In 35 young children, circadian rhythms of salivary cortisol levels were determined by ELISA using a commercially available kit with a minor modification. The concentration of labeled cortisol in the serum kit was reduced in order to measure cortisol in 10 μl of saliva. Intra- and interassay coefficients of variation for salivary cortisol ranged from 2.4 to 9.9 and 3.2 to 8.9%, respectively. Recovery of salivary cortisol was 82.9-107.0%. There was a highly significant correlation between cortisol levels in saliva and serum in adults (r = 0.857). Salivary cortisol levels ranged from 0.01 to 2.252 μg/l00 ml and showed significant diurnal variation in the children. Our ELISA is a precise, simple, noninvasive and useful method for clinical practice and study in infants and children.
ABSTRACT. The purpose of this study was to investigate the effect of constant light in a neonatal care unit on the development of the sleep-and-wakefulness rhythm in preterm infants. Two groups of infants (57 preterm infants without other complications and 58 healthy term infants) were prospectively studied over infancy by a day-by-day plot method, by which sleep-and-wakefulness states were recorded at home for more than 14 d to compare developmental courses of the sleep-and-wakefulness rhythm between the two groups at corrected and postnatal ages. In the two groups, there were no significant differences in distribution of emergence of periodicity of sleep states and wakeful states, total sleep time, nocturnal sleep time, diurnal sleep time, longest sustained sleep period, and longest sustained wakeful period at the same corrected ages. Moreover, the SD of the time of onset of the longest sustained sleep period of each subject diminished with increase in postconceptional weeks. The results suggest that the development of the sleep-and-wakefulness rhythm in preterm infants is not necessarily retarded if they are discharged from the neonatal care unit under constant light before an infant's innate biologic clock is mature enough to respond to an environmental cycle; rather it depends on their corrected ages. (Pediatr Res 33: 159-163, 1993)
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