Earlier studies have been shown an alteration in activity times, changeshappen in sleep period and feeding behavior together influence circadiancontrol of the endocrine system (16,17).
In our study, secretion pattern of cortisol is similar tothe 24 hours rythm of cortisol seen in previous reports (3,12) with peaklevels occurring at early morning (06.00 p.m.) and sleep deprivation had no significant effect on thispattern. The results of Scheer et.al (2009) study showed, the cortisol secretion pattern is more influenced by the internaldaily rhythms rather than behavior (fasting-feeding and sleep/wake) cycles (18).The study Fumihisa et al.
(2013) showed that nightshift (from 0:00 to 8:00) had not effect on circadian rhythm in male nurses. Inaddition, the concentration ofcortisol in night shift did not differfrom that of the control group (19). Also in our study, the average concentrationof cortisol throughout 24 h was notsignificantly higher in the deprived sleep group than the control group.In agreement with presentstudy, an earlier study, did not show a significant circadianrhythm for acylated ghrelin in the normalsubjects that take 3 meals in a day (14). It seemsthat the nutritional state of the person is effective on ghrelin secretionpulses. Fasting augmented all parameters of ghrelin pulsatile secretion (20).
In contrast to our study, some previous studies havereported circadian rhythm for ghrelin (13). This can be due tomethodological differences that prevented comparison this study with other works.1- The number of blood sampling: In ourstudy, The number of blood sampling was 6 times during 24 hours. Whereas in otherworks were between 24-72 during 24 hours(14,13,21). 2- Age and sex. Most preceding studiesthat reported circadian rhythm for ghrelin have been done in female subjects anda very large age range (13,21).
3-sleep and sleepdeprivation condition. In most previous studies, effects of sleep on a diurnalor nocturnal pattern of ghrelin secretion investigated in the laboratoryconditions not imitating “real life.In conclusion, It seems, ghrelin does not show a circadian rhythm andsleep deprivation has no significant effecton the 24 h secretion pattern of cortisol and ghrelin.Limitations:The small number of subjects and lownumber sampling over 24 h are limitations.