In vitro release of ACTH from dispersed rat pars intermedia cells. II. Effect of neurotransmitter substances.

Studies were carried out to test the responsiveness of dispersed pars intermedia (PI) cells to a number of neurotransmitter substances known to be present in the PI. These substances were tested over an extended dose range. The catecholamines, adrenaline, noradrenaline, and dopamine inactivated PI ACTH at high concentrations; at lower concentrations, they were without effect. Histamine and carbachol had no effect on ACTH release. 5-hydroxytryptamine stimulated ACTH release in a dose-related manner, from 10(-6) to 10(-3)M, while having no effect on ACTH release from the pars distalis (PD). We conclude that the release of ACTH from the PI may be controlled by direct serotonergic innervation.