VARIATION IN THE AFFINITY OF AMITRIPTYLINE FOR MUSCARINE RECEPTOR SUBTYPES

The affinity of amitriptyline for muscarine M(1) receptors was studied in the rat cerebral cortex and rabbit vas deferens utilizing binding studies as well as inhibition of carbachol-induced phosphoinositide hydrolysis in the cerebral cortex and blockade of the muscarinic prejunctional inhibition of sympathetic nerve stimulation in the rabbit vas deferens. The inhibition constants (K-I) or dissociation constants (K-B) Obtained were approximately 6- to 20-fold lower than those obtained at muscarine M(2) receptors in rat atria (binding and negative inotropic response) indicating that amitriptyline exhibits a degree of muscarine M(1) receptor selectivity.