Cortisol
End hormone or mediator · Zona fasciculata CBG bound Diurnal
The end hormone of the corticotrophic axis, about 90% carried on cortisol-binding globulin with a half-life of 60-90 minutes. It is catabolic, permissive for catecholamines and immunosuppressive.
Traced from the start
Detail
- Actions
- Gluconeogenesis and insulin resistance, protein catabolism, lipolysis with central fat redistribution, permissive vascular response to catecholamines, suppression of inflammation and of osteoblasts
- Mineralocorticoid effect
- Cortisol binds the mineralocorticoid receptor with equal affinity; 11-beta-hydroxysteroid dehydrogenase type 2 inactivates it in the kidney, and liquorice or very high cortisol overwhelm this to give hypokalaemic hypertension
- Binding globulin
- Oestrogen in pregnancy or the combined pill raises CBG and therefore total cortisol with no change in free cortisol
- Testing
- A 9 am cortisol under about 100 nmol/L supports insufficiency; a short synacthen peak above roughly 500 nmol/L (assay-dependent) excludes it
When it goes wrong
Chronic glucocorticoid excess from any cause
Central obesity, proximal myopathy, thin skin with purple striae and easy bruising, hypertension, diabetes, osteoporosis and mood disturbance
Adrenal crisis from intercurrent illness, missed doses or abrupt steroid withdrawal
Fluid-resistant hypotension, hypoglycaemia, hyponatraemia and abdominal pain; give 100 mg hydrocortisone IV and fluids before any result returns
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