Effects of some isomers and analogues of nicotine on junctional transmission.

A number of isomers and homologues of nicotine, (2-, 3- and 4-pyridylmethyl)- and [2-(2-, 3- and 4-pyridyl)ethyl]- dialkylamines and trialkylammonium salts, have been prepared. They have been tested for their ability to act like acetylcholine in causing contracture of the chick biventer-cervicis and, some of them, for their ability to stimulate the superior cervical ganglion of the cat, causing contracture of the nictitating membrane. All the compounds have been tested for their ability to block transmission on the superior cervical ganglion of the cat and on the rat diaphragm preparation, and most of them for ability to inhibit the enzymatic hydrolysis of acetylcholine, using an acetone-powder of dog caudate nucleus as a source of acetylcholinesterase. The dissociation constants of the compounds have been measured by electrometric titration. The dissociation constants were used to compute the amount of monovalent ion present in the conditions of the biological tests, and the activities of the compounds have, accordingly, been compared on an ionic, as well as on a molecular, basis. The two sets of figures do not differ greatly. Trimethyl[2-(3-pyridyl)ethyl]ammonium (23) was the most potent compound on the chick and cat preparations. On an ionic basis (that is, compared with the monovalent nicotinium ion) this was 2.6 times as active as nicotine on the chick biventer and 11 times as active on the cat superior cervical ganglion. On the rat diaphragm it was 7.1 times as active as nicotine and less active than 1-methyl-1-(3-pyridylmethyl)-pyrrolidinium (26) (9.5 times the nicotinium ion) and trimethyl(4-pyridylmethyl)-ammonium (21) (11 times). The relationships between structure and dissociation constant, anticholinesterase activity, and activity in the pharmacological tests have been discussed.