Presence and Role of PACAP in Endocrine Glands of Mammals

PACAP is expressed and secreted by pituitary gonadotropes and folliculostellate cells, adrenal chromaffin cells, α- and β-cells of the Langerhans-islets, and some enteroendocrine cells. Low levels of PACAP produced by the abovementioned cells imply autocrine and paracrine actions. PACAP is also released into the portal circulation from some hypophysiotropic neurons and regulates pituitary functions. Because PACAP level is very low in the systemic circulation, other endocrine organs may not be under the influence of hypothalamic PACAP; however, they are innervated by PACAP immunoreactive sensory and the parasympathetic fibers. This means that PACAP is a neuromodulator in both the sensory and autonomic nervous systems of endocrine organs. The effect of PACAP is mediated through its specific receptors. The proliferating and differentiating effects of PACAP on endocrine tissues have also been demonstrated.