Adrenal Hormones and Adaptation to Stress
“Stress”, has become synonymous with the American
lifestyle. This phenomenon that has become such a
part of our daily vocabulary was identified over seventy
years ago by Hans Selye.(1) He described the occurrence
as nonspecific bodily changes that transpired in
response to physically harmful stimuli.(2) In his reporting,
Selye also indicated that although the adrenal glands
are the first glands to respond to stress, they are also
the first glands to fail under stressful conditions. The
body possesses a complex system for adapting to
stressful conditions. The ability of the organism to adjust
homeostasis and in turn increase the chance of survival
is dependent upon the activation of the stress system.
This activation in turn leads to both behavioral and
peripheral changes.(3)
The adrenal glands, a pair of triangular structures
located atop each kidney, play a key role in stress
adaptation and regulation. Not only are they necessary
for life, but they also play an essential role in energy
production and in controlling the conversion of
carbohydrate, protein and fat into blood glucose.
Moreover, they partake in the fluid and electrolyte
balance of cells, in the interstitial fluids, the blood
stream, as well as in fat storage. They are also an
important component in the production of sex
hormones, especially following menopause.
The adrenal cortex secretes four major groups of
hormones, classified as the glucocorticoids, the
mineralcorticoids, androgens and estrogens. The
adrenal medulla is responsible for the secretion of
the catecholamines, particularly epinephrine and
norepinephrine. The secretion of all adrenal steroids,
including the glucocorticord, cortisol, is under the
control of pituitary adrenocorticotropic hormone
(ACTH), which functions by a negative feedback
mechanism. Consequently, a high level of circulating
cortisol will suppress the secretion of ACTH, while a
drop in cortisol will result in an increased ACTH
secretion.(4) The action of the glucocorticoids is catabolic,
stimulating the breakdown of protein and the inhibition
of protein synthesis. Increased cortisol initiates fat
deposition in adipose tissue, and consequently, weight
gain is common with cortisol excess. Blood glucose
homeostasis is also affected by cortisol, and its action is
two-fold: via the stimulation of hepatic gluconeogenesis
and via the inhibition of glucose uptake by tissues.
Additionally, both the inflammatory and immune
responses are suppressed by glucocorticoids, and thymic
and lymph atrophy are known to develop in the presence
of excess cortisol.(4)
Cortisol, the prototype of the glucocorticoids, is the
hormone synthesized in the greatest quantity by the
adrenal glands; approximately two hundredfold that
of aldosterone. It exerts numerous physiologic actions
on the body, including maintenance of normal blood
pressure, regulation of fluid and electrolyte balance,
protein metabolism, body fat distribution, glucose
metabolism, and normal muscle formation. It also exerts
action on both the hematopoietic system (blood cell
formation) and on the lymphatic tissues.(4) Secretion
takes place in a diurnal pattern - with the highest value
between 6 and 8 a.m.and the lowest around midnight.
Dysregulation of the stress system or a maladaptive
neuroendocrine response has the potential to result
in disturbances in growth and development, and
may ultimately result in other health consequences
including psychiatric, endocrine/metabolic, and/or
autoimmune imbalances, as well as vulnerability to
