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Activation of muscarinic receptors M2 and M4 inhibits adenylate cyclase which reduces cAMP levels. It would be expected that antimuscarinics such as ipratropium would increase cAMP levels. However, the pharmacological action of ipratropium is said to be mediated through increased cGMP levels [1]. Why is this the case?

[1] https://www.ncbi.nlm.nih.gov/pubmed/138578

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    $\begingroup$ M2 and M4 receptors are Gi-coupled receptors. M3 which is relevant for the effects of ipratropium is Gq coupled. Similar receptors have different effectors and therefore different effects on cAMP/cGMP. $\endgroup$ – Ashafix Mar 17 at 18:41

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