Blood levels of manyhormones fluctuates during 24 hour period (1-4). This circadian rhythm in hormone secretion is not only affected bySleep / wake cycle (such as GH) but also an endogenous biological timing system(such as cortisol). Appropriate interaction of sleep and biological system isnecessary for regulating hormone levels. Under normal situations the sleep/wake cycle and endogenous timing system are coordinated and properly regulatelevels of hormones. However, circadian misalignment may have negative adversehealth consequences on metabolic and hormonal factors (5).Ghrelin, a 28-amino-acid peptide waspurified in 1999 from rat stomach. Ghrelinis produced by the oxyntic gland in the stomach (6).
Peripheral or central administration of ghrelin increases foodintake and body weight (7,8). In rodents. Plasma human ghrelin levels rise prior to habitual mealtimes and fall thereafter (9,10).
Therefore, it seems ghrelin secretion regulate by caloric intake. Ghrelin also plays a role in neuroendocrine and behavioral responses to stress (11).Previous reports havebeen shown the release of hormones such as ghrelin and leptin, which play acentral role in regulating glucose and appetite is dependent on sleep durationand quality. Therefore, sleep loss may have adverse effects on endocrinefunction and metabolism (12). Afew research has been done in relation to 24-h ghrelin secretion pattern innormal subjects (13,14) but with our knowledge, no studies has been done on theeffects of sleep deprivation on this pattern.Therefore, the present study wasdone to establish whether : 1) Serum ghrelin levels follow a circadianrhythm in normal sleep soliders 2) Determine effect shift work on 24 hour ghrelin pattern.Materialand methodsParticipantsThestudy was conducted on healthy young soldiers who served in AJA university of Medicalsciences. They had 19-23 years old.
After thenecessary explanations in relation to this research they were invited toparticipate in this study. 16 soldiers accepted ourinvitation. First group had regular sleep-wake cycle. The soldiers weresleeping from 22 pm until 6 am and woke the rest of the day and were doingtheir daily tasks. The second group consisted of individuals who had not normalarousal cycle.
Their plan within 24 hours was: Two hoursawake for guard, standby two hours and sleep two hours. The program was repeated during 24 hours.Participants in thestudy were given meals three per day (breakfast, lunch, dinner) at specifiedtimes.Blood sampling and hormone assayBlood samples were taken at four hour intervals during both wakefulnessand sleep for a total of 24 hours (from 10A.M on day 1 until 6 A.M on day 2). Therefore, six blood samples were takenfrom each subject within 24 hours.
Bloodwas collected in tubes, which were stored on ice and contained Na-EDTA (1 mg/mlblood) and aprotinin (300 kallikrein inhibitor units/ml blood). Immediately after the withdrawal, blood was centrifuged at 2,600 g for 7 min at 4°C, and serum was aliquoted and frozento ?20°C until the various assays were performedSerum cortisol(DRG Instruments GmbH, Germany) and ghrelin (CRYSTAL DAY CHRISTIAN DAY kit – China) Concentrationswere measured by ELISA method.The calculationsThe average hormone concentrations werecalculated as the area under the curve divided by 24 h 15.
Statistical analysisAll values are expressed as means ± SEM. A normal distribution ofdata was evaluated by sample Kolmogorov- Sminov test. To determine the existence of the daily changes in the secretion of thehormones, we used repeated measuresanalysis of variance (ANOVA) with time as withinsubject factor and condition (normal sleep vs. sleep deprived) as betweensubject factor.
The Independent t-test was used to compare the averageconcentration of hormones over 24 hours in the two groups. SPSS software (version18.0, IBM) was used for all statistical analyses. Thep- value less than 0.05 were considered significant
