The Development of Circadian Rhythms in Human Infants

1.7 Cortisol
Cortisol is a hormone, secreted by the adrenal glands, which has been shown to
exhibit one of the most robust circadian rhythms. It is produced in antiphase to
melatonin. The role it plays in the „clock‟ and circadian rhythmicity is an emerging
and exciting area of research. It has traditionally been a „cross over‟ measure quoted
frequently in psychosocial and biological work as a physical measure of „stress.‟ In
molecular biology work is has been found to synchronise the clock (see introduction
section 1.9.6). It was included as a measure of interest in this study as it may be the
„key‟ that unlocks the door to physiological maturation. We do not know the precise
role it plays in chronobiology and the consequence of early or late maturation of the
corticosteroid axis/rhythm; therefore it is worth exploring.
1.7.1 Production and Regulation of Cortisol Secretion
Cortisol is a hormone which is essential for life. It accounts for 95% of
glucocorticoid activity. It has a major role in the body‟s ability to process and
metabolise glucose, protein and fats. It also facilitates the body‟s normal response to
stress. In its absence, a minor illness can cause death.
Cortisol is made from cholesterol. It is produced in the adrenal cortex. Cholesterol is
acted upon by the enzyme cholesterol desmolase and as a result pregnenolone is
made. This is then converted to 17-hydroxypregnenolone; then to 17-
hydroxyprogesterone; onto 17-deoxycortisol and finally to cortisol.
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