Diurnal Cortisol Changes in Newborn Infants Suggesting Entrainment of Peripheral Circadian Clock<i>in Utero</i>and at Birth

Abstract

In the newborn infant, diurnal increase in cortisol was observed in the late afternoon and in correspondence with the birth time. The adrenal circadian rhythm acquired in utero may be reentrained by endocrinological events at birth. Such complex regulation of the adrenal circadian clock may inhibit a swift synchronization of the circadian clock to the day-night rhythm.