Blood period (1-4). This circadian rhythm in hormone secretion

Blood levels of many
hormones oscillates during 24 hour period (1-4). This circadian rhythm in hormone secretion is not only affected by
Sleep / wake cycle (such as GH) but also an endogenous biological timing system
(such as cortisol). Appropriate interaction of sleep and biological system is
necessary for regulating  blood hormone
concentration. Under normal situations the sleep/ wake cycle and
endogenous timing system are coordinated and properly regulate levels of
hormones. However, circadian misalignment may have negative adverse health
consequences on metabolic and hormonal factors (5).

Ghrelin, a 28-amino-acid peptide was
purified in 1999 from rat stomach. Ghrelin
is produced by the oxyntic gland in the stomach (6). Peripheral or central injection of ghrelin increases intake
of food and body weight in rodents(7,8). Plasma  human ghrelin levels increase prior the usual meal
times and fall thereafter (9,10).

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Therefore, it seems ghrelin secretion regulate by caloric intake.  Ghrelin also  plays a role in neuroendocrine and behavioral responses to stress (11).

Previous reports have shown
the release of hormones such as ghrelin and leptin, which play a central role
in regulating glucose and appetite is dependent on sleep duration and quality.
Therefore, sleep loss may have adverse effects on endocrine function and metabolism
(12).

Few studies have been conducted on the 24-hour pattern of ghrelin
secretion in people who have a normal sleep duration (13,14). but with our knowledge, no studies has been done
on the effects of sleep deprivation on this pattern.Therefore, our study
was done to establish whether :

 1) Does the serum ghrelin levels follow a
circadian rhythm in soliders with normal sleep.

 2) Does the shift work affect the pattern of
24 hours of ghrelin secretion?

Material
and methods

Participants

The
study was conducted on healthy young soldiers who served in AJA university of Medical
sciences. They had 19-23 years old. After the
necessary explanations in relation to this research they were invited to
participate in this study. 16 soldiers accepted our
invitation. First group had regular sleep-wake cycle. The soldiers were
sleeping from 22 pm until 6 am and woke the rest of the day and were doing
their daily tasks. The second group consisted of individuals who had not normal
arousal cycle. Their plan within 24 hours was: Two hours
awake for guard, standby two hours and sleep two hours. The program was repeated during 24 hours.

Participants in the
study were given meals three per day (breakfast, lunch, dinner) at specified
times.

Blood sampling and hormone assay

Blood samples were taken at four hour intervals during both wakefulness
and sleep for a total of 24 hours (from 10
A.M on day 1 until 6 A.M on day 2). Therefore, six blood samples were taken
from each subject within 24 hours.

Blood
was collected in tubes, which were stored on ice and contained Na-EDTA (1 mg/ml
blood) 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 frozen
to ?20°C until the various assays were performed

Serum cortisol
(DRG Instruments GmbH, Germany) and ghrelin (CRYSTAL DAY CHRISTIAN DAY kit – China) Concentrations
were measured by ELISA method.

The calculations

The average hormone concentrations were
calculated as the area under the curve divided by 24 h 15.

Statistical analysis

All values are expressed as means ± SEM. A normal distribution of
data was evaluated by sample Kolmogorov- Sminov test. To determine the existence of the daily changes in the secretion of the
hormones, we used repeated measures
analysis of variance (ANOVA) with time as within
subject factor and condition (normal sleep vs. sleep deprived) as between
subject factor.

The Independent t-test was used to compare the average
concentration of hormones over 24 hours in the two groups. SPSS software (version
18.0, IBM) was used for all statistical analyses. The
p- value less than 0.05 were considered significant

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