CHROMOGRANIN-A - SECRETION OF PROCESSED PRODUCTS FROM THE STIMULATED RETROGRADELY PERFUSED BOVINE ADRENAL-GLAND

Chromogranin A (CGA) is a member of a family of highly acidic proteins co-stored and co-secreted with adrenaline and noradrenaline in the adrenal medulla. A number of biologically active fragments of CGA (CGAFs) have been characterized including a group of small N-terminal fragments collectively named vasostatins due to their vascular inhibitory activity. In the present study, the release of CGAFs, including CGA N-terminal fragments, from the isolated, retrogradely perfused bovine adrenal gland, has been studied under basal conditions and during nerve stimulation and perfusion with acetylcholine. The CGAFs were characterized by SDS-PAGE followed by immunoblotting with antisera to specific sequences within the CGA molecule. Many different CGAFs were released during stimulation of the glands. Antisera to CGA1-40 and CGA44-76 detected a 7 kD protein whose release was increased during stimulation. This component co-migrated with synthetic CGA1-76, was not immunoreactive to antisera to CGA79-113 or CGA124-143, and was seen whether or not the serine protease inhibitor aprotinin was present in the perfusion medium. The release of an approximately 18 kD component, which stained with antisera to CGA1-40, CGA44-76 and CGA79-113, but not to chromostatin (CGA124-143), was also increased during stimulation. Components of 22 kD and larger were detected with antisera to chromostatin, but not with antisera to CGA1-40, CGA44-76 and CGA79-113. Two of these components of 22 to 24 kD were enhanced during nerve stimulation in the presence of aprotinin. The results indicate that processed chromogranin A fragments are secreted from the bovine adrenal medulla during stimulation of chromaffin cells. The major fragments secreted appear to be the N-terminal fragments of CGA, CGA1-76 and CGA1-113, which would arise as a result of processing of CGA at the first and second pairs of basic amino acids. A number of larger CGAFs, possibly containing the chromostatin sequence CGA124-143 at their N-terminal, and components similar in size to intact CGA and to proteoglycan forms of CGA, are also secreted from the perfused bovine adrenal gland during stimulation.