Ultrastructural Evidence for Endogenous Growth Hormone-Releasing Factor-Like Immunoreactivity in the Monkey Pituitary Gland

Abstract

Growth hormone-releasing factor-like immunoreactivity was visualized in monkey pituitary gland by immunocytochemistry on ultrathin sections obtained by cryoultramicrotomy. Antibodies were raised against synthetic human pancreas growth hormone-releasing factor (1–40). Growth hormone-releasing factor-like immunoreactivity was observed in somatotropes (identified by immunocytochemistry) only. The other pituitary cell types were not immunoreactive. In somatotropes, immunoreactivity was observed at the plasma membrane but only very scarcely, in the cytoplasm (cytoplasmic matrix and secretory granules) and in the nucleus. These results (1) provide immunocytological evidence for the presence of growth hormone-releasing factor or of an immunoreactive fragment of its molecule in the pituitary; (2) indicate the presence of this peptide in one particular pituitary cell type; and (3) provide cytological evidence for direct participation of growth hormone-releasing factor in the regulation of the somatotropic function.

Restricted Presence of the Growth Hormone-Releasing Hormone Receptor to Somatotropes in Rat and Human Pituitaries

“…This is in agreement with the literature indicating that male rat and human pituitaries contain 37–48% and 50% of somatotropes [34, 35], respectively. This is also in agreement with the exclusive specificity of action of GHRH in this cell population [36, 37, 38]and previous localization of 125 I-GHRH in rat [20]and immunoreactive GHRH in rat and monkey pituitaries [39, 40]. …”

“…The modest level of labeling at the plasma membrane is consistent with the limited surface area of this cell structure in 80-nm sections and with the low abundance of GHRH-R (17 fmol/10 6 ) in anterior pituitary cells [15]. GHRH-R labeling appeared to be associated with the membrane of GH-secretory granules, considering that a maximal resolution of ≈25 nm is obtained with this technique [39, 40]. This localization may suggest that the GHRH-R isoforms detected are not mainly processed through the endosomal pathway.…”

Heterogeneous Immunocytochemical Reactivities of oCRF-41-Like Material in the Human Hypothalamus, Pituitary and Gastrointestinal Tract

“…We were unable to identify oCRF-41 -like immunoreactivity in cells of rat pitui taries. Morel et al [7] found ultrastructural evidence of the presence of oCRF-41-like immunoreactive material in corti cotrophic cells of rat pituitaries with 4 oCRF-41 antisera, providing additional cytological evidence for participation of an oCRF-41 in the regulation of corticotrophic function. The did not mention, however, presence of oCRF-41-like immunoreactive material in rat growth hormone cells.…”

Immunohistochemical Localization and Radioimmunoassay of Corticotropin-Releasing Factor in the Forebrain and Hypophysis of the Frog <i>Rana ridibund</i><i>a</i>

“…In fact, we have already shown that other 'hypothalamic' peptides such as TRH, somatostatin and VIP are extremely abundant in the frog neurointermediate lobe [62], The absence of radioimmunoassayable CRF in the distal lobe, which is corroborated by our immunohisto chemical results, can be regarded as a proof for the speci ficity of both immunological methods. However, it should be mentioned that, using a very sensitive ultrastructural immunocytochemical technique, Morel et al [39] have been able to detect CRF-like material in the anterior lobe corticotrophs of the rat.…”

“…Production and characterization of the primary antisera have been described previously [10,II,39,47,59]. Staining was per formed by the peroxidase-antiperoxidase (PAP) technique [57] us ing one of the primary antisera which are listed in table 1.…”