ABSTRACT
Medicinal chemists have produced a large number of alpha, beta, and muscarinic receptor blockers. With the development of H-3-labeled substrates, mostly antagonist, the concentration of a-adrenergic receptors, beta adrenoceptors, and muscarinic receptors have been quantified using in vitro techniques in various animal species. The concentration of the muscarinic receptor in the base of the left ventricle in both pmol/g protein and pmol/g tissue is 109.2 and 16.6 in the rat, 39.8 and 6.0 in the rabbit, 151.0 and 15.3 in the guinea pig, and 100.7 and 10.4 in the dog, respectively. In general, the affinities of the beta adrenoceptors are lower than those for the alpha adrenoceptors or the muscarinic cholinergic receptors. The muscarinic cholinergic receptor system is attractive because of the high affinity of quinuclidinyl benzilate and the relatively high receptor concentration reported in the literature.
