Immunohistochemical analysis of the localization of neuropeptides in the adrenal gland.

Recent advances in immunohistochemical studies have revolutionalized our understanding of the adrenal gland with the discovery that many neuropeptides exist in the chromaffin cells and intraadrenal neuronal components. The coexistence of peptides and catecholamines is a constant feature of the chromaffin cells. The coexistene of multiple peptides is also seen in some chromaffin cells. This indicates that there are several subpopulations among the chromaffin cells in terms of bioactive substances contained. Diverging from the traditional view that intraadrenal nerves are predominantly preganglionic cholinergic ones innervating the chromaffin cells, the nerves are revealed to consist of heterogeneous populations containing various different neuropeptides. These are presumed to be of several different origins. The nerves innervate not only the chromaffin cells but partially the cortical cells, too, and are further associated with intraadrenal blood vessels. Several possible courses of action for the neuropeptides in the adrenal gland have been proposed based on immunohistochemical findings. The adrenal gland should be regarded as an endocrine organ, secreting not only catecholamines but also various neuropeptides; it likely plays more important and varied roles than previously believed for the maintainance of the internal environment of the body.