Abstract

Dose-response curves have been run on isolated chains of rabbit aorta with acetylcholine alone and with acetylcholine in the presence of epinephrine, norepinephrine, or of serotonin. Under the latter conditions, when tone was present, the primary effect (observed with the lowest doses) of acetylcholine was that of relaxation. Higher concentrations then caused a variable contraction, the amplitude of which compared favorably with that seen with acetylcholine alone when no tone was present. Still higher concentrations of acetylcholine caused a relaxation once again. Both these dilator and constrictor effects of acetylcholine appeared to be relatively independent of the presence or concentration of serotonin.

Under these conditions, acetylcholine appears to act in a manner similar to that seen in perfused vascular systems and in vivo. These findings appear to resolve some problems concerning the effects of acetylcholine in vascular smooth muscle, and lead to further speculation as to the mechanism of its action.