Expression of proadrenomedullin derived peptides in the mammalian pituitary: Co-localization of follicle stimulating hormone and proadrenomedullin N-20 terminal peptide-like peptide in the same secretory granules of the gonadotropes

Expression of proadrenomedullin-derived peptides in the rat, cow and human pituitary was studied by a variety of techniques. Immunocytochemical detect ion showed a widespread expression of adrenomedullin peptide in the adenohy pophysis and the neural lobe, with low expression in the intermediate pitui tary. Proadrenomedullin N-20 terminal peptide (PAMP)-immunoreactivity was a lso present in the anterior pituitary but showed a more marked heterogeneou s distribution, with cells going from very strong to negative immunostainin g. Lower levels of PAMP were found in the neural lobe. Interestingly, the d istribution of adrenomedullin and PAMP immunoreactivity in the anterior pit uitary did not completely overlap. In the present study, we concentrated ou r efforts to determine which cell type of the adenohypophysis expresses PAM P. Paraffin and semithin serial sections immunostained for PAMP and the cla ssical pituitary hormones revealed that a subpopulation of the gonadotropes expresses high levels of PAMP-immunoreactive material. Ultrastructural ana lysis clearly showed PAMP-immunoreactivity in the follicle stimulating horm one (FSH)-containing large secretory granules of the gonadotropes, suggesti ng simultaneous secretion of PAMP and FSH by this cell type. Three mouse ad enohypophysis-derived cell lines (AtT20, GH3, and alpha T3-1 derived from c orticotropes, lacto/somatotropes and gonadotropes, respectively) were also analysed and showed expression of both proadrenomedullin-derived peptides a nd their mRNA. Functional studies in these three cell lines showed that nei ther adrenomedullin nor PAMP was able to stimulate cAMP production in our e xperimental conditions. Taken together, our results support that proadrenom edullin derived peptides are expressed in the pituitary in cell-specific an d not overlapping patterns, that could be explained by differences in postr anslational processing. Our data showing costorage of PAMP and FSH in the s ame secretory granules open a way by which PAMP could be involved in the co ntrol of reproductive physiology in a coordinated manner with FSH.