Regulatory peptides—The distribution of two newly discovered peptides: PHI and NPY

PHI (peptide with histidine and isoleucine) and NPY (neuropeptide with tyrosine) are recently discovered regulatory peptides. There are close sequence similarities betwen PHI and both growth hormone releasing factor (GRF) and vasoactive intestinal polypeptide (VIP) and between NPY and pancreatic polypeptide. Using immunocytochemistry and radioimmunoassay we have revealed the broad distributions of PHI and NPY in neurons of the central nervous system and the majority of peripheral tissues. Tissues which are particularly well provided with these peptides include gut, pancreas, respiratory tract, skin and the genitourinary and cardiovascular systems. In most peripheral tissues, PHI-containing ganglion cells occur locally. NPY-containing fibres originate in part from cell bodies outside the tissues, in the sympathetic nervous system. Comparative studies indicate that PHI and VIP are co-stored in the same neurone and are identically distributed, thus suggesting the existence of a common precursor and subsequent gene duplication. The possible co-existence of catecholamines and NPY, suggested by the consistent finding of very similar distributions of the two substances, was investigated using antibodies to converting enzymes involved in catecholamine synthesis (tyrosine-hydroxylase and dopamine-β-hydroxylase). The two enzymes and NPY were found together in at least part of the same neuronal system.