High concentrations of neuropeptide Y have been found in many norephinephrine containing chromaffin cells in adrenal glands of various species. Adrenal gland seems to provide an interesting model system in which to investigate the functional role of NPY because evidence is accumulating that NPY may have modulatory effect on catecholamine. Previously, we have found that NPY can be released from bovine adrenal by acetylcholine. In the present study, the cholinergic receptor mediated secretion was further characterized by using retrogradedly perfused bovine adrenal glands. Infusion of acetylcholine produced a dose dependent increase in NPY secretion. Hexamethonium antagonized this NPY release whereas atropine did not. The role of the nicotinic cholinergic receptor in this process was further established by examining the effect of 1,1-dimethyl-4- phenlypiperazinium (DMPP). Infusion of DMPP also stimulated the NPY secretion. Biochemical analysis by HPLC revealed that four NPY immunoreactive peptides were secreted and the major immunoreactivity was identified to be authentic NPY. This release pattern of NPY is similar to that of catecholamines, thus it may be suggested that NPY is co-released with catecholamines by exocytosis via stimulation of nicotinic receptor. PReviously, we have found that NPY levels in rat adrenal glands increase markedly with age during maturation and furthermore, an additional NPY-like peptide is detected in adrenal glands of older rats but not in that of younger rats. The nature of this NPY-like peptide is presently unclear; however, further characterization of this NPY-like peptide indicates that it is not an oxidized form of NPY, PYY or a degraded fragment of NPY. Furthermore, this NPY-like peptide is present in splanchnic nerves and also in chromaffin cells and can be secreted upon stimulation of cholinergic receptor. Highly purified NPY-like material has been prepared from bovine adrenal glands and we are planning to examine the biological activity of this new peptide. It is known that NPY exerts direct vasopressor effect and potentiates catecholamine induced vasoconstriction; furthermore, NPY can be co-released with catecholamines from adrenal glands thus NPY may contribute to the cardiovascular effects seen upon adrenal activation.
