Differential subcellular localization of ACTH and ?-MSH in corticotropes of the rat anterior pituitary

Abstract

Specific antisera to alpha-melanotropin (alpha-MSH) and corticotropin (ACTH 1-39) were used to obtain immunocytochemical evidence for the differential localization of alpha-MSH and ACTH in the secretory granules of corticotropes of rat anterior pituitary. The specificity of the antisera was established by binding 131I-labeled alpha-MSH and ACTH 1-39 to their respective antisera. Double-labeling immunocytochemistry (for alpha-MSH, ferritin; for ACTH, colloidal gold) was performed. Some secretory granules were labeled with ferritin particles (alpha-MSH), whereas others contained gold particles (ACTH). Only a few granules showed both ACTH and alpha-MSH. In typical corticotropes (stellate in form with a small number of secretory granules aligned along the cell periphery) only some of the secretory granules that were labeled with anti-ACTH serum were also immunoreactive to anti-alpha-MSH. In atypical corticotropes (polygonal in shape and containing a large number of secretory granules) almost all of the immunoreactive ACTH secretory granules were also positive to anti-alpha-MSH serum. An intermediate type of corticotrope was observed containing a small number of secretory granules, almost all of which were labeled with anti-alpha-MSH. Thus, rat anterior pituitary corticotropes may be classified into three types according to the distribution and content of alpha-MSH. The light-microscopic immunocytochemistry provided similar results.

Adrenocorticotropic Hormone in Relation to Interrenal Function during Stress in Tilapia (Oreochromis mossambicus)

“…The presence of a-MSH did not result from contamination of the PD with NIL tis sue or of residual NIL a-MSH on the HPLC column, since the ratio between the three a-MSH forms was different between the two tissues. The processing of ACTH into desacetylated a-MSH in particular has also been demonstrated in the corticotropes of other vertebrates (Tanaka and Kurosomi, 1986;Dores et al, 1993). A function of this process is unclear, but it has been observed to be most prominent during fetal/ neonatal developmental stages (Dores et al, 1993) and to be under regulation by CRH (Iturriza and Ferese-Spinelli, 1991).…”

Intrapituitary Regulatory System of Proliferation of Mammotrophs in the Pituitary Gland

“…In rat pituitaries, mammotrophs in the central region of the anterior pituitary stimulate PRL secretion and cell proliferation in response to α-MSH (Porter and Frawley, 1992). During the postnatal ontogeny period, α-MSH is clearly localized in the mouse anterior pituitary (Marcinkiewicz et al, 1993), while corticotroph subpopulations in adult female rat pituitaries produce α-MSH as described above (Tanaka and Kurosumi, 1986). Therefore, it is possible that α-MSH produced in the anterior pituitary controls the functioning of mammotrophs in a paracrine manner.…”

“…α-MSH is mainly produced in the intermediate lobes, while a light and electron microscopic study revealed that it is also produced in the corticotrophs of adult female rat pituitaries (Tanaka and Kurosumi, 1986). α-MSH stimulated PRL secretion and the proliferation of mammotrophs through melanocortin-3 receptor (MC3-R) (Morooka et al, 1998;Matsumura et al, 2003).…”

Stress‐Related Changes in β‐Endorphin Processing: The Limitations of Slaughterhouse Material

“…This enzyme, plus increased carboxypeptidase activity (or a specific glucocorticoid-sensitive enzyme), may thus be crucial in the generation of NacaEP, the principal acetylated species produced in the abattoir/glucocorticoid-treated anterior pituitaries. Another possibility is the differential accumulation of the various POMC products in subpopulations of POMC-producing cells (19,20), which may be sensitive to different regulatory mechanisms (2 I), perhaps reflecting a heterogeneous distribution of releasable pools, as suggested by Ham and Smyth (9,14). The possibility also remains that these processing effects simply represent a change in intracellular steady state.…”