receptors for a given organ function. (C) 2002 Elsevier Science B.V. All rights reserved.
- Farmakologi och toxikologi