The Development of Circadian Rhythms in Human Infants

6 Results
DESCRIPTION OF THE URINARY EXCRETION OF CORTISOL
6.1 Analysis of urinary cortisol
Night time and morning cortisol samples (from urine) were obtained from all infants
in the study. This chapter presents the results of the analysis of these. As was the
case for melatonin, only two sampling times for every 24 hour period were measured.
This was to try to maintain simplicity of the monitoring schedule as several
physiological parameters as well as the measurement of gene expression in the infant
were being undertaken concurrently. All results are expressed as mg/ml creatinine to
correct for renal excretion.
Samples were collected at or as close to midnight (night time samples) and midday
(day time samples) on the subsequent day over a 24 to 48 hour period at weekly
intervals. The infants ranged from 5 to 17 weeks of age during the period of data
collection. The change of night time and day time secretion of cortisol with postnatal
age was examined. Cosinor analysis was not applied to cortisol data.
A total of 466 urine samples were collected from 34 infants recruited into the study.
Twenty samples were insufficient for cortisol analysis. Three methods for urine
collection were used: U-bag collection system, clean catch and urine pads in the
nappies. All samples were assayed in duplicate and a mean value used.
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