Abstract
The binding characteristics of muscarinic receptors in rat salivary and lacrimal glands were studied by means of radioligand binding techniques. In competition experiments against [ 3H]N-methylscopolamine, classical muscarinic antagonists ipratropium bromide, N-methylscopolamine and N-methylatropine exhibited very similar K D values in all the glands and their binding behaviour was well described by a one binding site model ( nH ⋍ 1 ). The novel cardioselective antimuscarinic compound, AF-DX 116, displayed an equally low affinity in all the tissues examined. Pirenzepine and dicyclomine, two other selective muscarinic antagonists, showed a similar behaviour in all but the sublingual gland, where their binding profile indicated the presence of a heterogeneous receptor population (nH = 0.74 and 0.84, respectively). Histological studies of the sublingual-submandibular glandular complex demonstrated the presence of ganglionic structures mainly located in the hilum of the sublingual-submandibular glandular complex connected with the sublingual gland. Binding studies carried out with pirenzepine on the hilum and on a synaptosomal preparation from this region again revealed the presence of two populations of muscarinic receptors with K D values of 22–25 and 270–463 nM. These results are best explained by the presence of M 1 and M 2 receptors located on neuronal and glandular structures.
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