Muscarinic cholinoceptors in the rabbit's myometrium: a study of the relationship between binding and response.

The relationship between 3H-quinuclinidyl benzilate ( 3HQNB) binding and muscarinic cholinoceptors in the myometrium of the oestrogen treated rabbit was studied. 3HQNB binding was specific, saturable and reversible. The ability of muscarinic agonists and antagonists and some of their stereoisomers to inhibit 3HQNB binding and to stimulate or inhibit contraction of the myometrium were almost identical suggesting that 3HQNB binds specifically to the muscarinic cholinoceptor in this tissue. There appeared to be no receptor reserve in this tissue and whilst structural and stereospecific requirements for binding were almost identical to those for the muscarinic cholinoceptor in the guinea pig ileum requirements for activation were not. Competition binding experiments with pirenzepine suggested that antagonist binding sites were heterogeneous whilst those with 4-diphenylacetoxy-N-methyl-piperidine MeBr did not. Results were discussed with regard to simple and complex models of muscarinic cholinoceptor interactions.