Stress response: Endocrine and metabolic changes

Question 1

Stress response: Endocrine and metabolic changes?

Answer 1

• Surgery precipitates hormonal and metabolic changes causing the stress response.
• Stress response is associated with: substrate mobilization, muscle protein loss, sodium and water retention, suppression of anabolic hormone secretion, activation of the sympathetic nervous system, immunological and haematological changes.
• The hypothalamic-pituitary axis and the sympathetic nervous systems are activated and there is a failure of the normal feedback mechanisms of control of hormone secretion.

Question 2

A summary of the hormonal changes associated with the stress response?

Answer 2

Increased Decreased No Change

GH Insulin TSH

Cortisol Testosterone LH

Renin Oestrogen FSH

(ACTH)

Aldosterone

Prolactin

Antidiuretic hormone

Glucagon

Question 3

During stress what does the Sympathetic nervous system do?

Answer 3

• Stimulates catecholamine release
• Causes tachycardia and hypertension

Question 4

During stress what does the pituitary do?

Answer 4

• ACTH and growth hormone (GH) is stimulated by hypothalamic releasing factors, corticotrophin releasing factor (CRF) and somatotrophin (or growth hormone releasing factor)
• Perioperative increased prolactin secretion occurs by release of inhibitory control
• Secretion of thyroid stimulating hormone (TSH), luteinizing hormone (LH) and follicle stimulating hormone (FSH) does not change significantly
• ACTH stimulates cortisol production within a few minutes of the start of surgery. More ACTH is produced than needed to produce a maximum adrenocortical response.

Question 5

What happens to cortisol during stress?

Answer 5

• Significant increases within 4-6 hours of surgery (>1000 nmol litre-1).
• The usual negative feedback mechanism fails and concentrations of ACTH and cortisol remain persistently increased.
• The magnitude and duration of the increase correlate with the severity of stress and the response is not abolished by the administration of corticosteroids.
• The metabolic effects of cortisol are enhanced:

Question 6

What happens to growth hormone during stress?

Answer 6

• Increased secretion after surgery has a minor role
• Most important for preventing muscle protein breakdown and promote tissue repair by insulin growth factors

Question 7

What happens to Antidiuretic hormone during stress?

Answer 7

An important vasopressor and enhances haemostasis

Renin is released causing the conversion of angiotensinogen to angiotensin I

Angiotensin II formed by ACE on angiotensin 1, which causes the secretion of aldosterone from the adrenal cortex. This increases sodium reabsorption at the distal convoluted tubule

Question 8

What happens to insulin during stress?

Answer 8

• Release inhibited by stress
• Occurs via the inhibition of the beta cells in the pancreas by the α2-adrenergic inhibitory effects of catecholamines
• Insulin resistance by target cells occurs later
• The perioperative period is characterized by a state of functional insulin deficiency

Question 9

What happens to Thyroxine (T4) and tri-iodothyronine (T3) during stress?

Answer 9

• Circulating concentrations are inversely correlated with sympathetic activity.
• After surgery there is a reduction in thyroid hormone production, which normalises over a few days.