BIOACTIVE PEPTIDES IN ANTERIOR-PITUITARY-CELLS

The anterior pituitary (AP) has been shown to contain a wide variety o f bioactive peptides: brain-gut peptides, growth factors, hypothalamic releasing factors, posterior lobe peptides, opioids, and various othe r peptides. The localization of most of these peptides was first estab lished by immunocytochemical methods and some of the peptides were loc alized in identified cell types. Although intracellular localization o f a peptide may be the consequence of internalization from the plasma compartment, there is evidence for local synthesis of most of these pe ptides in the AP based on the identification of their messenger-RNA (m RNA). In several cases the release of the peptide from the AP cell has been shown and regulation of synthesis, storage and release have also been described. Because the amount of most of the AP peptides is very low (except for POMC peptides and galanin), endocrine functions are n ot expected. There is more evidence for paracrine, autocrine, or intra crine roles in growth, differentiation, and regeneration, or in the co ntrol of hormone release. To demonstrate such functions, in vitro AP e xperiments have been designed to avoid the interference of hypothalami c or peripheral hormones. The strategy is first to show a direct effec t of the peptide after adding it to the in vitro system and, secondly, to explore if the endogenous AP peptide has a similar action by using blockers of peptide receptors or antisera immunoneutralizing the pept ide.