AbstractWe have compared the enkephalin‐like material derived from proenkephalin released from perfused cat adrenal glands stimulated with pilocarpine (5 X 10‐4M) and nicotine (5 X 10–6M). In addition, two doses of acetylcholine (10‐5 and 10‐4M) and 50 mM K+ were tested. Free Met‐enkephalin immunoreactivity and total Met‐enkephalin immunoreactivity, as determined by enzymatic digestion of large enkephalin‐containing fragments, were coreleased with catecholamines. Free Met‐enkephalin immunoreactivity represented 13% of total immunoreactivity for nicotinic stimulation, 46% for pilocarpine, 33% for 10‐5M acetylcholine, 22% for 10‐4M acetylcholine, and 16% for 50 mM K+. Analysis of the perfusate by gel filtration showed that 80% of the total Met‐enkephalin immunoreactivity whose release was induced by pilocarpine was eluted in fractions corresponding to fragments of low molecular weight, whereas these fractions accounted only for 10% of the total Met‐enkephalin immunoreactivity whose release was induced by nicotine. HPLC analysis of low‐molecular‐weight peptide fractions revealed that Met‐enkephalin, Met‐enkephalin‐Arg‐Gly‐Leu, and Met‐enkephalin‐Arg‐Phe represented 69% of total Met‐enkephalin immunoreactivity whose release was induced by pilocarpine. These results indicate that selective activation of muscarinic receptors is followed by release of low‐molecular‐weight material, whereas nicotine application also yielded high‐molecular‐weight peptides. Furthermore, increasing the acetylcholine concentration from 10‐5 to 10‐4M and using 50 mM K+ increased proportionally the high‐molecular‐weight peptide secretion. Results are discussed in relation to the existence of a heterogeneous population of granules, either in the same cell or in different cells, containing proenkephalin‐derived peptides. It appears that, under physiological conditions, different enkephalin‐containing peptides might be secreted from the cat adrenal gland. The response might also be modified when nonphysiologic stimuli are applied.