Ultrastructural Changes Accompanying the Stimulatory Effect of N6-Monobutyryl Adenosine 3’,5’-Monophosphate on the Release of Growth Hormone (GH), Prolactin (PRL) and Adrenocorticotropic Hormone (ACTH) in Rat Anterior Pituitary Glandin Vitro

In order to clarify the role of cyclic AMP on the hormonal release processes of the adenohypophysis, the effect of the cyclic nucleotide on both ultrastructure and hormone secretion of incubated rat adenohypophysis was studied at different times of incubation (5 min to 6 hr). Stimulation of the release of GH and PRL occurs in the first minutes following the addition of cyclic AMP. The stimulatory effect of cyclic AMP is specially marked during the first hour of incubation and it decreases gradually during the next five hours of incubation. In both somatotrophs (GrH-secreting cells) and mammotrophs (PRLsecreting cells), exocytosis is seen in most cells 5 min after the addition of cyclic AMP. One hr after addition of the cyclic nucleotide, most of these two cell types are almost completely degranulated. The remaining granules are located along the plasma membrane in the somatotrophs but remain more dispersed in the mammotrophs. At the longest time intervals, the Golgi apparatus containing immature granules is occupying a large portion of the cell surface. This hypertrophy is mainly due to a marked increase of the number of associated vesicles. The release of ACTH increased 30 min after the addition of cyclic AMP, the level of stimulation remaining on a plateau afterwards. At the ultrastructual level, the corticotrophic cells show a very active Golgi apparatus containing immature granules, but no convincing evidence of secretory granule depletion. In gonadotrophic and thyrotrophic cells, no convincing depletion of secretory granules or hypertrophy of the Golgi apparatus can be noticed. The ultrastructural changes induced by cyclic AMP in GH-, PRL- and ACTH-secreting cells appear similar to those already observed under the influence of purified hypothalamic releasing factors. (Endocrinology91: 1355, 1972)