BAM-18P is the 18-residue member of the bovine adrenal medulla peptide series, sitting between BAM-12P and BAM-22P in length. Like the others it begins with the Met-enkephalin sequence and carries a C-terminal extension, and its pharmacology has been characterised in its own right rather than only inferred from the longer and shorter members. The series exists because proenkephalin A is processed to several peptides of differing length rather than solely to free enkephalins, and the extensions are not inert packaging. Within the BAM peptides, the C-terminal region confers activity at sensory-neuron-specific Mas-related receptors, while the shared N-terminus retains opioid activity, so each member represents a different balance between the two. Changes in opioid receptor selectivity across such peptides have been examined directly, and the practical consequence is that BAM-18P need not behave like a simple intermediate between its neighbours. This peptide is most useful where length dependence is the question: profiled alongside BAM-12P (LT1041) and BAM-22P (LT1042), it gives a third point on the extension-length series rather than the two endpoints alone, which is often what distinguishes a graded effect from a threshold one. Include an opioid antagonist control, since both receptor systems may contribute to any response observed. | 