HYDROLYSIS OF ACETYLCHOLINE BY TISSUES

¹ Department of Pharmacology, University of Edinburgh

1. The frog's auricle wetted with Ac.Ch. solution recovers activity at a rate dependent on the initial concentration of drug. The form of recovery and also the relations between initial concentration of Ac.Ch. and the rate of recovery both indicate that the esterase activity of the auricle is equal to that produced by a concentration of enzyme centres equal to 2 x 10^-5 molar. There is a considerable individual variation in the esterase activity of auricles.

2. The relation between dosage of Ac.Ch. and the duratioln of fall of blood-pressure in the cat can be interpreted as regards the higher doses as an expression of esterase activity, but most of the Ac.Ch. introduced into the blood-stream is rapidly removed, probably by reversible adsorption by the tissues.

3. The recovery of the frog's auricle from Ac.Ch. and the duration of its action on the cat's blood-pressure are both prolonged by eserine and the consequent relations between concentration (or dosage) and duration can be interpreted as due to inhibition of all or at least the greater portion of the esterase.

4. The time for half hydrolysis of 1 in 10 million Ac.Ch. by the frog's auricle is about 20 secs., and the time for half hydrolysis of 1·0 µg./ kg. in the normal cat is between 5 and 10 secs.

The authors desire to express their thanks to the Moray Fund of the University of Edinburgh for a grant which defrayed the expenses of this research. One of the authors (J. R.) is in receipt of a grant from Messrs. Imperial Chemical Industries. We also desire to thank Messrs. E. Merck for kindly supplying carbaminoyl methyl choline.