[Effect of pituitary adenyl cyclase activating polypeptide on the cells of anterior pituitary cells]

Pituitary adenylate cyclase activating polypeptide was first isolated from sheep hypothalamus by its potent activity in stimulating cyclic adenosine monophosphate production in anterior pituitary cells. The present review deals with the actions of this polypeptide on anterior pituitary cell types and with the putative role of the polypeptide as a hypophysiotropic factor regulating anterior pituitary cell activity. The evidence to date is strongly suggestive that pituitary adenylate cyclase activating polypeptide may act not as a "classic" hypophysiotropic factor stimulating or modifying anterior pituitary hormone release in vivo, since it does not appear in vitro to be a particularly potent stimulator of hormone release. The polypeptide rather may modulate the responses to factors such as gonadotrop hormone releasing hormone or have more general actions by regulating hormone synthesis or cell differentiation. Pituitary adenylate cyclase activating polypeptide also has indirect actions on anterior pituitary cell activity by stimulating the release of the paracrine factor interleukin-6. Its receptors appear to be present on most of the anterior pituitary cell types and unlike many other hypophysiotropic factors, pituitary adenylate cyclase activating polypeptide interacts with most, if not all, of the anterior pituitary cell types. Its exact effects and mechanisms of action in the anterior pituitary gland are still poorly understood.