Antagonism of acetylcholine by (+)- and (-)-hyoscyamine

Relationship between anti-acetylcholine and anti-Tremorine activity in anti-parkinsonian and related drugs

The anti-acetylcholine potency of a number of anti-Parkinsonism drugs and related phenothiazine compounds was determined using the isolated guinea-pig ileum. The antagonism was assessed by the difference between the pA(2) and pA(10) values and by log concentration-response curves for acetylcholine in presence and absence of the antagonists. All compounds except chlorpromazine showed some evidence of competitive antagonism to acetylcholine. The anti-tremor potency of the compounds was assessed from suppression of Tremorine-induced tremors in mice. There was a relation between anti-acetylcholine and anti-Tremorine potency among the anti-Parkinsonism drugs, but not among the phenothiazine compounds. Some implications of the findings are discussed in relation to the mode of action of anti-Parkinsonism drugs.

Some quantitative uses of drug antagonists. 1958

Various applications of p Ax measurements are discussed based on the hypothesis that drugs and drug antagonists compete for receptors according to the mass law. Examples are given illustrating the use of p Ax measurements to identify agonists which act on the same receptors and to compare the receptors of different tissues. Tests of competitive and noncompetitive antagonism are considered in relation to the antagonisms acetylcholine-atropine, histamine-atropine and acetylcholine-cinchonidine. A new measure, p Ah, is introduced to express the activity of unsurmountable antagonists.