A previous study showed that thyroxine administration increased the decrement in muscarinic receptor agonist, acetylcholine-caused contraction in the thyroidectomized rat bladder.16 Also, the castrated rat bladder displayed decreased carbachol-induced contractile responses, and T treatment normalized the decrement.17 These findings suggest that hypothyroidism is likely to reduce muscarinic receptor-mediated contractility in smooth muscle, and the M2 muscarinic receptor agonist contractile responses are more associated with serum T levels than the regulation of T4 levels. Here, CHRM2 is linked to hypothyroidism.