Cyproheptadine displays high affinity for muscarinic receptors but does not discriminate between receptor subtypes

The affinity of cyproheptadine for different muscarinic receptor subtypes was investigated in vitro by functional experiments in field-stimulated vas deferens of the rabbit (ganglionic M1- and cardiac M2-receptors) and in guinea-pig ileum (smooth muscle M3-receptors). Cyproheptadine displayed high but similar affinity for all muscarinic receptor subtypes studied (pA2 = 7.99-8.02). In contrast, (+)-telenzepine (M1 over M2 and M3), and for mefurtramine (M2 over M3 and M1) were found to be selective.