[Action of physostigmine on the acetylcholine level of the bovine iris]

The work discusses the measurement of acetylcholine (ACh) in the bovine iris in 150 mg of tissue on guinea-pig ileum. Prior to the extraction of ACh, a 1% solution of physostigmine salicylate (eserine) was instilled into the conjunctival sac ten times at a dose of three drops at intervals of three minutes (to a total of 15,000 micron g). The fellow eye of the same animal was left untreated and served as a control. One hour after the least instillation the animal was killed. The nine eserinised irides showed an average of 0.65 micron g ACh, and the nine controls an average of 0.47 micron g ACh (for 150 mg of tissue). The difference was statistically significant. In the discussion the authors admit that the amplitude of contraction of the guinea-pig ileum can be very little influenced by traces of eserine, possibly by binding effect. The form of eserine applied no longer influences the amplitude of the guinea-pig ileum contractions after an hour of in vivo action, and this is the same in considerably smaller doses where it is possible to prove its inactivation. Augmentation of the activity in the eserinised iris is adequate for the levels of acetylcholine. The more intensive action of eserine on the iris compared to that of pilocarpine is related to its greater binding power with the iris tissues.