NEUROPEPTIDES AND CORELEASE OF CATECHOLAM INES FROM THE ADRENAL-GLAND

Different neuropeptides are costored together with catecholamines in t he adrenal medulla. The concurrent release of these neuropeptides [neu ropeptide Y (NPY), metenkephaline (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 o btained after the stimulation of the right splanchnic nerve at 1, 5 an d 10 Hz frequencies. Baroreflex involvement or hypoglycemia induced a significant preferential increase in CA end ME versus basal values: ar ound 16 fold for dihydralazine and 28 fold after insulin administratio n. In opposite, increase in NPY was only two times baseline. Splanchni c nerve stimulation induced a frequency-dependent increase in catechol amines and neuropeptides. At the lower frequencies (1 to 5 Hz), splanc hnic 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 ob served a parallel (4 fold) increase in NA, ME and NPY adrenal plasma l evels. In conclusion, the present data indicate that both adrenal ME a nd catecholamines (mainly NA) always exhibit a parallel fashion of cor elease which is not the case for NPY and that different populations of chromaffin vesicles could be preferentially mobilized according to di fferent physiological and pharmacological patterns.