Perifused adenohypophyseal cells: release of ACTH and kinetics of the response to secretagogues.

The release of ACTH-like immunoactivity (ACTH-LI) from perifused dispersed adenohypophyseal cells was examined under basal conditions and in response to various secretagogues. Frequent sampling of effluent perfusion medium and a variable stimulation format allowed us to discern differences in the effects of the secretagogues. The dye, dextran blue, was used to define the kinetics of flow intrinsic to the perifusion system, allowing a detailed analysis of the responses to secretagogues. Each agent had a time course of action which could be related to its supposed site and mode of action in these cells. A crude hypothalamic extract, a partially purified corticotrophin releasing factor preparation, 8-bromoadenosine 3',5'-cyclic monophosphate (8Br-cAMP), and 3-isobutyl-1-methylxanthine all caused dose-related, repeatable increases of the release of ACTH-LI. A 10-fold elevation in the concentration of K+ in the perifusion medium (10K) caused a transient increase in the release of ACTH-LI which was reduced when repeated. These results suggest that 10K stimulates the release of ACTH-LI only from a "readily-releasable pool." The other agents appear to affect the release process more profoundly, for example, by stimulating intracellular transport of the ACTH-LI.