The Hypothalamo-PituitaryAdrenal Axis
Table 10.1 Factors Influencing Evaluation of
Endocrine Function in Aging
Physiologic
Metabolism
Body Composition
Nutrition
Exercise
Stress
Hormone Metabolism
 Activity
T4  T3
T  DHT
Inter-endocrine Relations
Secretory Rate
Transport to target site
Number & Affinity
Of Receptors
Figure 10.1
Hypophysiotropic hormones
CRH: corticotropic releasing
hormone
GHRH: growth hormone releasing
hormone
GHIH: growth hormone inhibitory
hormone Somatostatin
PRH: prolactin releasing hormone
GnRH: gonadotropin releasing
hormone
TRH thyrotropin (TSH)-releasing
hormone
Pituitary Hormones
ACTH: adrenocorticotropin hormone
LH: lutenizing hormone
FSH: follicle stimulating hormone
PL: prolactin
TSH: thyroid stimulating hormone
GH: growth hormone
**Please see Figures 10.7-10.9 in text**
Figure 10.2
Figure 10.3 Diagram of a section of the adrenals illustrating the
various zones and hormones
Figure 10.6
Reminder
CRH: corticotropic
releasing hormone
ACTH:
adrenocorticotropic
hormone
Cortisol
Epinephrine
Norepinephrine
Actions Of Glucocorticoids
cellular
Actions of Adrenaline/Noradrenaline
Target
Figure 10.5 Schematic diagram of corticosteroid action in target cell
•Gene expression & new protein
synthesis
•Activation/repression of preexisting cell proteins
•Relatively long latency of onset
•Rapid onset of action
•Medium & long term cell
program
•Rapid adaptation to changes in
the milieu
•Organization of cell networks
for complex functions
•Dynamic modifications of long
term cell programs
Figure 10.7 Diagrammatic
representation of the anterior pituitary
Figure 10.8 Diagrammatic
representation of the posterior
pituitary
Changes with Aging in the
Hypothalamo-Pituitary-Adrenal Axis
No significant changes in healthy, non-stressed, elderly
The few changes that occur are rapidly compensated for
(e.g. decreased secretion of GCs from the adrenal cortex)
but also
less rapid metabolism in the liver & less urine excretion
Therefore the circulating levels remain constant
Also, normal ACTH & cortisol responses to CRH administration
Some alterations of the circadian rhythm
STRESS
Cortisol, norepinephrine, and epinephrine
Figure 10.4 Corticosterone titers in young (3-5 mo) and aged (24-28 mo) rats
Old rats
Young rats
Exposure to Stress Generates:
• Specific responses: vary with the stimulus
(specialized responses) and generate different
responses with each different stimulus.
• Nonspecific responses: (also called nonspecialized) are always the same
– regardless of the stimulus
– mediated through stimulation of neural,
endocrine, and immune axis