Inhibitory regulation by co-released peptides of catecholamine secretion by the canine adrenal medulla

1. We have stimulated the peripheral end of the cut left splanchnic nerve in anaesthetized dogs while collecting the venous effluent of the left adrenal gland for catecholamine estimation. 2. With low frequency stimulation the resting output of catecholamines was inhibited but at high frequencies it was augmented. 3. The inhibition of catecholamine output by low frequency stimulation was reversed by opiate antagonists (naloxone and nalmefene) but enhanced by angiotensin converting enzyme inhibitors (captopril and enalapril).