Dynamics of subcellular organelles, growth hormone, Rab3B, SNAP‐25, and syntaxin in rat pituitary cells caused by growth hormone releasing hormone and somatostatin

Abstract

Rab3B is involved in the exocytosis of synaptic vesicles and secretory granules in the central nervous system and the anterior pituitary cells. The aim of this study was to elucidate both the role of rab3B in GH secretion and the mutual relationship of rab3B and SNARE proteins. Adult male rats were injected intravenously with 10 microg of growth hormone releasing hormone (GHRH) or 10 microg of somatostatin (SRIF). Untreated rats were used as controls, and their pituitary glands were sectioned for histochemical examination. Rab3B is localized on the limiting membrane of the secretory granules and the cytosol. Confocal laser scanning microscopic observation of immunohistochemical double staining of rab3B and GH revealed that immunoreactivity of rab3B increased in GHRH-treated rats and decreased in SRIF-treated rats. Confocal laser scanning microscopic observation of immunohistochemical double staining of SNAP-25, syntaxin, and rab3B revealed the co-localization of rab3B and these SNARE proteins in GHRH-treated rats, and their dissociation in SRIF-treated rats. These results suggest that rab3B plays a principal role in GH secretion in the anterior pituitary cells and that SNAP-25 and syntaxin act as co-workers with rab3B in the functional regulation of GH secretion.

Somatostatin system: molecular mechanisms regulating anterior pituitary hormones

“…Although it remains to be determined whether SRIF regulates pituitary Ca 2C levels independently of K C channels, GH release correlates with both frequency and amplitude of calcium oscillations, while calcium channel blockers and SRIF acutely suppress Ca 2C extrusion (Holl et al 1988). SRIF treatment resulted in Ca 2C -dependent redistribution of cytoplasmic microfilaments, without affecting intracellular somatotroph GH content (Shimada et al 1990), in addition to reduced association of exocytosis-associated RAB3B and SNARE proteins (Matsuno et al 2003 Adenylate cyclase/cAMP/PKA signalling SRIF inhibits pituitary adenylate cyclase/cAMP/PKA signaling, thereby inhibiting pituitary hormone synthesis and cell growth. SRIF inhibits cAMP production and ACTH secretion induced by CRH, forskolin, isoproterenol, vasoactive intestinal polypeptide (VIP), and cholera toxin in AtT-20 cells (Heisler et al 1982).…”

Molecular and Histological Studies of Pituitary Tumorigenesis Using Experimental Animal Models

“…For GHomas, GHRH has been emphasized by the hypersensitive immunohistochemical method [32] and this proposed molecular mechanism has been substantiated by GHRH transgenic (Tg) animals [41].…”

Functional and Morphological Analyses of Rab Proteins and the Soluble N-ethylmaleimide-sensitive Factor Attachment Protein Receptor (SNARE) System in the Secretion of Pituitary Hormones

“…1a-c) [24]. In rat pituitary cells treated with GHRH, one of the major stimulatory factors of GH production and secretion, increased rab3B immunoreactivity and decreased GH immunoreactivity are apparent.…”

“…Another important issue is the process of pituitary hormone secretion. We have investigated modulations of the intracellular dynamics of growth hormone (GH), rab3B, soluble N-ethylmaleimide- [24]. These proteins were found to display a close relationship in GH secretion [24].…”

“…We have investigated modulations of the intracellular dynamics of growth hormone (GH), rab3B, soluble N-ethylmaleimide- [24]. These proteins were found to display a close relationship in GH secretion [24]. This review article focused on functional and morphological analyses of rab proteins and the SNARE system in pituitary cells, including our studies on modulations of GH, rab3B, SNAP-25, and syntaxin in rat pituitary cells.…”