CHARACTERIZATION OF EXTRACELLULAR PH DROP DUE TO THE ACTIVATION OF THE SECRETORY PROCESS BY ACETYLCHOLINE IN THE BOVINE ADRENAL-MEDULLA

A progressive and reversible decrease of external pH accompanied the c atecholamine release elicited by acetylcholine in decorticated bovine adrenal glands perfused with buffer-free Locke solution adjusted to an initial pH of 7.4. Both the secretory response as well as the extrace llular acid shift promoted by the cholinergic agonist were antagonized by hexamethonium plus atropine, Mg2+ and verapamil. Experiments perfo rmed to assess the effects of the reduction of external pH on acetylch oline-induced release of catecholamines revealed that increasing the e xtracellular concentration of H+ significantly and reversibly reduced this secretory response. These findings are consistent with the idea t hat adrenomedullary activation of secretion by acetylcholine could be associated with a transient acidification of the extracellular fluid, This release of protons, arising mainly from the chromaffin granules, may be involved in a local automodulatory mechanism of the regulated s ecretory process.