Antagonist discrimination between ganglionic and ileal muscarinic receptors

The effects of four antagonists on the depolarization of isolated superior cervical ganglia and the contraction of isolated ileal segments of the rat were compared. pA2 values estimated from Schild plots indicated significantly higher affinities of stercuronium (x100) and pirenzepine (x23) and a significantly lower affinity of 4-diphenylacetoxy-N-methylpiperidine methiodide (x0.39) for the ganglion than for the ileum. The affinities of N-methylscopolamine for the two tissues were not significantly different. It is concluded that the two types of muscarinic receptor are not identical.