[Co-release of neuropeptides and catecholamines by adrenal medulla]

Different neuropeptides are costored together with catecholamines in the adrenal medulla. The concurrent release of these neuropeptides [neuropeptide Y (NPY), met-enkephalin (ME)] and catecholamines (adrenaline and noradrenaline) from the adrenal gland was examined in chloralose-anesthetized dogs after intravenous administration of dihydralazine (1 mg/kg) and insulin (0.3 U/kg). These results were compared to those obtained after the stimulation of the right splanchnic nerve at 1, 5 and 10 Hz frequencies. Baroreflex involvement or hypoglycemia induced a significant preferential increase in CA and ME versus basal values: around 16 fold for dihydralazine and 28 fold after insulin administration. In opposite, increase in NPY was only two times baseline. Splanchnic nerve stimulation induced a frequency-dependent increase in catecholamines and neuropeptides. At the lower frequencies (1 to 5 Hz), splanchnic nerve stimulation elicited a parallel increase in catecholamines and ME (13 to 17 fold basal values). By contrast, NPY increases 2 fold in the same conditions. At the higher frequencies (5 to 10 Hz), we observed a parallel (4 fold) increase in NA, ME and NPY adrenal plasma levels. In conclusion, the present data indicate that both adrenal ME and catecholamines (mainly NA) always exhibit a parallel fashion of corelease which is not the case for NPY and that different populations of chromaffin vesicles could be preferentially mobilized according to different physiological and pharmacological patterns.