Nanobiology and physiology of growth hormone secretion

Abstract

Growth hormone (GH) secretion is controlled by hypothalamic releasing hormones from the median eminence together with hormones and neuropeptides produced by peripheral organs. Secretion of GH involves movement of secretory vesicles along microtubules, transient 'docking' with the porosome in the cell membrane and subsequent release of GH. Release of GH is stimulated by GH releasing hormone (GHRH) and inhibited by somatostatin (SRIF). Ghrelin may be functioning to stimulate GH release from somatotropes acting via the GH secretagogue (GHS) receptor (GHSR). However, recent physiological studies militate against this. In addition, ghrelin does influence GH release acting within the hypothalamus. Release of GH from the somatotropes involves the GH-containing secretory granules moving close to the cell surface followed by transitory fusion of the secretory granules with the porosomes located in multiple secretory pits in the cell membrane. Other peptides/proteins can influence GH secretion, particularly in species of non-mammalian vertebrates.

Thyrotropin-Releasing Hormone (TRH) and Somatostatin (SST), but not Growth Hormone-Releasing Hormone (GHRH) nor Ghrelin (GHRL), Regulate Expression and Release of Immune Growth Hormone (GH) from Chicken Bursal B-Lymphocyte Cultures

“…As expected, the expression of GHRH, TRH, ghrelin, and SST mRNAs were found in the chicken hypothalamus used as control, confirming previous results regarding their hypothalamic production in several species, including avian models [36,37]. Additionally, the expression of GHRH-R, TRH-R, GHS-R1a, SST-Rs, and GH-R mRNAs were observed in the chicken pituitary control, in concordance with previous reports [38][39][40][41][42]; and GH-R mRNA was found in the liver. Here, we show that several components of the somatotropic axis, such as GH, TRH, ghrelin, and SST mRNAs, as well as GH-R, TRH-R, GHS-R1a, and SST-Rs (subtypes 1-5) mRNAs, are definitively expressed in chicken BBLs; however, neither GHRH nor GHRH-R mRNAs expression were detectable in these cells in our qPCR system.…”

“…The complex and fine-tuned Ca 2+ dynamics occur in variable timeframes (from milliseconds to minutes), in which effector or/and inhibitory molecules are activated, blocked, and biotransformed to control a wide variety of physiological functions. In the pituitary, Ca 2+ has a pivotal role in hormonal synthesis and secretion, in which hypothalamic hormones, such as GHRH, GnRH, TRH, CRH, and SST, are involved in an intricate system that includes transport and well-orchestrated changes between different cellular compartments [38]. Our study shows, for the first time, that TRH and SST exert actions upon intracellular Ca 2+ levels in BBLs.…”

Structure and Physiological Actions of Ghrelin

“…Besides, ghrelin acts in synergy with GH-releasing hormone (GHRH) on GH secretion [135, 142]. However, clinical studies have led to contradictory data concerning the relationship between GH and ghrelin circulating levels [143–148]. Most of these studies measured total ghrelin levels rather than acyl ghrelin levels and did not necessarily design protocols taken into account the pulsatility of both ghrelin and GH secretion.…”

Acylated ghrelin is not required for the surge in pituitary growth hormone observed in pregnant mice

“…Growth hormone (GH) release from the anterior pituitary gland classically involves stimulation by growth-hormone-releasing hormone (GHRH) and inhibition by somatostatin from the hypothalamus [1].…”