CHANGES IN TRANSPORT CHOLINESTERASE LEVELS AND RESPONSES TO INTRAVENOUSLY ADMINISTERED ACETYLCHOLINE AND BENZOYLCHOLINE

¹ Department of Pharmacology, Georgetown University Medical School, Washington, D. C.

The hemodynamic responses to acetylcholine, methacholine and benzoylcholine, activities of acetyl- and pseudo-cholinesterase of blood and other tissues, and certain other variables have been investigated in dogs following infusion of several hours at the rate of 0.5 ml./kgm./minute with various physiological solutions.

Blood enzyme activity was lowered by less than 30 per cent and the responses to acetylcholine and benzoylcholine, but not to methacholine, were potentiated by this procedure.

Responses to these agents and activities of cholinesterases were also investigated following replacement of the blood of the recipients by the cholinesterase-free blood of DFP-treated donors, and also following replacement of the cholinesterase-free blood of DFP-treated recipients by the cholinesterase-rich donor blood. In the latter case, the recipients showed a normal blood cholinesterase activity in the absence of neuro-effector cholinesterases.

Lowering of the concentration of cholinesterases of the blood ("transport" enzyme) in the absence of change of the neuro-effector cholinesterases ("specific" enzyme) led to potentiation of responses to ACh and BCh. DFP further potentiated these responses.

Transfusion of cholinesterase-rich blood caused return of the potentiated BCh and ACh responses of the DFP-treated recipients to control values.

These data demonstrate the importance of "transport" cholinesterases in limiting the responses to hydrolyzable cholinergic agents.