scholarly journals Growth hormone (GH)-releasing hormone and GH secretagogues in normal aging: Fountain of Youth or Pool of Tantalus?

2008 ◽  
Vol Volume 3 ◽  
pp. 121-129 ◽  
Author(s):  
Everly Macario
Keyword(s):  
Growth Hormone ◽  
Normal Aging ◽  
Releasing Hormone ◽  
Gh Secretagogues ◽  
Fountain Of Youth

scholarly journals From growth hormone-releasing peptides to ghrelin: discovery of new modulators of GH secretion

2006 ◽  
Vol 50 (1) ◽  
pp. 17-24 ◽  
Author(s):  
Ana Maria J. Lengyel
Keyword(s):  
Growth Hormone ◽  
Protein Kinase ◽  
C Protein ◽  
Releasing Hormone ◽  
Gh Secretagogues ◽  
Main Site ◽  
Gh Secretion ◽  
Kinase C ◽  
Growth Hormone Releasing Peptides

Growth hormone (GH)-releasing hormone and somatostatin modulate GH secretion. A third mechanism has been discovered in the last decade, involving the action of GH secretagogues. Ghrelin is a new acylated peptide produced mainly by the stomach, but also synthesized in the hypothalamus. This compound increases both GH release and food intake. The relative roles of hypothalamic and circulating ghrelin on GH secretion are still unknown. Endogenous ghrelin might amplify the basic pattern of GH secretion, optimizing somatotroph responsiveness to GH-releasing hormone. This peptide activates multiple interdependent intracellular pathways at the somatotroph, involving protein kinase C, protein kinase A and extracellular calcium systems. However, as ghrelin induces a greater release of GH in vivo, its main site of action is the hypothalamus. In this paper we review the available data on the discovery of ghrelin, the mechanisms of action and possible physiological roles of GH secretagogues and ghrelin on GH secretion, and, finally, the regulation of GH release in man after intravenous administration of these peptides.

Effect of cholinergic tone on growth hormone-releasing hormone-induced secretion of growth hormone in normal aging

1992 ◽  
Vol 4 (3) ◽  
pp. 231-237 ◽  
Author(s):  
Massimo Giusti ◽  
G. Marini ◽  
P. Sessarego ◽  
F. Peluffo ◽  
S. Valenti ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Normal Aging ◽  
Growth Hormone Releasing Hormone ◽  
Releasing Hormone ◽  
Cholinergic Tone

Growth Hormone-Releasing Hormone and Growth Hormone Secretagogues in Normal Aging

Endocrine ◽  
2003 ◽  
Vol 22 (1) ◽  
pp. 41-48 ◽  
Author(s):  
George R. Merriam ◽  
Robert S. Schwartz ◽  
Michael V. Vitiello
Keyword(s):  
Growth Hormone ◽  
Normal Aging ◽  
Growth Hormone Releasing Hormone ◽  
Growth Hormone Secretagogues ◽  
Releasing Hormone

Growth Hormone Releasing Hormone Treatment in Normal Aging

2001 ◽  
Vol 4 (4) ◽  
pp. 331-343 ◽  
Author(s):  
George R. Merriam ◽  
Suzanne Barsness ◽  
David Buchner ◽  
Monica Kletke ◽  
Lawrence H. Larsen ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Hormone Treatment ◽  
Normal Aging ◽  
Growth Hormone Releasing Hormone ◽  
Releasing Hormone

Effect of 15-day treatment with growth-hormone-releasing hormone alone or combined with different doses of arginine on the reduced somatotrope responsiveness to the neurohormone in normal aging

1995 ◽  
Vol 132 (1) ◽  
pp. 32-36 ◽  
Author(s):  
E Ghigo ◽  
GP Ceda ◽  
R Valcavi ◽  
S Goffi ◽  
M Zini ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Day Treatment ◽  
Normal Aging ◽  
Prolonged Treatment ◽  
Elderly Subjects ◽  
Growth Hormone Releasing Hormone ◽  
Releasing Hormone ◽  
Group A ◽  
Group B ◽  
Different Doses

