Earlier rather than behavior (fasting-feeding and sleep/wake)

Earlier studies have been shown an alteration in activity times, changes
happen in sleep period and feeding behavior together influence circadian
control of the endocrine system (16,17).

In our study, secretion pattern cortisol is similar to the 24
hours rythm of cortisol seen in previous reports (3,12) with peak levels
occurring at early morning (06.00 p.m.) and sleep deprivation had no
significant effect on this pattern. The results of Scheer et.al (2009) study showed, the cortisol secretion pattern is more influenced by the internal
daily rhythms rather than behavior (fasting-feeding and sleep/wake) cycles (18).

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The study Fumihisa et al. (2013) showed that night
shift (from 0:00 to 8:00) had not effect on circadian rhythm in male nurses. In
addition,  the concentration of
cortisol  in night shift did not differ
from that of the control group (19). 
Also in our study, the average concentration
of cortisol throughout 24 h  was not
significantly higher in the deprived sleep group than the control group.

In agreement with present
study, an earlier study, did not show a significant circadian
rhythm for acylated ghrelin in  the normal
subjects that take 3 meals in a day (14). It seems
that the nutritional state of the person is effective on ghrelin secretion
pulses. Fasting augmented all parameters of ghrelin pulsatile secretion (20). In contrast to our study, some previous studies have
reported circadian rhythm for ghrelin (13). This can be due to
methodological differences that prevented comparison  this study with other works.

1- The number of blood sampling: In our
study, The number of blood sampling was 6 times during 24 hours. Whereas in other
works were between 24-72  during 24 hours

2- Age and sex. Most preceding studies
that reported circadian rhythm for ghrelin have been done in female subjects and
a very large age range (13,21).

3-sleep and sleep
deprivation condition. In most previous studies, effects of sleep on a diurnal
or nocturnal pattern of ghrelin secretion investigated in the laboratory
conditions not imitating “real life.

In conclusion, It seems, ghrelin does not show a circadian rhythm and
sleep deprivation has no significant effect
on the 24 h secretion pattern of cortisol and ghrelin.


The small number of subjects and low
number sampling over 24 h are limitations.