GROWTH
HORMONE (GH)
Properties
-
polypeptide (191
amino acids)
Sources
- anterior pituitary gland
Secretion and blood levels
- diurnal rhythm
- pulse in early night
- GHRH stimulates secretion
- exercise stimulates secretion
- GH stimulates IGF-I (somatomedin C) by liver
- IGF-I causes many GH effects
- IGF-I blood levels remain stable
- IGF-I inhibits GHRH secretion
- somatostatin inhibits GH secretion
- somatostatin from hypothalamus and gut
- GHRH / somatostatin negative feedback loop
- hexapeptides stimulate GH secretion
- some GH bound to proteins (GHBPs)
Physiological
Activities
- acts on many tissues
- muscle, bone, liver, kidney, heart, lymphoid tissues
- acts through cell membrane
- activates tyrosine phosphorylating enzyme
- increases AA uptake and protein synthesis
- increases blood glucose
Changes
with Aging
- height of nocturnal pulses decline
- 80 percent by age 80
- due to increased GHRH
- causes increased IGF-I levels
- liver retains sensitivity to GH
Effects
from GH Supplementation
- effects from chronic supplementation are unknown
- reported beneficial effects
- in GH deficient elders
- increases muscle mass, bone mass, skin thickness
- decreases body fat
- may increase immune function
- may increase healing
- reported adverse effects
- Na+ and H2O retention
- hypertension
- increases blood glucose
- decreases insulin sensitivity
- no increase in muscle strength
- gynecomastatia
- increases cognitive functions
- enlarged organs (kidney, spleen, liver)
- carpal tunnel syndrome
- osteoarthritis
- diabetes mellitus
- ? increases cancer growth ?
Effects
from Indirect GH Supplementation
- GHRH
- dose must be diurnal
- chronic GHRH losses effectiveness
- IGF-I
- does not reduce insulin sensitivity
- increases growth of certain cancers
- decreases normal apoptosis (programmed cell death).
- hexapeptides
- administered by nasal spray, orally, subcutaneous injection
- effects still unknown
- GH mimics
- effects include all GH effects (+ and -)
- net effects
- no conclusive evidence that GH slows aging
- does not affect all age changes
- may be harmful for individuals with normal GH
- indirect GH supplementation
- not shown to work well
- can lead to the same adverse as GH
- exercise provides increased GH levels and benefits
- without the drawbacks.
Caution
- questionable benefits
- questionable effectiveness over time
- serious drawbacks
© Copyright
2000 - Augustine
G. DiGiovanna - All rights reserved.
This material MAY be reproduced or distributed in any
form or by any means, or stored in any data
base or retrieval system ONLY under one of the following
two conditions: (1) If no individual, group,
organization, institution, company, corporation or other
entity is charged for its use and only for use by
instructors and students in courses where students are
required to purchase the book HUMAN
AGING: BIOLOGICAL PERSPECTIVES by Augustine G. DiGiovanna,
The McGraw-Hill
Companies, New York, 1994 or 2000; (2) If prior written
permission is obtained from Augustine G.
DiGiovanna, Ph.D., Salisbury University