Ghigo E, Ceda GP, Valcavi R, Goffi S, Zini M, Mucci M, Valenti G, Muller EE, Camanni F. Effect of 15-day treatment with growth hormone-releasing hormone alone or combined with different doses of arginine on the reduced somatotrope responsiveness to the neurohormone in normal aging. Eur J Endocrinol 1995;132:32–6. ISSN 0804–4643 It is well known that both spontaneous and growth hormone-releasing hormone (GHRH)-stimulated GH secretion undergo an age-related decrease; in addition, there is supportive evidence that the GH hyposecretory state of aging is of hypothalamic origin. The aims of the study in 35 normal elderly subjects (20 males and 15 females aged 65–89 years) were to verify whether the low somatotrope responsiveness to GHRH (1 μg/kg) can be primed by a daily GHRH treatment and whether the potentiating effect of both high intravenous (0.5 g/kg) and low oral (8 g) doses of arginine (ARG) on GH response to GHRH is maintained with time. In group A (N = 14) the GH response to GHRH on day 1 (AUC: 373.5 ± 78.5 μg·1−1·h−1) was unchanged after 7 (3720 ± 38 μg·1−1·h−1) and 15 days (377.9 ± 63.8 μg·1−1·h−1) of daily GHRH administration. In group B (N = 6) the GH response to GHRH co-administered with iv ARG on day 1 (1614.2 ± 146.2 μg · 1−1 · h−1) was higher (p < 0.05) than that of GHRH alone (group A) and persisted unchanged after 7 (1514.7±366.5 μg·1−1·h−1) and 15 days (1631.7 ± 379.1 μg · 1−1 · h−1) of treatment. In group C (N = 15) the GH response to GHRH co-administered with oral ARG on day 1 (950.6 ± 219.4 μg·1−1 · h−1) was higher (p < 0.03) than that of GHRH alone (group A) but lower (p < 0.05) than that to GHRH plus iv ARG (group B). It was unchanged after 7 (816.2 ± 208.5 μg·1−1 · h−1) and 15 days (760.4 ± 165.0 μg · 1−1· h−1) of treatment; these responses were still higher (p < 0.05) than that to GHRH alone. Insulin-like growth factor I levels were not modified by any of the treatments. In conclusion, our results demonstrate that in normal aging the low somatotrope responsiveness to GHRH is not improved by prolonged treatment with the neurohormone but it is enhanced by the combined treatment with ARG and this effect does not vanish after a 15-day treatment period. The effect of ARG is present even after a low oral dose, although less markedly than after a high intravenous dose. F Camanni, Divisione di Endocrinologia, Ospedale Molinette, C. so Dogliotti 14, 10126 Torino, Italy

scholarly journals Somatotroph recruitment by glucocorticoids involves induction of growth hormone gene expression and secretagogue responsiveness

2001 ◽  
Vol 169 (3) ◽  
pp. 499-509 ◽  
Author(s):  
TE Porter ◽  
CE Dean ◽  
MM Piper ◽  
KL Medvedev ◽  
S Ghavam ◽  
...  
Keyword(s):  
Gene Expression ◽  
Growth Hormone ◽  
Anterior Pituitary ◽  
Precursor Cells ◽  
Pituitary Cells ◽  
Caudal Lobe ◽  
Releasing Hormone ◽  
Gh Secretagogues ◽  
Gh Cells ◽  
Gh Gene

Prior research indicates that growth hormone (GH) cell differentiation can be induced prematurely by treatment with glucocorticoids in vitro and in vivo. However, the nature of these responses has not been fully characterized. In this study, the time course of corticosterone induction of GH-secreting cells in cultures of chicken embryonic pituitary cells, responsiveness of differentiated somatotrophs to GH secretagogues, localization of somatotroph precursor cells within the pituitary gland, and the effect of corticosterone on GH gene expression were determined to better define the involvement of glucocorticoids in somatotroph recruitment during development. Anterior pituitary cells from embryonic day 12 chicken embryos were cultured in 10(-9) M corticosterone for 4 to 48 h and were then subjected to reverse haemolytic plaque assays (RHPAs) for GH. Corticosterone treatment for as short as 16 h increased the percentage of GH cells compared with the control. When corticosterone was removed after 48 h and cells were cultured for an additional 3 days in medium alone, the percentage of GH secretors decreased but remained greater than the proportion of somatotrophs among cells that were never treated with corticosterone. To determine if prematurely differentiated somatotrophs were responsive to GH secretagogues, cells were exposed to corticosterone for 48 h and then subjected to GH RHPAs in the presence or absence of GH-releasing hormone (GHRH) or thyrotropin-releasing hormone (TRH). Approximately half of the somatotrophs induced to differentiate with corticosterone subsequently released more GH in response to GHRH and TRH than in their absence. The somatotroph precursor cells were localized within the anterior pituitary by culturing cells from the caudal lobe and cephalic lobe of the anterior pituitary separately. Corticosterone induction of GH cells was substantially greater in cultures derived from the caudal lobe of the anterior pituitary, where somatotroph differentiation normally occurs. GH gene expression was evaluated by ribonuclease protection assay and by in situ hybridization. Corticosterone increased GH mRNA in cultured cells by greater than fourfold. Moreover, corticosterone-induced somatotroph differentiation involved GH gene expression in cells not expressing GH mRNA previously, and the extent of somatotroph differentiation was augmented by treatment with GHRH in combination with corticosterone. We conclude that corticosterone increases the number of GH-secreting cells within 16 h, increases GH gene expression in cells formerly not expressing this gene, confers somatotroph sensitivity to GHRH and TRH, and induces GH production in a precursor population found primarily in the caudal lobe of the anterior pituitary, a site consistent with GH localization in adults. These findings support the hypothesis that glucocorticoids function to induce the final stages in the differentiation of fully functional somatotrophs from cells previously committed to this lineage.

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