RELATION OF MOTOR AND INHIBITOR EFFECTS OF LOCAL HORMONES

Publisher Website
Google Scholar
Abstract
The role of acetylcholine in local regulation of tissue activity was studied in the intestines and auricles of the rabbit. In the auricles acetylcholine is synthesized and is responsible for maintaining rhythmic contraction. When synthesis of acetylcholine is optimal, the heart contracts efficiently; addition of extra acetylcholine at this point depresses the contractions by depressing the synthesis. If auricles continue to beat until they are exhausted, synthesis declines, but beat and synthesis can be restored by acetylcholine, which then acts as an autocatalyst. Thus acetylcholine has not only an inhibitory but also a stimulant action on the auricles, both being due to an action on acetylcholine synthesis. Auricular contractions can be started again by acetylcholine after arest by the antimalarial, proguanil. The mechanism of this action is explained. Both stimulant and inhibitory actions of acetylcholine can be demonstrated likewise in visceral smooth muscle. High concns. of acetylcholine inhibit smooth muscle. Similarly, in the blood vessels acetylcholine has both a normal inhibitory or dilator action and a stimulant action visible in the vessels of the rabbit ear, after long-continued perfusion with Locke''s soln. The relation of the motor and inhibitory actions of acetylcholine in smooth muscle is discussed. A hypothesis is put forward to explain the reversal of epinephririe action on the blood vessels by various agents. The relation of the action of norepinephrine to that of epinephrine in various tissues is considered in the light of the effects of denervation. The general theory is propounded that acetylcholine, histamine and epinephrine act as local hormones, and that several medicinal agents such as procaine, quinidine, demerol and benadryl exert their effects by competing with these local hormones.
Keywords